Datum 4040A Problems - Page 1
Forum section: electronics / general

author: EMUD
author_rank: Regular Contributor
timestamp: July 13, 2018, 06:56:56 pm
content: Hello,now I am an owner of a Datum 4040A cesium frequency standard. But, the unit did not work, after starting it, it locked, but 2 hours later it unlocked and reported error 2 and 3. (I am using the terminal software monitor3.exe on a Win 7 computer).After unlocking the unit did lock again after some minutes, then it unlockes again and so on. After switching it off an let it cool down the cycle above can be repeated.Are there any ideas how to start the diagnosis?Best regards and many thanksEMUD

author: edpalmer42
author_rank: Super Contributor
timestamp: July 14, 2018, 04:02:11 am
content: Quote from: EMUD on July 13, 2018, 06:56:56 pmThere's almost no info available on the 4040A. However, the 4040B lists errors 02 and 03 as:02 Rabi-Ramsey error >40 mV03 Rabi-Zeeman error >160 mVBy themselves, those don't tell me anything so .........1. Start reading:https://www.eevblog.com/forum/metrology/no-luck-on-my-first-attempt-at-acquiring-a-cesium-frequency-standard/?all2. Post a copy of the Monitor3 Main Status Window showing the data while it's locked and a second copy showing the data when the lock fails.Don't start tearing the thing apart yet. Let's look over the Main Status Window data first.What resources do you have available? Can you confirm that the output frequency is at 10 MHz exactly or is it 'stuck' on one side or the other of 10 MHz. Do you have a GPSDO or a calibrated Rubidium standard?Ed

author: texaspyro
author_rank: Super Contributor
timestamp: July 14, 2018, 05:19:59 am
content: How is the ion pump current? If it's been in storage for a while it can take weeks for it to pump down. Worst case you may need an external high voltage supply for it to pump down... if it's even possible.Also what about the beam current? It could be out of cesium. A new tube ($30K ?) may be needed.

author: EMUD
author_rank: Regular Contributor
timestamp: July 14, 2018, 08:25:00 am
content: Hello,ok, thanks for help.I have the following instruments :- rubidium 10MHz systems (calibrated against a GPSDO)- GPSDO 10 MHz and 1PPS- 100MHz scope, 2 ch- spetrum analyzer 8GHz- rf generator up to 5.6 GHz- hi res counter with ocxoI have read the mentioned threat and the manual of the 4040B and the CSIII.(I have tried to understand the theorie of operation in the CSIII manual,but I have to read it several times to understand it)The 4040A here seemed to be one of the last 4040A units, it was made 1998.I have attached the pdfs from the working unit and the error condition.About the ion pump : the unit was stored with pump active, the current is about 1uA.Has anyone tried to check the tube by applying a rf generator instead of the 12,8MHzmodulation signal and test the response of it ? Could that be a way to check the health(not how much CS is left...) of these tubes ... The tube seemed to be somekind of aresonator, so it could be possible to check it in this way. Yes the generator has to be agood resolution.ThanksEMUD

author: edpalmer42
author_rank: Super Contributor
timestamp: July 14, 2018, 04:40:49 pm
content: Your unit looks basically healthy. Even when it loses lock, the Clock Signal (Cesium beam level) is basically constant and the level is good. Even the Zeeman Signal stays good. The only thing I'm questioning is the OCXO CV. It should be between about 0.5V and 5.0V. It's been a while since I looked at mine. Is there a coarse tuning adjustment on your oscillator? If so, try tweaking that to see if you can get that voltage to rise. OCXOs drift, so it wouldn't surprise me if it needed a tweak to bring it back where it should be. If there isn't a coarse tuning adjustment, I'd recommend removing the oscillator from the unit and powering it on the bench. Leave it powered for a week, or a month, and see if it drifts back. Don't try this while the oscillator is in the 4040A. There's no way to have the oscillator powered without using up your precious supply of Cesium! Actually, it would be useful to power the OCXO on the bench and run the EFC from one end to the other to see what the frequency range is. However, if the OCXO needs a lot of time to drift back where you want it, you'll probably have to do something so that it's at a reasonable frequency after a short warmup so that you don't waste Cesium.Two other things you should check are the power supply capacitors under the metal lid and the outputs of the STEL-1173. You might consider adding a small heat sink to the 1173. I don't know if it will help, but that chip is prone to failure and does run hot. It can't hurt. You should also check the outputs of the 1173 to see if it's started to fail. You mentioned that yours seems to be a more recent unit so that might not be a problem for you - yet!Regarding the tube testing, yes it's possible. I discussed it in the other thread and posted the results for my tube. You need a synthesized generator in the 12.8 MHz area that's referenced to your Rb standard, a DMM that has an input impedance of 100M or more, and a computer that can control the generator and read the value from the DMM. If you're a real glutton for punishment you could take the readings manually. Disconnect the tube's output and connect the DMM to the tube. Configure things so that the tube sees a 100M ohm load. Connect the generator in place of the 12.8 MHz source. Sweep the generator from maybe 12.5 to 13.0 MHz and measure the result. You should see something like the graph below. I stepped the generator in 10 Hz steps. Now, I wish I'd used 1 Hz steps.This isn't a perfect test because while you're doing this, the processor is going crazy trying to change a bunch of parameters to try and find the signal that you disconnected. But, my results seemed reasonable. The level was significantly lower than you'd get from an HP 5061A Cesium, but the 5061A manual includes a calculation (paragraph 5-164) to check the beam signal quality. According to that, my tube is great - if that calculation even makes sense on a different unit.Ed

author: EMUD
author_rank: Regular Contributor
timestamp: July 15, 2018, 09:22:11 am
content: Hello Ed,thanks for your opinion about my unit. Yes, it makes sense to test the oscillator at first. I will use the following test setup on my bench:24V Power supply for the oscillator and the oven0 - 5V Simulator for the frequency controlTAIT Rubidium for the reference of my frequency counterFrequency counter TR5212 Takeda (resolution 0.1Hz)The oscillator is a DATUM 1111, a picture is added. It has a hole in its housing, so it may be recalibrated. I will check this.If there are results I will post them this evening.I have discovered, that the values displayed in monitor3 did not match the values in the real unit, the attenuator i. e. seemed to be a current controlled PIN diode type, its voltage is 0,7 to 0,4V. Do you have any idea about that?The other thing is to check the 12,8MHz from the frequency generation (STEL ... ) with a spectrum analyzer. I think that this cound make sense to see the points where the tube is measured. (the osc frequency control should be blocked for this)Thanks and best regardEMUD

author: EMUD
author_rank: Regular Contributor
timestamp: July 15, 2018, 01:44:03 pm
content: Hello,here are the results of my oscillator :EFC Frequency+5V 9999989.9Hz+4V 9999991.9Hz+3V 9999993.9Hz+2V 9999995.9Hz+1V 9999997.8Hz0V 9999999.8Hz-1V 10000001.6Hz-2V 10000003.7Hz-3V 10000005.6Hz-4V 10000007.6Hz-5V 10000009.5HzI have checked the frequency at 0V for 4 hours, there was no drift (only the last digit jumps between 7 and 8 )I think a recalibration is not needed.Thanks for helpEMUD

author: edpalmer42
author_rank: Super Contributor
timestamp: July 15, 2018, 05:00:31 pm
content: Your OCXO does seem to be centered around 0 volts doesn't it? The funny thing is, I only know of a handful of units and all of them have tuning voltages that are positive. e.g. +1V3, +3V3, +2V8, +3V0. It isn't clear to me that negative voltages are allowed. Yes, I have seen documentation that says they are, but I've seen ranges of either +- 0V5 or +- 4V5 so I'm suspicious. I'd still recommend that you tweak the frequency to move the EFC voltage higher. Your symptom of lock then no lock with constant Cesium levels could easily be due to the OCXO tuning being at the end of it's range. It's an easy test to do and can be just as easily reversed if necessary.By the way, when the lock fails, what happens to the output frequency?QuoteSorry, I don't understand the question. Are you talking about the EFC voltage that controls the varactor diode in the oscillator to adjust the frequency? If Monitor3 isn't reporting the actual EFC voltage then there's a hardware problem, but it might not affect the unit's operation.QuoteIt could be tricky to look at that output on a spectrum analyzer, or a scope for that matter. If you look at the circuit description, the processor bounces that frequency up and down many times a second to look at various characteristics of the signal to test the accuracy and health of the unit. One time I tried to count all the frequencies. I think I came up with something like 15 discrete values that are all tested each second (?). I don't know of a way to stop that. Based on these tests, the OCXO is nudged via a D/A converter to the correct frequency. It isn't just a PLL.You can go ahead and look at the 12.8 MHz signal. Depending on the resolution of your spectrum analyzer, all the test frequencies could be so close together that they just look like one frequency. Remember that since the frequencies are generated by a Numerically Controlled Oscillator and then filtered, they'll probably be rather dirty. That won't have any effect on the unit's operation as long as the fundamental frequency is correct.Ed

author: EMUD
author_rank: Regular Contributor
timestamp: July 15, 2018, 06:28:03 pm
content: Hi Ed,the EFC seemed to be the same than the value in monitor3. But the attenuator setting is just not the actual voltage at the attenuator (the unit between the multiplier and the tube ) ...The osc control voltage seemed ok to me. EFC is just the same range as the often mentioned HP10811. In this unit the varicaps cathode is connected to a reference voltage of +6.4V . So the range is from +5 to -5V specified (anode varycap).OK, I will come back when the osc is corrected and the caps in the pwr supply are checked.Best regardsEMUD

author: edpalmer42
author_rank: Super Contributor
timestamp: July 15, 2018, 07:24:32 pm
content: I think your comparison to the HP10811 is quite correct. Out of curiosity I pulled apart my Datum 1111B oscillator and thought I was looking at a Hewlett Packard 10811. The aluminum block enclosing the crystal looks identical. I didn't do a detailed reverse engineering on it, but I wondered if HP ever OEM'd the 10811 to other manufacturers.My thought on the EFC voltage wasn't whether it would be accepted by the oscillator, but could the 4040A can actually produce a negative voltage.I've never looked closely at the attenuator you mentioned so I can't help you there.Ed

author: EMUD
author_rank: Regular Contributor
timestamp: July 17, 2018, 05:07:29 am
content: Hi Ed,yesterday I have disassembled the oscillator to look how to tweak it. There was a hole on the back, but no screw to adjust. I have added a picture of the oscillator pcb, but there is no variable cap and no pot to adjust. Only a pot to adjust the output voltage (the osc has a automatic level control !). The Datum people have replaced the variable cap with a normal cap ... so there is no possibility to tweak. I will examine the the path of the control voltage (I think from the BB 16bBit DAC) to the EFC in the next days.I think the 1111B is a very similar to the HP osc, the pcbs have only minor differences.best regardsEMUD

author: edpalmer42
author_rank: Super Contributor
timestamp: July 17, 2018, 06:27:43 am
content: Who was the idiot who said this would be an easy test??Okay, put everything back together. Now, disconnect the output of the 1111B from the rest of the 4040A and use it as the external reference for your synthesized generator. Connect the output of the generator to the point where you'd normally connect the output of the 1111B. What you're doing is using the synthesized generator to tweak the frequency seen by the 4040A. The 4040A will still control the frequency of the 1111B and the 1111B output will nudge the output of the generator. The reference frequency for the generator has some wiggle room around 10 MHz. Each type of generator has a different window that it will accept. Often, that window isn't spec'ed. My Stanford Research DS345 generator is spec'ed as +-2ppm (i.e. +-20Hz).You've already determined that the 1111B shifts by 10 Hz for a 5V change in EFC. (Note: there appears to be a typo in the data you listed earlier: +5V is only 1.1 Hz low - I'd expect to see more like 10.1 Hz). Also, a higher EFC voltage results in a lower frequency. So if you set the generator output for 10MHz + 5Hz, the 4040A will try to reduce the frequency by raising the EFC voltage. Similarly, if you set the generator for 10 MHz - 5Hz, the 4040A will have to send a negative EFC voltage to drive the frequency higher. This will prove whether or not the 4040A can generate negative EFC voltages or whether the -163mV shown on the Monitor3 screen is a problem.Do you understand all that? I'm not sure I do!If I got that all right, setting the generator output for 10 MHz + 5 Hz should drive the EFC to something like +2V5. Depending on how clean the output of your generator is, you might or might not get a good lock.Ed

author: EMUD
author_rank: Regular Contributor
timestamp: July 18, 2018, 04:19:36 am
content: Hi Ed,first I thought, what a strange idea to shift the frequency with a signal generator ... but, it works ! I have added the results the 4040a is able to generate a positive and negative EFT ! I have added the results.I think it is fact that the osc is not guilty ! I will check the pwr supply next.Best regardsEMUD

author: edpalmer42
author_rank: Super Contributor
timestamp: July 18, 2018, 05:51:43 am
content: Yes, that trick to shift the frequency is quite bizarre, isn't it? I've used it once or twice for testing a system where the OCXO has drifted beyond its adjustment range. I've also used it when I wanted an odd frequency that was tunable with an EFC voltage. Just use a 10 MHz OCXO that has EFC as the external reference for the generator that generates the odd frequency.The thing I find so bizarre about your OCXO is that it isn't adjustable, it's 20 years old, and the tuning range is almost exactly centered around 10 MHz. Who needs Cesium, you've got a quartz oscillator that hasn't aged in 20 years!But the measurements seem conclusive so yes, it's time to move on. It's actually too bad that this wasn't the problem since the fix would be easy.If you remove the metal plate that's inside the unit - the one that has the 5045A label on it - you'll see the capacitors that were bad in Hydrogen Maser's 4040A. You can compare your voltage readings to the ones I posted in the other thread. Also check for bad solder joints on the DC-DC converters.When your unit loses lock, do you have it laying flat or is it in some other orientation? I had mine standing on its side. Everything was fine and then all hell broke loose! Luckily, I was logging data at the time so I was able to capture the carnage. The attached graph shows multiple incidents mashed together so the horizontal scale isn't significant. The vertical axis shows the actual values of the four parameters. Bottom line is - always keep the unit horizontal when it's operating!Don't forget to check the outputs of the STEL-1173. You don't have to try and analyze what they're doing, just make sure that they're toggling between 0 and 5V. Apparently, when the chip starts to fail, the outputs randomly start failing one at a time. Depending on which ones fail and whether they just stop or intermittently stop and start, you could see symptoms similar to yours.Ed

author: bostonman
author_rank: Super Contributor
timestamp: March 18, 2019, 07:27:10 pm
content: 02 Rabi-Ramsey error >40 mV03 Rabi-Zeeman error >160 mVI didn't read the entire thread, but these errors indicate a poor cesium beam tube or a noisy oscillatore. What is the 9GHz microwave level? It should be around 2500 if I remember correctly.

author: testpoint1
author_rank: Frequent Contributor
timestamp: February 16, 2020, 04:10:23 pm
content: Quote from: EMUD on July 13, 2018, 06:56:56 pmplease check the 10MHz output, if that is near 10.000000MHz , just several milli Hz offset, not stable, that means your OCXO is OK, nothing about it.

author: notfaded1
author_rank: Frequent Contributor
timestamp: February 16, 2020, 05:34:25 pm
content: Rudi-Boy you're lucky your 4040A really has the serial output on it! That's wonderful news and that you're getting some lock. I have a feeling you're in better shape than I am right now and I'm glad you started a thread too. Any new info is good for me and my mine.Bill

author: bostonman
author_rank: Super Contributor
timestamp: February 17, 2020, 01:37:28 pm
content: Quote4040A units do not have serial data out; 4040A/RS units do (the RS stands for RS232).

author: notfaded1
author_rank: Frequent Contributor
timestamp: February 17, 2020, 05:56:05 pm
content: Quote from: bostonman on February 17, 2020, 01:37:28 pmI know that but I can show the front of mine it says 4040A/RS and believe me it doesn't have a working serial interface in it. They used the same case for both types during the period mine was made. Mine also does have the RS-232 port on it but it's totally empty of connection on the back inside. When I bought it I thought it had a real RS-232 DB25 since it's on the back of it.Bill

author: bostonman
author_rank: Super Contributor
timestamp: February 17, 2020, 06:01:44 pm
content: QuoteI know.... I worked there for over thirteen-years. It's possible that unit was worked on by me because I worked on every unit that was returned for repair.

author: notfaded1
author_rank: Frequent Contributor
timestamp: February 17, 2020, 06:10:57 pm
content: Quote from: bostonman on February 17, 2020, 06:01:44 pmI wish I knew how to get more info from mine. It would be pretty wild if you did work on this one. My next step would be to take apart the cage that holds the power supply in the back and test all the caps. That's one thing I could fix. The main issue I have is I don't have any documentation that tells what the correct voltages on the strip of power connections are supposed to be. I don't have it front of me right now but there are a bunch of connection screws in a row next to the main power cage in the back. The cage is a black screened metal box.Bill

author: bostonman
author_rank: Super Contributor
timestamp: February 17, 2020, 06:13:27 pm
content: QuoteDoes it have a round inspection sticker over one of the panel screws or a white rectangular tag on the front with the unit S/N and other info?

author: notfaded1
author_rank: Frequent Contributor
timestamp: February 17, 2020, 06:15:43 pm
content: Quote from: bostonman on February 17, 2020, 06:13:27 pmIt has a round inspection sticker.

author: bostonman
author_rank: Super Contributor
timestamp: February 17, 2020, 06:17:46 pm
content: It should have initials then. If not my initials, it would be the initials of someone who worked on it, but I would have overseen the repair.

author: notfaded1
author_rank: Frequent Contributor
timestamp: February 17, 2020, 06:38:21 pm
content: Quote from: bostonman on February 17, 2020, 06:17:46 pmI'll check the markings tonight when I get back home! That would be really wild.

author: bostonman
author_rank: Super Contributor
timestamp: February 17, 2020, 06:42:12 pm
content: That's a 5030 based unit (the module inside the unit). I repaired every 5030 based unit exclusively throughout my career.If it didn't have a sticker on it, then I'd still be able to tell my work by looking inside. I routed wires and stuff a certain way to make it nice and clean. So every unit had my marking one way or another.

author: notfaded1
author_rank: Frequent Contributor
timestamp: February 20, 2020, 12:11:17 am
content: Post of pic from my Datum 4040A for bostonman. Do you recognize the stamp?Bill

author: bostonman
author_rank: Super Contributor
timestamp: February 20, 2020, 01:57:17 am
content: Wow, that's an old unit.That round sticker was used until maybe 2003, however, from what I remember, until then, from 1998 on, the person who sealed the unit would print their initials on the sticker.That sticker appears to be a special 'FTS' (large F and small TS) stamped sticker. I spent time trying to think of employees with TS and tried to phone the old phone directory (I have it somewhere), and then realized, the letters spell FTS (Frequency and Time Systems). FTS was the name of the company until the late 90s, it became Datum (hence why the sticker reads FTS and Datum) sometime in the late 90s until around 2003, got bought out (or merged) with Symmetricom, eventually Microsemi, and finally MicroChip.If you really want to know how old the unit is, remove the cover and look at the sticker on the Cesium Beam Tube. The serial number should read something regarding the year it was manufactured.What I can tell you is: that cover hasn't been removed since the latest year of 1999. If it had been, it would have had one of three initials on it; the most likely would be mine. In fact, even if it had initials other than mine, I may have worked on it, but given it to someone to test, so they used their initials upon sealing the unit.If you have anymore questions, feel free to send a private message.

author: notfaded1
author_rank: Frequent Contributor
timestamp: April 14, 2020, 12:44:21 pm
content: Quote from: bostonman on February 20, 2020, 01:57:17 amGood Morning Bostonman and anyone else! Here's the picture of my units tube and LO. I ordered and I think being delivered today is this I'm going to use to breakout the 15 pin monitor port on my Datum 4040A. Now that I have the manual for the 4065 thanks to fellow timenuts here on eevblog I'm in MUCH better shape! All of the units contain the same basic 5030 assembly. Mines exactly the same, for the most part as in the 4065 and 4060/S24. I think since my unit is older without built in db-25 RS-232 output (well it has connector but nothings connected to it o.O) I'm hoping I'll get signal on some of the PIN's like in the 4065 manual. One thing I don't really get is the second page of the Table 2-1 Monitors and Indicators. It's a DB-15 connector yet on page two it lists connector 20 and 21? The first page with 1 through 12 makes sense. I suppose I'll have to just try them all and see.BillBill

author: notfaded1
author_rank: Frequent Contributor
timestamp: April 14, 2020, 12:46:37 pm
content: Here's the Monitors and Indicators pages... it's a DB-15 connector so how does the second page make sense?

author: notfaded1
author_rank: Frequent Contributor
timestamp: April 14, 2020, 12:50:08 pm
content: More of my pics for Bostonman, Ed, and anyone else...

author: bostonman
author_rank: Super Contributor
timestamp: April 14, 2020, 02:12:36 pm
content: I'll need to either read through the messages on what you're trying to accomplish, or get a better understanding of what you need.If I remember correctly, that connector pin list is for the connector on the DB15 on the rear of the 4065. If any thing is connected to that connector, it's 4065 stuff. I think the connector the manual is referring to is the large 36 () pin connector on the side of the 5030 (I'll need to look further later today or once I understand what you need).For that, you need a "special" box (i.e. "Monitor Box") to connect that reads specific signals on the 5030. Without the box, it would take some tinkering to read individual signals. In fact, if you need to make any adjustments, you would need to connect to multiple pins simultaneously to do something as simple as centering the oscillator.Most likely the Monitor Boxes don't exist anymore because probably back in 2007 Symmetricom ceased repair/support on all 5030 type units. Now MicroChip (formally Microsemi, formally Symmetricom) has ceased repairing all Cesium units pre Cesium III (Cesium III would be 4310, PRS 4400, PRS 4500, CS 4000, and the Agilent 5071 that MicroChip owns).When I worked there, sometime around 2004, the company began implementing 5S and Lean Manufacturing (I'm getting chills just thinking about it), so they began throwing anyway that wasn't used in the last 5min. So anything that was considered not used (5min is me being sarcastic) got set aside, if it wasn't used for X months after, it got thrown in the trash. Once 5030 based units stopped being worked on, employees began leaving, and new employees came in, that technology was forgotten about. So people would pick up something and ask what it was, I'd tell them, and they would throw it away because it wasn't needed.

author: notfaded1
author_rank: Frequent Contributor
timestamp: April 14, 2020, 02:31:06 pm
content: I think I may be able to get one of these FTS 6006. Is this what it looks like? I'm just trying to get some debug info from the 4040A since it's serial port isn't connected at all inside. The monitor port is a DB-15 connector on the back. Here's a pic of the back of the DB-25 inside. Here's a pic of the monitor port as well.Bill

author: bostonman
author_rank: Super Contributor
timestamp: April 14, 2020, 02:34:11 pm
content: I made an error.I needed to look at it again. This is going off the top of my head without additional information, and thinking further.That 15 pin connector should be for relay outputs. The DC/DC low voltage supply (not the black Abbott, the other one) provides replay contacts such as locked and unlocked.In a 4065A () that larger connector that is listed in the manual has signals on it. I haven't worked on one of those in years, and know a time existed when they had the same shell with a 5045 which eventually changed to a 4201 (but was nearly identical).Differentiating units was nearly impossible unless you knew what to look for, and even then, unless I removed the cover, I couldn't tell you what was inside. Our "documentation" would take hours to figure out what features each unit had.It was easier for me to remove screws and look.

author: bostonman
author_rank: Super Contributor
timestamp: April 14, 2020, 02:35:42 pm
content: Oops, I replied to your message just before you already typed a new one... see my reply above.Yes, that's the box.I highly recommend NOT making any adjustments until you're sure you need to. If you mess up one thing, you'll need a hell of a lot more equipment than just that box.

author: notfaded1
author_rank: Frequent Contributor
timestamp: April 14, 2020, 02:38:15 pm
content: I haven't adjusted anything. It just won't lock that's all. I do get a signal out of it from the outputs. I'm hoping the connection to the DB-15 monitor port will get some info like the manual says. There isn't any 4040A manual except the user manual (which tells you basic stuff that doesn't help) so I'm going by the 4065 manual because it has MUCH more info and uses the same exact 5030 that's in my unit.Bill

author: notfaded1
author_rank: Frequent Contributor
timestamp: April 14, 2020, 02:43:04 pm
content: Here's the 4060 manual I've been using too:https://www.eevblog.com/forum/metrology/fts-4060-manual-available-for-download/It is exactly like my unit and seems to relate a LOT to my 4040A. Thanks to Corby aka 5065AGuru. My unit has the 5030 and exact same boards in it listed in the 4060 manual. I've just been unable to get any usable troubleshooting data from it because the DB-25 does nothing... so it's going to be me falling back on the DB-15 monitor port and hoping there are signals like from the 4065 manual. I'm also hoping to get the FTS 6006 from a fellow timenut here on eevblog.Bill

author: bostonman
author_rank: Super Contributor
timestamp: April 14, 2020, 02:46:52 pm
content: Read my message above about the relays.Those manuals got hacked too. Too many units had special features for individual customers. So a unit would have say a 1PPS output where as an identical 4060 or 4065 didn't. The manual may or may not even talk about the 1PPS, or an addendum was supplied with the manual.In the late 90s and very early 2000s, the 5030 and 4201 based units became very confusing very quickly.As for not locking, yes, that box is somewhat worth it if you can get it cheap enough. Once you get it, If you find say low tube signal (which you need a low noise pico amp meter for), then there is very little you can do.You may need to check the 9GHz amplitude in which case you need a spectrum analyzer. If that's low, then the multiplier could be junk (those multipliers had a history of failure). The EM voltage is already at the maximum of -2200.

author: notfaded1
author_rank: Frequent Contributor
timestamp: April 14, 2020, 03:23:53 pm
content: Quote from: bostonman on April 14, 2020, 02:46:52 pmI'm hoping my unit has signals on some of the PIN's vs just the relays like the 4040B had. Since it didn't have any DB-25 connection I'm hoping I can get something from some of the PINs besides a switch like the 4060 manual says it had. Like Ed said... it's hard to imagine they left users with nothing at all to monitor their units. It's obvious the later 4040B/RTS models maybe just mirrored the front display LEDs on the back with relays since it had a full blown RS-232 serial interface on it. I'm hoping, like I said, the monitor on the 4040A has something besides high or low on some of the PIN's. I'm going to find out very soon either way. If I'm really lucky I'll get the FTS 6006 and will be able to interface with the lower level larger multipin connector inside the 5030 which has a LOT more info on it.B

author: bostonman
author_rank: Super Contributor
timestamp: April 14, 2020, 03:27:33 pm
content: All you need to do is stick a piece of wire in each pin and measure with a meter.Then you can tell instantly whether you can measure any cesium signals. Like I said though, that DB15 should only be relays and probably only has three wires going to it:NO, NC, and common.Maybe they had two sets of relays back then too, I don't remember. Relays was something I never needed to measure.

author: notfaded1
author_rank: Frequent Contributor
timestamp: April 14, 2020, 03:28:38 pm
content: If I'm really lucky then the monitor port PIN 9 should tell a lot about the tube right?

author: notfaded1
author_rank: Frequent Contributor
timestamp: April 14, 2020, 03:35:51 pm
content: I mainly just want to figure out if the tube it's the tube or it's not first. If it's the tube then I have some nice replacement parts for other owners and a really really nice 10MHz 1000B with very low noise.

author: bostonman
author_rank: Super Contributor
timestamp: April 14, 2020, 03:38:07 pm
content: I'm not trying to sound mean, but these are identical discussions I had for several years with management.They'd ask me the ONE thing to look for when a unit didn't lock because they wanted to train new hires with no experience. Management though they'd get a new hire up to speed in a few days.Yes, that number will reveal "a lot" about the tube. If it's low (which I'm 99.99% sure it will be), then it will narrow it down to: a bad oscillator, a bad low order multiplier, a bad high order multiplier, a bad tube, a bad high voltage supply, or one of the circuit boards (which most likely it's not).

author: notfaded1
author_rank: Frequent Contributor
timestamp: April 14, 2020, 04:24:19 pm
content: Another thing the manual doesn't go into is what are the connections on these for the power? Do you remember at all what the order of these are supposed to be at all? It sure would be nice if I had just a bad cap in the main PS or something and one of the voltages was low or something. I haven't taken the whole PS apart and tested all the caps yet.Thanks,Bill

author: bostonman
author_rank: Super Contributor
timestamp: April 14, 2020, 05:02:06 pm
content: It may have a bad cap, but not likely the cause.Where are you located? We can exchange emails to simplify this too because there is lots to cover.

author: notfaded1
author_rank: Frequent Contributor
timestamp: April 14, 2020, 05:46:05 pm
content: Quote from: bostonman on April 14, 2020, 05:02:06 pmI'm in Scottsdale Arizona and am pretty much an early bird usually. I work 5AM to 1:30PM M-F but as you can see have access from work to at least check eevblog ;^}It appears the bottom brown white black are green coming from the main power input on the thicker wires. Then there's all those red and black small wires which I assume are probably different DC voltages coming off the main PS. I purposely didn't mess with anything inside as I was afraid I might do more damage than good until I had a much better understanding and knowledge of what I was working with. I've learned a LOT since then and have some semi similar documentation now as well thanks to fellow eevblog members. I'm glad you contacted me. I knew messing with some things would be worse than doing nothing.I found some other great info and pics here:http://www.prc68.com/I/FTS4060.shtmlB

author: bostonman
author_rank: Super Contributor
timestamp: April 14, 2020, 10:42:04 pm
content: You mentioned possibly bad capacitors. Your unit is older than when I worked on them, so it could possibly have bad capacitors, but it's unlikely.I know several common failures, but most of the design is so old that lots of power was wasted. If I remember correctly, the Abbott power supply took AC in and produced 28VDC (or maybe 30 - 34 depending on which unit you have based on "dash" condition". That voltage went into a low voltage power supply that produced 24V to the 5030. The A/B/C power supply produces 5v, 15v, and -15v, along with the EM and ION pump voltages. After the 15v and -15v go into a regulator that produces 12v and -12v where needed.The 5030 has two connectors (ignoring the RF connector). One is a 9 pin (only two pins) are used. This is your 24V in. If you have 24V at that connector, don't waste time on anything before that because all you need is 24V. The other connector is the one that would go to the Monitor Box. This has inputs and outputs to open the loop, change the control voltage manually, etc...If I remember correctly, you don't need that large connector for the 5030 to lock because the default electronics will have the proper settings for locking.If you're questioning voltages on the 5030, I can give you an idea on where to measure general voltages. If you get voltages in two places, you can rule out your thoughts on bad capacitors. Again, the caps could be bad, however, the unit isn't going to lock due to noisy capacitors.During my years, I've worked on every circuit on every board in the 5030, worked on oscillators in depth, and was always involved in diagnosing bad tubes.If you want, send a PM to me and we can exchange emails. Maybe talking on the phone will be easier, but I'd be doing lots of it from memory, so you'd need to be bare with me.

author: bostonman
author_rank: Super Contributor
timestamp: April 14, 2020, 10:47:46 pm
content: Can you do me a favor?take a few pictures of:The connectors from the inside so I can see which wires are connected to themThe rear panelThe Front Panel

author: edpalmer42
author_rank: Super Contributor
timestamp: April 14, 2020, 11:00:28 pm
content: Quote from: bostonman on April 14, 2020, 10:42:04 pmThere's a large thread here where an owner of a 4040A discovered that bad capacitors in the 5045 Cesium module prevented locking. I have a 4065A with the same module and my unit has developed the same problem. So, after 20 years, lots of weird things can happen.QuoteI, for one, would prefer if this conversation stayed public. There is so little public information on these units that any crumb of data is eagerly and gratefully received.Ed

author: bostonman
author_rank: Super Contributor
timestamp: April 14, 2020, 11:06:12 pm
content: QuoteThanks for the input, however, different capacitor problem. Many (and I'll emphasize that word) 5045/4201 used capacitors that blew up. 100s of units came back for not locking, I'd open the A/B power supply, see all the capacitors blown, and replace the power supply.

author: bostonman
author_rank: Super Contributor
timestamp: April 14, 2020, 11:17:35 pm
content: Also, just to elaborate, older 5045 units had capacitor issues too, but not like the one I referred to.The older capacitors would fail by leaking from the bottom, sometimes shorting the layers of the PCB. The issue I referenced was junk (Xicon I think) capacitors exploding from the top.In older units, maybe one capacitor would leak from age and that could short the layers. In the newer units (within 3-4 years) the Xicon caps would explode from the top. Not just one or two, every single capacitor. If ONE capacitor was a different name brand, then that would be fine, just the Xicon would be blown.

author: edpalmer42
author_rank: Super Contributor
timestamp: April 15, 2020, 03:13:38 am
content: Quote from: bostonman on April 14, 2020, 11:17:35 pmThese ones seem to be silver Sprague 672D. There are two blue ones with the 'shield' logo of Nippon Chemicon. So far, leakage is minimal. I haven't found any board damage because the capacitors hang upside down and they're spaced away from the board. My unit dates from 5/25/00 according to the sticker. The middle initial is a bit hard to make out. Maybe GSH.Ed

author: bostonman
author_rank: Super Contributor
timestamp: April 15, 2020, 03:35:03 am
content: QuoteYes, GSH is correct. I know the person who worked on that unit - and he's still with the company - as a "manager".Sounds like you have the thru-hole A/B power supply. You may also be referring to the date on the inspection sticker and not the manufacturing date. After a unit was repaired, we'd place a round tamper resistant sticker (that was easy to peel off) over a screw, and place our initials and date on it. The real way to tell when the unit was built is to look at the tube serial number (and maybe the serial number on the unit itself).The thru-hole supply (07957 if memory serves me correctly) had many larger capacitors, silver and blue, and the caps had very little room so they were packed tightly. When those went, they'd have a fish odor, but again, they'd need to fail badly in order to cause locking issues with the cesium. If bad enough, I think they'd cause alarms because a voltage would go out of range, however, those were probably 'minor alarms'. As I mentioned, some of those capacitors got bad enough to burn the PCB (and I think it was a seven layer PCB). So layers would short to each other.The surface mount version came around the 2000s or very early 2000s. It was nearly identical, only with surface mount components making much more room for the aluminum caps that became Xicon.After a while, the approved vendor list included Nichicon, but, at that point, the company already purchased five trillion Xicon and insisted on running out stock even though they were known to explode; thus making room for many more failures years later.

author: notfaded1
author_rank: Frequent Contributor
timestamp: April 15, 2020, 06:29:58 pm
content: Quote from: bostonman on April 15, 2020, 03:35:03 amI bet you just loved this... I suppose it meant a LOT more rework and repairs for the repair shop. Symmetricom probably liked this... I'm not sure many others did. I'm going to take more pictures for you soon. Time to get the beast back on the bench!

author: ArthurDent
author_rank: Super Contributor
timestamp: April 15, 2020, 07:58:16 pm
content: Quote from: notfaded1 on April 14, 2020, 12:46:37 pmHere's what the inside of the FTS6006 monitor/control unit and the 37 conductor cable looks like.

author: bostonman
author_rank: Super Contributor
timestamp: April 15, 2020, 10:45:57 pm
content: QuoteI'm curious, how did you obtain one of these? I don't believe FTS sold these separately.

author: ArthurDent
author_rank: Super Contributor
timestamp: April 16, 2020, 12:55:19 am
content: Quote from: bostonman on April 15, 2020, 10:45:57 pmI've got 4 of these FTS 6006 units over the years, only one cable, and no cesium beam standard. I have had S/N 04 (which I sold) and have S/N 01, S/N 023, and S/N 1007 which makes me wonder how many were made.Other FTS units I have are a 4 input "multichannel phase comparator" FTS 6101/001 S/N 121 plus 2 prototype looking units that may be time interval units marked FTS 6102 S/N 023 and 037.

author: bostonman
author_rank: Super Contributor
timestamp: April 16, 2020, 01:06:43 am
content: I'm baffled how those boxes made it out of the facility. In any case, those phase comparators are not anything special. They convert the frequency to DC, and provide a voltage to a chart recorder. If in auto, they switch channels every so often by detecting which channels have a frequency on them.I don't now what a 6102 is. Can you post a photo?

author: ArthurDent
author_rank: Super Contributor
timestamp: April 16, 2020, 05:00:15 am
content: Quote from: bostonman on April 16, 2020, 01:06:43 amI had tried the phase comparator and it works as you described.Here is what I found out about the 6102 units. I.C. date codes indicate they were made in 1987. I had quickly checked the circuit board to see if I could figure out what goes on and have a photo of the input section of the circuit board. There are 2 floating BNC inputs (A & B) that go through isolation transformers to buffers then to a phase detector. From the parts used it appears the circuit might be usable from near d.c. to about 100Mhz. The phase detector gives a d.c. voltage proportional to the phase difference and seems to be followed by RC low-pass filtering feeding the op-amp, which seems to make sense. There are 2 output BNC connectors marked ‘A-B’ and ‘analog’There are also two LM211 voltage comparators that may be used to trigger the 8-digit counter chip that drives the front panel display. You can select 3 of the 8 digits with a switch and apparently the numeric value of that 3-digit number is converted with a 12-bit D-A converter to drive a recorder or whatever. Four decade averaging periods are also selectable. There is also a 25 pin ‘D’ connector on the rear marked ‘controller’ but I’m not sure what that does or if it is necessary to use the unit as a comparator.One of the front panels was made from a plate that has holes drilled for 6-32 screws to be used as a back plate so I assume these were engineering samples and they weren't too concerned about parts and used whatever was on hand.

author: bostonman
author_rank: Super Contributor
timestamp: April 16, 2020, 02:02:50 pm
content: I know what those are too..... I'll explain more later, but they are basically the 6101.They were confusing to use, and the red triangles on top had to do with parts-per-billion and got selected by moving one of the two knobs.I'll give thought to their function, but, to be honest, whenever I asked questions about them, it seemed others who used them couldn't answer the questions. They were exclusively (maybe used for other purposes before my time) for oscillators. So when I began my employment, I was exclusively repairing, testing, aligning, oscillators. The first oscillators I worked on were the ones in the 4060 in the cesium pictures above, then the same type of oscillator, only different model.

author: notfaded1
author_rank: Frequent Contributor
timestamp: April 16, 2020, 03:03:48 pm
content: From the picture it looks like the cable may be straight through on the D-37 to D-37 cable and since you've got plugged into itself it must be male on one end and female on the other correct?B

author: notfaded1
author_rank: Frequent Contributor
timestamp: April 16, 2020, 03:06:21 pm
content: Actually if it's straight though I can buy a premade cable and not mess with the D-37 connectors.

author: notfaded1
author_rank: Frequent Contributor
timestamp: April 17, 2020, 12:59:46 pm
content: Can you verify it's DB-37 M to F @ArthurDent? I might as well order a cable now since you're sending me an FTS 6006. Pretty neat that's it's serial number 001. The first ones gotta work you'd think.

author: ArthurDent
author_rank: Super Contributor
timestamp: April 18, 2020, 04:04:15 pm
content: The photo I showed is a M-F extension cable.If you make your own cable using connectors with solder pins, plug the two connectors together and make sure that each wire you solder to a connector pin on one side goes to the corresponding pin on the other connector.If you use ribbon cable and IDC connectors make sure you don’t put one of the connectors on backwards.Premade cables might be the best way out.

author: notfaded1
author_rank: Frequent Contributor
timestamp: April 18, 2020, 05:42:37 pm
content: I'm making good headway. I powered it up last night again and this morning took the covers off again. I found both ends of the DB-37 inside...

author: notfaded1
author_rank: Frequent Contributor
timestamp: April 18, 2020, 05:43:25 pm
content: the 5030 end of the cable...

author: notfaded1
author_rank: Frequent Contributor
timestamp: April 18, 2020, 05:52:22 pm
content: pics...

author: notfaded1
author_rank: Frequent Contributor
timestamp: April 18, 2020, 06:49:31 pm
content: The monitor DB-15 is basically useless except for telling you the same thing the LED's on the front tell you. Major and Minor alarms.

author: notfaded1
author_rank: Frequent Contributor
timestamp: April 18, 2020, 07:18:38 pm
content: Video of what the 10MHz is doing:https://photos.app.goo.gl/2rVMtYbkXEzzCvBN9It basically is snapping up and then counting down.Bill

author: edpalmer42
author_rank: Super Contributor
timestamp: April 18, 2020, 08:24:43 pm
content: Is your counter referenced to your GPSDO? Assuming it is, when it's hunting as shown in your video, does the frequency ever drop below 10 MHz? If not, there's your problem. It's looking for the lock signal, but it can't find it because the oscillator is too far off frequency and can't be electrically tuned to 10 MHz so it hunts forever. The same thing happens in a Rb standard.The oscillator should have a frequency adjustment on the side with the connectors. Give it a nudge and see if the frequency sweeps closer to 10 MHz. If it happens to lock, keep adjusting in the same direction for a bit so that you're well into the adjustment range.Ed

author: ArthurDent
author_rank: Super Contributor
timestamp: April 18, 2020, 10:24:27 pm
content: here's the marketing info on the 5030.

author: bostonman
author_rank: Super Contributor
timestamp: April 18, 2020, 10:51:17 pm
content: QuoteNO! Don't do that now, the oscillator is too cold. Let it sit for at least 24hrs before touching the control voltage.

author: edpalmer42
author_rank: Super Contributor
timestamp: April 19, 2020, 12:23:39 am
content: I keep forgetting that we now have someone who's familiar with this equipment. Usually we just have to try stuff and see what happens!Is there an official procedure to open the loop and allow the oscillator frequency to be set while in the chassis or would this normally be done with the oscillator on the bench?Ed

author: bostonman
author_rank: Super Contributor
timestamp: April 19, 2020, 12:40:58 am
content: QuoteI didn't mean to blow up. I was trying to avoid too many cooks and have his Cesium unit go completely out of wack.Yes, adjusting it is simple. It does involve opening the loop, but you either need a monitor box (which he should be getting) or short/open pins (I assume this is how it's done - I've never had to manually tweak logic lines). Also, you need a frequency reference so you know how far off the oscillator is.Your advice wasn't far off because you could just turn at random, but ideally you don't want to do that. If you turn randomly and get the oscillator close enough, and the unit locks, then tweaking it closer to center is easier. So you're not wrong, but he's getting the monitor box, and the unit hasn't been powered long, so I'd prefer he approaches it methodically.

author: edpalmer42
author_rank: Super Contributor
timestamp: April 19, 2020, 12:51:37 am
content: We might both be premature.If the oscillator frequency does cross 10 MHz and doesn't lock, then tuning isn't required and won't help. We'll have to wait and see what Bill says.But wouldn't it be nice if that's all that was wrong!Ed

author: notfaded1
author_rank: Frequent Contributor
timestamp: April 20, 2020, 01:33:49 pm
content: I made some headway and am measuring voltages on the power board. One thing we realized I'm going to have to figure out. My 5030 unit is getting it's power from the DB-37 cable. Many later units got it from the DB-9. Mine doesn't have anything connected to the DB-9. One thing I need to figure out is the pin out of the DB-9 for the power. The reason is because if I hook up the FTS 6006 on the DB-37 then I'm guessing it won't have power any longer. The FTS 6006 most likely doesn't power the 5030. I ordered a nice DB-9 breakout board to help with this and an extension cable for it. I did the same with the DB-15 but that was a total waste since all it is is basically 3 relays. No signals on there to measure at all. When it's doing is frequency thing now like in the video it doesn't really get down to 10MHz. I've seen it briefly try and hit right under 10 but then snap immediately back up to the high frequency again and start counting down again. It's trying to do it's thing. The voltage looks pretty good although I found out the -18 V on the CPU board is reading more like -20 V. Regardless what happens with this it's already been a fun journey. If I can't get this one going I'm always looking for other units.On the Rb front I have another GPS disciplined Rb in the works that's a Spectratime SRO-100 based instead of the SRS PRS10 one I posted about recently. I'm excited about it because it does something the PRS10 doesn't do... it saves it's disciplining variables in non volatile memory. Another difference is this one is disciplined with Ublox LEA-8T instead of LEA-6T like the SRS PRS10. I love the idea of GPS disciplined Rb. It's really more practical than the Cs and much easier to work with.The more I experiment with these Rb and GPS driven oscillators the more I'm finding out how variable they all are... once you get into ns and ps there's more going on than most people usually see. I guess that's what it's all about though?

author: ITDH
author_rank: Contributor
timestamp: June 24, 2025, 02:03:02 pm
content: Hi –my first post here, I'm hoping for some help with a Datum FTS4040A ("Later version" with RS232) - I believe the correct model number is FTS4040A/RSThe units ROM is 5045A V2.00, x0/14/1999 ("x0" as the ROM label was misaligned when printed so the first digit of the ROM Date code is missing)...I took a risk and acquired the unit after it sat unused after an unsuccessful PSU ReCap repair - the PCB was damaged during the Recapping resulting in open circuits on the PSU PCB). I believe I have repaired the PSU with the +24V, +/-15V and +5V rails looking OK.I've not yet been able to confirm operation of the floating Ionzier or CS Oven supply rails as the unit will not power up the Cs Tube section (The Green “AC Power Available” & “Red "Major Alarm” LEDs are lit).I've been told that the unit was working OK with a believed decent Cs Tube (I'm hoping) before the unsuccessful PSU ReCap repair – The unit would occasionally indicate “Minor Alarm” – but the unit stayed Locked – the “Minor Alarm” indication was believed due to the failing PSU rails.However after repairing the PSU section, unit now is now “Dead” with Green “AC Power Available” & Red "Major Alarm” LEDs are lit – the unit never starts the “Initialization” process.Notes:-1. I've confirmed that the Cs Tube has apparently a good Vacuum – with the Ion Pump current below 0.5uA (measured at Ion Pump PSU current monitor terminals) –400uV, The current measures the same with and without the Cs tube connected to the PSU HV – Ion Pump HV output measure's about 3.2KV2. 90MHz is sent to mainboard (from the RF block on Cs Package assembly) – so 10MHz OCXO and x9 Clock multiplier section is working.3. I tried to communicate with the unit using Monitor3, but with no luck – I used PuTTy and see the following message repeated about every second:- "ERROR 03", I don't seem to be able to send any commands to the unit over RS2324. My unit is set to 9600 Baud (not 2400 Baud as suggested in 5045A Manual)5. The MCU does not seem to try to initialize the ADC, DAC or the troublesome STEL1173 NCO, I've never seen any activity on the ADC “Busy” Pin TP4 or any attempt to configure the Cs Gain DAC or Configure the STEL1173 NCO etc.As the MCU does not try to configure or read-back the ADC it cannot be a problem with any of the ADC “values” (PSU Rails, Ion Pump CS tube values etc) causing the "Major Alarm"It seems that the MCU section is partially dead – BUT the MCU is able to send a repeating “Error 03” Message over the RS232 port – every 1 Second or so (is there a watchdog timer?) – but the MCU NEVER trys to communicate with ADC / DAC / NCO etc...One oddity, the Q output pin on U35 (74HC74) that provides the 45MHz clock to the NCO / DAC was short circuited – I've replaced the IC and now have a clean 45MHz to the NCO / Clock DAC section.So maybe during the previous repair attempt there was an ESD discharge to the PCB or over-voltage on the 5V rail... who knows, its hard repairing a unit thats already been worked on before... its a risk I've taken with eyes open...Does anyone know what the repeating "ERROR 03" over RS232 indicates? I don't believe its related to any of the Cs tube / system values as the ADC is never configured or read back by the system MCU....Many thanks in advance...

author: ITDH
author_rank: Contributor
timestamp: June 29, 2025, 03:48:11 pm
content: Update on my unit repairs...I realized I might have answered my own question in my original post – where after the PSU repair the unit appeared "Dead" with repeating ERROR 03 over serial port every second or so - which I mentioned looked like a potential MCU Watchdog timer issue...Unfortunately I'm not currently able to power up the unit as one of the first things I did was remove the STEL1173 NCO IC and I'm waiting for a PLCC socket to arrive from Mouser (rather then directly soldering the replacement IC to the PCB) – I'm now pretty sure the original part was OK, but with the part being so unreliable I might as well fit a PLCC socket to the PCB.Working “Blind” I started to trace out the MCU Reset circuit and did indeed find a Watchdog timer circuit- but while drawing out the circuit I found two logic IC outputs (Non Tri-State parts) connected together! I did earlier find a PCB design error on the PSU section so I was not certain it was not a second PCB design error – but then I did have a suspected watchdog timer issue...I removed the logic IC's but still had a short on the PCB... so I removed the PCB from the chassis (as far as I know this is the first time the PCB has been removed since production) and found a solder bridge between two PCB Vias on the PCB underside!!!The solder bridge seems rather “Solid” so not something that could be intermittent... I don't understand how this PCB / unit could have ever worked, this looks like a production issue.Some observation after drawing out the Reset circuit:-Jumper “TB2” will disable the Watch Dog Timer circuitTP18 (next to the Serial port 25W D Socket) is the output of the WatchDog Timer circuit – it should be “High” for normal operation (not pulsing Low = MCU Reset).I've not tested the board yet (waiting for the PLCC Socket) – but I'm pretty sure that the shorted Vias ware the cause of the “Dead” unit...When Time allows I'll draw up the MCU Reset circuit schematic – I now plenty of the units circuits (PSU section etc) drawn up on paper to understand how the unit should work...After all this time and effort – I hope my Cs Tube is OK...If anyone needs help with there unit then I'm sure I can offer some advice based on the time spent working on my unit so far...Mouser parts should arrive this week – I've also order a Push Button Switch to move the Storage / Operate Switch to the front from the Rear panel where its currently inaccessible when the unit is Rack mounted...To make it easier for me to repair the unit without service manual & schematics I've “cleaned up” and simplified the unit up by removed the Telco DSI interface & and Clock Buffer / Divider boards (I only need a single 10MHz Clock Output with lowest Close-in Phase noise) – I will eventually take this 10MHz directly from the OCXO with a custom Buffer PCB.Bostonman:-Thank you for very much for your reply to my PM, I'll take some pictures and post here once I've put the unit back together... but I don't see any “Inspection Stickers” on the unit... inside or out.. Its currently completely pulled apart ATM, so I'll take pictures once I've put it back together again...I traced out the the relevant PSU sections on the PCB so pretty certain that despite it being 6-7 layers all is now good... the 5V, +/- 15V and 24V rails look good – without a fully operational MCU I've not been able to confirm the Cs Tube supply rails (according to the user manual, the MCU only enables the Cs supply rails once the VCXO Heater Oven current has dropped to a “warmed up” level – apparently to reduce the Max PSU power demand requirements.My current "best Guess" theory as to why I'm seeing a repeating ERROR 03 message is that this is the first Error message reported by the MCU (with the Cs package shut down) – the unit is being Reset by the Watch Dog timer before the MCU has a chance to report other Error messages... Also, why I have no communication with the unit with the “Monitor3” program....

author: bostonman
author_rank: Super Contributor
timestamp: June 29, 2025, 04:23:27 pm
content: Most likely the error 3 doesn't have anything to do with the watchdog timer circuit.

author: ITDH
author_rank: Contributor
timestamp: June 29, 2025, 04:35:48 pm
content: Yes, sure, I suspect that ERROR 03 is just the first error message being reported by the MCU - (related to the Cs Tube being shut down and not operational) - then the WatchDog Resets the MCU and the MCU is now caught in a repeating "Reset" loop - only having the time to report the inital ERROR 03 message - then it gets Reset again...The MCU has no method to detect or report on any on Watchdog timer circuit fault ...

author: bostonman
author_rank: Super Contributor
timestamp: June 29, 2025, 04:45:49 pm
content: If you're getting an error 3 upon powering the unit, then you have bigger issues.The unit doesn't initiate error messages until it attempts to lock (somewhere >12min - depending on the type of unit). It may generate errors such as voltages being out of range prior to the lock attempt (these types of errors were far and few, so I don't remember), but the tube is cold for the first 4min, so it will not have any tube alarms until it attempts to lock or locks.

author: ITDH
author_rank: Contributor
timestamp: June 29, 2025, 07:55:06 pm
content: Oh Great..I was hoping I was over the worst with this unit - now I'm really eager for the Mouser order to arrive so I can mount the PLCC socket and test the unit!!

author: ITDH
author_rank: Contributor
timestamp: July 02, 2025, 01:16:54 am
content: I mounted the PLCC socket today - and removed the PCB short circuit in the watchdog timer circuit - but still no change in operation as Bostonman suggested!I suspect that the PCB experance an over voltage during the orignal PSU repairs - this would explain the blown U35 74HC74 - this IC divides the 90MHz clock by 2 (45MHz) which clocks the NCO / DAC section and is the fastest operating CMOS logic Gate on the PCB.I dumped my ROM and its blank (FF) from 0x0000 to 0x6FFF - with code starting from 0x7000 to 0xFFFF, can anyone confirm if this is correct?First line of ROM code from 0x7000 (ROM from 0x000 to 0x6FFF is all FF)56 45 52 53 2E 1A 10 B7 4E 00 B7 4C 00 VERS.01....N..L.My ROM (ST 27C512) is:-5045A V2.00P/N 08896 Rev Kx0/14/1999 (x= I cannot read the first digit of the date code).

author: ITDH
author_rank: Contributor
timestamp: July 02, 2025, 01:22:36 am
content: Looking at the signals on my PCB - I believe that the ROM code starting from 0x7000 is correct as A12 is always High... (A12 never seems to go Low)

author: edpalmer42
author_rank: Super Contributor
timestamp: July 02, 2025, 01:49:27 am
content: The ROM in my 4065A ( a 5045A with a different chassis/display around it) is V1.9J, dated 07/28/1998, but here's the dump in case it's useful.My unit is also down due to failed capacitors. The physical design of that power supply board is so poor that it's almost impossible to remove the bad capacitors without destroying the board. I'm going to try using ChipQuik to see if it will help. I don't know when that will happen.

author: ITDH
author_rank: Contributor
timestamp: July 02, 2025, 09:59:46 am
content: Hi edpalmer42,Thanks VERY for the ROM dump - it confirms your active ROM Code also starts from 0x7000 so it suggests my ROM should be OK.I don't have a display on my unit - does your have the Blue VFD / Keypad as the unit below?My unit is the FTS4040A/RSHowever they both appear to use the same 5045A Cs "Module"Browsing through the ROM code and there appears to be a "Factory" Test / configuration mode accessible via the RS232Dont worry about damaging the PSU PCB, its quite a simple circuit – I had to track out the relevant circuit sections to repair the PCB damage caused by the previous engineer - It was not his fault, just the combination of the damage done by the leaking capacitors and the rather poor PCB quality, with the tracks / through-hole plating vaporizing if you so happened to glance badly at the PCB!Just one point to clarify – I've seen it stated here that PSU capacitors are in parallel (this is only true for the input “light Blue” Caps) the Caps "Pairs" on the secondary side are on each side of the Yellow inductors, you can see this from your voltage readings where the second “Paralleled” Cap has a slightly lower voltage due to the DCR of the inductor ...I had to bridge the damaged through hole plating / PCB tracks with the leadouts of the new Caps...I'd suggest not leave the repair for too long as the leaking electrolyte really eats the PCB copper tracks causing more damage.I can help you with the repair, if you get stuck then I can draw-up the PSU schematic in CAD... or even better I can repair your PCB and test here..I'd be interested in buying your unit or a “Spares” 5045A Module” if you dont have time to repair it... I believe I have a good Cs Tube...One question, on the second smaller PSU controller board (thats connected to the larger PSU board by the flexible cables) I noticed that there a DIL Socket with a "Resistor header block" installed – is this resistor block matched with Cs tube to “configure” the individual Tube parameters such as the Tube's optimal operating Temperature / Tube Oven Thermistor resistance value etc? - I don't believe that these are defined in the software “service mode” because of the lack of DAC inputs from the MCU to the PSU controller board (which would have allow software configuration of Oven operating temp etc).So if one where to swap Cs Tube, then I suspect that at a minimum you will also need to swap this resistor DIL “header block” - which I suspect comes paired with the Cs tube, then the following questing is do you also need to configure any “factory” software settings in the “Hidden” service mode? - I suspect you might need to...Can the Cs Tube input Gain block (DAC Gain / Numeric Gain) also “Automatically” scale downwards (with a replacement Cs tube with a hopefully higher output signal level) – or does the software only expect to tune these values upwards with a ttypical aging Cs tube?

author: edpalmer42
author_rank: Super Contributor
timestamp: July 02, 2025, 05:30:35 pm
content: Quote from: ITDH on July 02, 2025, 09:59:46 amYes, that's what mine looks like. That particular display is rather worthless IMHO. It's only useful if the unit is running 24/7 which isn't usually appropriate for a hobbyist who's trying to squeeze as much life as possible from a unit on its last legs.QuoteCorrect. I don't know how many 'wrappers' were used with the 5045A, but there's at least two.QuoteThanks for the heads-up. I might have just connected them in paralled.QuoteSorry, I have no idea on any of this. Maybe Bostonman knows.FYI, I've attached a few pictures of my 4065A. The 'Status 1' display shows the format of the more useful screens and the values for my unit when it was working. The shot of the inside shows the 5045A with all the surrounding 'stuff'.

author: ITDH
author_rank: Contributor
timestamp: July 04, 2025, 11:02:40 am
content: Today I recieved (3) STEL-1173/CM's from a Chinese seller and before trying them on my PCB I quickly probed them just to confirm that they are what they say say on the package (not some random remarked parts).To confirm the correct parts,using a DMM I probed Pin 1 (VSS) and Pin 36 (VSS) to confirm that they are connected together as IC "Ground's" (its unlikely that other IC's are internally bonded like this), thankfully they appear to be "Orignal" parts. However during probing I noticed that one IC had "hard" shorts between pins and upon closer inspect under a microscope I found what apeared to be tiny Tin whiskers bridging pins - the tin whiskers used the PLCC package moulding "flashing" as the path bridging between adjacent pins... The whiskers where so tiny you could only see them under a Microscope - or if you angled them in the light you could just about make something was "odd" between the shorted pins...So I wonder if the high failure rate of these parts was "simply" due to Tin whiskers or was I just "unlucky"?Its interesting how the Whiskers used the "sharp" surface of the pastic moulding flushing "joint" as the path to grow between the pins, they where "embedded" in the flushing and where so tiny you could only see them with the aid of a microscope...To me it almost seemed that extra solder residue had builtup between the pins (caught on the moulding flashing) and the wiskers grew from this residue.. really hard to say...Maybe something - maybe nothing... coming form China who can tell the history of these parts...

author: bostonman
author_rank: Super Contributor
timestamp: July 04, 2025, 02:06:03 pm
content: QuoteYes, those resistors are matched with the tube. If the tube is replaced, the nominal tube settings need to be stored in the firmware; else it remains in minor (or major?) alarm.I don't remember if the customer has the option to store the 'nominal values' because our monitoring software was always in factory mode, so I don't remember which options are unavailable to the customer.

author: ITDH
author_rank: Contributor
timestamp: July 08, 2025, 04:55:37 pm
content: I've not had much time to work on my unit - but I'm leaning towards a potential issue with the SRAM - this would explain the very low level of MCU activity.I removed my units SRAM HM65764N-5 (some Servo boards use the CY7C186) - and I tried to test in in a T48 Programmer / Chip tester. The T48 does not have a HM65764N or CY7C186 in its device list, but does have the standard 6264 SRAM type - however from what I can see they only differ with Address line ordering (which from my understanding should make no difference when testing as the Address line order sequance is maintained during R/W) - the SRAM fails the T48 chip testing... but I could be mistaken about the importance of Address line ordering... or maybe there are some other differences (acess Speed / RAD hardness should not be an issue) between the 6264 / 65764 parts.I did test the 65764 with the aid of a Huntron Tracker - and SRAMS Address Pin A0 does look different to the other Address lines. The Huntron Tracker is a great tool for at looking at Logic IC's I/O pads (IC internal ESD protection diodes) etc...Interestingly, Error 03xxx indicated Memory error on the original Macintosh Computers (the rectangle units with internal B/W monitor) – I wonder if the software programmer was a Macintosh fanA note of caution about using the Huntron Tracker with newer small geometry (Low Voltage) CMOS IC's - its high output Voltage / Current stimulus test signal can damage LV CMOS parts - or IC pads that don't feature ESD protection or have limited ESD protection (such as VCO input pins on some IC's etc.) - so use with caution...If the SRAM is bad then it does add more support to my theory that the Servo board experienced an over voltage event on the 5V rail due to the failed PSU repair.I dumped the data from the Xicor 2716 Flash memory and its a pretty much a repeating 3 – 4 byte pattern... I would have expected more factory configuration Data?

author: bostonman
author_rank: Super Contributor
timestamp: July 10, 2025, 02:15:58 am
content: QuoteWhere did you conclude an 'error 3' is a memory error? That's a Zeeman issue (as I already mentioned to you before).I'm not sure I can follow your findings/conclusions because they seem to be all over the place.

author: ITDH
author_rank: Contributor
timestamp: July 10, 2025, 12:30:38 pm
content: Sorry if I appear to be jumping all over the place – I very much appreciate your help (I'm very much a novice here), however without schematics it becomes a process of trying to better understand the design – decrypting the inner workings of the unit, so I'm very much having to learn as I go here...WRT "ERROR 03" I was making a light hearted comment thatIFmy units issues are due to a failed SRAM, then coincidentally Error 03xxx was used on the first MAC's to indicate a RAM errorAs I mentioned previously in my earlier posts - I now really believe that my Servo PCB has been damaged by over voltage on the 5V rail (Maybe the SMPS regulator became unstable due to the OC / failed bulk filter capacitors on the 5V output) - the feedback for the primary SMPS controller is taken from this 5V logic rail, it can be expected that the Controller Loop Gain will go completely nuts and unstable if filter caps are effectively open circuit (With a Voltage feedback SMPS Controller IC, the Filter capacitors on the PSU rail are effectively in parallel with the SMPS Controller Loop filter (the SMPS controller is a VOLTAGE feedback controller) so indeed the main bulk caps set the primary feedback Pole - so I'm expecting more failed parts IF my suspicions are true...I suspect I might also have a failed 74HC14 – its inverting but it seem's to have lost its Schmitt Trigger input feature if that makes any sense? As crazy as this seems, I'm saying this as the “crude” R/C oscillator section based around U14 - Pins 10 and 11 is not oscillating – the input is “Self biased” around VCC/2 (as you would expect with a basic ressitor biased inverter without Schmitt Trigger inputs) – but with a Schmitt Trigger input inverter, the output should be oscillating between the Schmitt Trigger“offsetted” input levels – and I'm just seeing a fixed output, unless I've missed something, the only way that this simple RC circuit would not oscillate is if the Gates Schmitt Trigger input has failed – YES I 100% AGREE really odd, but its what I'm seeing... I've ordered replacement 74HC14's and I will see – if this is the case, then its a first for ME!!! mind you I've never used such a “Crude” but I guess normally effective RC circuit... When I was drawing this circuit section out - I was like whats going on here,??? then I understood that's its a "Funky" RC oscillator - or atleast its should be! - What do I know, I COULD BE WRONG!!!I 100% agree that under normal conditions 03 Error is related to Zeeman issues – but thisMIGHT OLYbe true under NORMAL conditions, HOWEVER:-1. The MCUNEVERconfigures the 6810 PIO which is used to interface to the PCM54 DAC nor selects the Analogue S/H Mux IC's on the output of this DAC.The Servo board design uses a single DAC PCM54 (There is a second DAC, a AD7524 which is an R2R Multiplying DAC that is used to set the Analogue Gain of the amplifier section processing the Cs Tube Output Signal (DAC Gain) before this “Amplified” signal is fed into the Mux'ed ADC section.The output of the single channel PCM54 is fed to a Analogue Mux IC (U44) which depending on the Servo board version feeds 3 or 4 S/H circuits (based around U47 and the low loss light blue Polypropylene film capacitors) – depending on board versions you can see these 3 or 4 of these PP Film Caps located around U47.Output A0 of the Analogue Mux IC U44 feeds the circuit around U46 (this circuit section is under the conformal coating to insure stable performance under varying environmental conditions), with the aid of the Analogue Mux IC U45 which the Servo board MCU selects to be either a LPF or 1st order Integrator depending on Cs Zeeman signal condition.This Mux IC is interfaced to the Servo MCU by a spare “Interrupt / I/O” pin on the 6810 PIO – as with the PCM54 DAC this is NEVER set to Integrator mode (which i believe it should be during Zeeman Signal search) – once the correct Zeeman signal is found the MCU should set to the Long term LPF mode... The Output of this selectable LPF / Integrator is used to control the 10MHz Master Oven oscillator VCXO pin. (I'm not 100% certain if LFP or Integrator Mode should be selected during initialization / Zeeman signal search mode, when time allows I will simulate this circuit to better understand).As there is no communication between the MCU / PIO nothing functional can happen with the Cs Tube section etc.2. The MCUnever writesto U29 which is an 8bit R2R Multiplying DAC used to set the Analogue Gain of the Cs Tube signal Input Amplifier(sets the Gain of the recovered Cs Tube Zeeman signal before its fed to the ADC stage). Its this R2R DAC “level” that is indicated by the “DAC Gain” window in the montor3 program – 256 being the highest Gain level (being an 8b DAC).3. The ADC isNEVER Readby the MCU –so the MCU can know NOTHING about board voltages, Clock Levels, Zeeman signal etc...4. The STEL NCO isNEVER configuredby the MCU to the ~ 12.6MHz andwithout this 12.6MHz signal nothing can function– I must stress the MCU makes NO attempt to configure the NCO, so its not an issue of a bad STEL as its never been correctly configured by the MCU.The ONLY action I see by the Servo Board MCU is to write to the 68B50 ASYNC UART with a ~1 second repeating “ERROR 03” - why the MCU should do this while its NEVER communicated with any other peripheral IC on the PCB to “know” the true status of the unit is puzzling – YES I understand that ERROR 03 is a “Zeeman Error” but its irrelevant asthe MCU has not attempted to correctly configure the Servo board peripherals for initial operation– no initialization of any of the Servo circuits / IC, even the NCO is not written to.Due to the apparant lack of initialization of any of the peripheral IC's on the servo board by the MCU, this points to a very early stage issue with the MCU:-1. Corrupt ROM2. Failed SRAM (MCU RAM)3. Failed “Communication” during peripheral IC initialization / configuration process such as the PIO, NCO, ADC etc. causing the MCU to loop, but why not display a relevant error message ?4. Failed MCU5. An odd corruption in Flash EEROM6. Something stuck / hung on an Address or Data line7. Address decoding error.... (an issue with peripheral / address decoding logic)Power and MCU clock are present and correct.Maybe a clue is in the fact that the Serial TX speed is set to 9600 Baud rather then the 2400 suggested in the user manual – maybe even the this is being incorrectly initialized... also the message “ERROR 03” which fits within a single 8 Byte word TX Buffer... but then maybe I'm over thinking this too much...I'm using a digital scope to monitor the peripheral devices chip select lines during power up – maybe I'm missing something so I will connect up a logic analyzer to try and find out at which stage the initialization progress / fails... but first I'll wait for the replacement SRAM – basics firstas probing with a Huntron Travker I do see a differtance with the A0 pin on the SRAM IC - otherwise the other Address lines on the SRAM IC all look the same.

author: bostonman
author_rank: Super Contributor
timestamp: July 10, 2025, 01:14:07 pm
content: You're way too far down the rabbit hole at this point and even I am confused.So far you have a questionable power supply, the B board in the power supply is questionable because it's not transmitting serial data, the STEL may be bad, you may have a bad ROM, bad microprocessor, bad 12.6MHz circuit, possibly the unit saw over voltage thus damaging chips/components, an error 3 that you're telling me isn't a Zeeman error (as reported in the manual) and you're guessing it really means memory error, bad individual data signals, corrupt FPGA, you're uncertain if the tube is any good, etc...Either the unit is extremely damaged, to the point it's beyond repair because it's been completely hacked, or you're making too many assumptions. Never in my time have I seen a unit that's had this many issues. I've even seen units that were dropped and banged that broke the mechanical structure and still had less issues.As I mentioned to you in PM a week or two ago, you need to provide pictures to see what you're working with and work at a basic level. Also, as I mentioned, you need to figure out what works, I know the twenty or thirty things that don't, but try figuring out what works. I've seen this issue with people who tried to work on these units, they spend more time looking at individual signals trying to figure out whether the overshoot on a square wave is causing issues and they think they are smarter than the unit.Why are you deviating from the manual? If the manual suggests 2400 baud, then set it to 2400. You're not transmitting a BluRay 4K movie, it's a string of data. When you start throwing anomalies into the equation such as changing baud rate based on the suggestion(s) of the manual, and you're getting odd results, then it makes it harder to determine the issue(s).

author: ITDH
author_rank: Contributor
timestamp: July 10, 2025, 02:42:12 pm
content: Quote from: bostonman on July 10, 2025, 01:14:07 pmI'm Well, Well, Well down a very deep Rabbit hole now indeed- but if a company does not release service manuals then how else can one repair?Quote from: bostonman on July 10, 2025, 01:14:07 pmSo far... again I've never worked on such a unit, so I'm a complete novice and I'm just working though things I can understand - for sure I'll be making incorrect assumptions, but I'm learning here by my own mistakes- as the internet is eternal – I hope that my escapades might help others – hopefully gaining some useful insight from my Rabbit hole diving and misadventuresAt the end of the day - I WILL get this unit working - only then will we see if the Cs Tube has any good life left in it!!!Quote from: bostonman on July 10, 2025, 01:14:07 pmI purchased this unit from a seller who had it buried in a corner to be used as spare parts unit after many a failed repair attempts - the Cs Tube was OK BEFORE the repair so its seem like a worthwhile risk... it now appears much damaged has been caused by an overvoltage of the 5V rail. To be fair the seller didn't want to sell me the unit - saying using his words “Too many Cooks in the Kitchen” = too many engineers having worked on the unit in the past...At a basic engineering level this is a “recognizable” design with ONLY the Cs Tube being a show stopper... the rest of the unit is easily understandable circuit blocks... this holds true for almost all designs at the end of the day...So long as the Cs tube is OK (and we have a good copy of the ROM code), then there is NOTHING in this design that cannot be repaired, replaced or even redesigned - even the STEL can be replicated in a small FPGA thesedays... it would take me a week at Max... I've already considred that as the DAC is operting at 45MHz, and we are generating a 12.6MHz Clock with LF modulation I'd even consider to Noise-Shaping the 12bit output to the DAC to improve the inband Dynamic range of this DDS generated "Clock" if I had to replicate the STEL in a small FPGA - again NOTHING show stopping here!!!Quote from: bostonman on July 10, 2025, 01:14:07 pmI've posted pictures here in the thread of the Servo board - from what I have seen there are no unique markings on my unit.... however I can post a pictures of my units the serial number...Indeed, it does now seem that I need to goto the basics - with so little apparent activity from the MCU its now wise to look at RAM / ROM and anything on the MCU Address / Data Bus that might be corrupting the initialization progress - I'm holding out hope its the SRAM, otherwise I'm going to have to go down a really deep rabbit hole with the logic analyzer...Quote from: bostonman on July 10, 2025, 01:14:07 pmI'm not deviating or changing anything - only that the reported ERROR 03 code is being transmitted over the serial port at 9600 baud - consequently I have to configure my Serial port to 9600 baud to be able to read these messages - hey I'm open to suggestions as what I can do in this situation- considering I CANNOT communicate to the Servo board MCU, but ONLY receive these repeating message!!! Monitor3 does not see my device - I can only see these messages using puTTY serial terminal.I guess my train of thought was that even the Serial port TX speed is incorrect – again pointing to a clue that the MCU appears unable to correctly initialize devices on its own interface bus...

author: bostonman
author_rank: Super Contributor
timestamp: July 11, 2025, 01:58:46 am
content: QuoteKeep me posted how you make out.Thanks for all the updates.

author: ITDH
author_rank: Contributor
timestamp: July 11, 2025, 02:48:27 am
content: I'm waiting upon replacement parts - I've removed all the Through-Hole DIL parts and have ordered Turned-pin sockets for them - then I can just use the "Parts Canon approach" and blindly swap parts if needed - hey this method at my expence seems to work for my local car service center!I've ordered replacment SRAM (from Turkey of all places) - its still not been shipped- the SRAM IC on my servo board failed when tested as a 6264 in my T48 Programmer / Chip tester... (there are differences between the address line arrangement between 6264 & the HM65764 / CY7C186) but I dont believe this matters.. (the Address line are just scrambled, but this should be OK if the Address ordering remains the same during both the Read and Write cycles).I've ordered replacment 74HC14 - unless I've made an error tracing out the board schematic and I believe I should see Oscillation on pins 10/11 of U14...I've also ordered some SMD ZIF to DIL sockets so that I can test each SMD logic IC on the servo PCB if all else fails...What would REALLY be helpful is a second Servo PCB - (there must be units with EOL Cs Tubes... this would really help me in debugging my board - I'm happy to purchase a unit or servo board if anyone has a one available).

author: edpalmer42
author_rank: Super Contributor
timestamp: July 11, 2025, 03:12:55 am
content: If you did have an overvoltage event, half the chips on the board could be fried. My guess is that the more complex chips would fail first.Since the processor is in a socket, you could move it to a breadboard and set up a minimal system that would blink an LED. That would establish that the CPU is at least somewhat alive. Used replacement processors are widely available for only a few dollars. You could even try buying one or more processors, but you'd still have the problem of confirming that the purchased chips are alive so ......Another possibility is to program another eprom with the firmware that I posted earlier. Step carefully here. I don't know if older firmware would cause a problem with your system.I would remove the STEL-1173 from the board for now. Until you can establish communications with the processor, nothing else matters. Removing that chip won't cause any issues because it looks like many of those chips fail and replacing them is all that's required to fix the unit.

author: ITDH
author_rank: Contributor
timestamp: July 11, 2025, 03:57:45 am
content: Yes, thats my plan moving forward - I've already removed all the DIL parts apart from the PCM54 DAC, atleast for now - waiting for some turned-pin DIL sockets and I'll take it from there.I'm really interested to see if my SRAM is indeed Bad - or its just that the T48 does not have the exact part number in its Database...Also if the 74HC14 is bad.. that would really be a bad sign!! I've already replaced U35 (74HC74) which was bad for certian (Q Output measured 40 ohms to ground even when powered off)...Next time I order from Mouser I might just order all the CMOS logic parts and as you say order some of the larger IC's from Ebay - espically the 6821 PIO ... I just have a bad feeling about this part...STEL already removed from its "New" PLCC socketI also now have a few untested spares...Waiting for the SRAM and DIL sockets first

author: ITDH
author_rank: Contributor
timestamp: July 21, 2025, 12:24:57 am
content: I'm still waiting on parts to arrive from China so I have little progress to report on my units repair.While waiting for the parts, I've partially drawn up the Servo boards digital section – this will aid me to further debug the board if the fault is not due to a bad SRAM or PIA IC.I've removed and tested most of the CMOS 74HS series logic around the Micro Processor section – all tested OK using a T48 – but I'll replace them preemptively with new parts considering I suspect the PCB substained overvoltage damaged when the PSU failed due to the leaking / open circuit filter Caps. (A Tant Cap on the -5V Regulator input was short circuit and a 74HC74 had a bad output ehich measured a fixed 40 ohms to Ground).In my earlier posts I suspected U3 - 74HC14 was bad as I didn't see oscillation on the WatchDogTimmer RC Oscillator circuit, but this was my error – the Oscillation of around 10Hz failed to trigger my Scope (Trigger was set to LF Reject - my Bad!!) - I don't normally measure such LF signalsanyway the RC Osc. circuit in the WDT is working OK which is a good sign... if a "Simple" logic Gate such as the 74HC14 had been damaged then this would be a very bad Oman...I've attached a partial schematic of the Servo board digital section that I've drawn up thus far – its not the most interesting Cs circuit section, but its what I currently need to hopefully facilitate the units repair.I've manually traced the circuit out – so expect errors and theSignal Annotations are my OWN– based on my understanding of the circuit operation– if anyone spots errors then please let me know and I'll make the relevant corrections...PCB version is:-SERNO 56219-ASY 08845-501 – this is the Servo PCB version with 5 Multiplexed DAC channels – with ROM Version 2.0

author: ITDH
author_rank: Contributor
timestamp: July 22, 2025, 09:30:39 pm
content: A more complete schematic of the Servo Board - SERNO 56219-ASY 08845-501I'll draw up the final Analogue sections when time allows completing the Servo PCB - hopefully it might be of some help to others in the future..Again I've manually traced the circuit out – so expect errors and theSignal Annotations are my OWN, unfortunately I've not found any offical schematics or sevice information for the unit.

author: bostonman
author_rank: Super Contributor
timestamp: July 23, 2025, 02:21:03 am
content: I'm curious, what are you using to measure the very low capacitors (i.e. 100nF)?Not sure I have a meter that is accurate enough for this and/or goes that low.

author: ITDH
author_rank: Contributor
timestamp: July 23, 2025, 02:31:29 am
content: Quote from: bostonman on July 23, 2025, 02:21:03 amI used a good old HP4275A for Cap. measurements - I'm guessing you meant the smaller values such as 10pF...

author: bostonman
author_rank: Super Contributor
timestamp: July 23, 2025, 02:34:38 am
content: QuoteIt was a test, you passed.

author: ITDH
author_rank: Contributor
timestamp: July 23, 2025, 02:41:55 am
content: Quote from: bostonman on July 23, 2025, 02:34:38 amI wish my school English classes where so easy - I got "unclassified" in English 3 times!!!

author: bostonman
author_rank: Super Contributor
timestamp: July 23, 2025, 02:51:46 am
content: I'll give you credit, you're doing a great job tracing all those circuits. A few years ago I worked on an Agilent 54831 scope and traced a few circuits.It wasn't easy and I used a steel wire brush to narrow down the area a connection went to, and then touched various points in that general area.If I were to guess, you're drawing the IC and then tracing those points whereas I didn't have the luxury of ICs and traced components through blind and (I believe) buried vias.

author: ITDH
author_rank: Contributor
timestamp: July 23, 2025, 03:12:30 am
content: Luckily no buried vias on the PCB - and its all fairly simple circuits, with just a few head scratching connections - such as the location of the 249Ohm resistor on Opamp U70's output. I really don't understand whats going on here – I double and triple checked my work... I trust its not a layout error. I can only think that the designers had transient issues with the Synchronous detector - but if true then its a "clunky" way to solve them.. but its all too easy to critique a design from the "Arm Chair" as it whereThe hardest board to trace out is the smaller PSU board – there's a lot going on there and also ALOT of hand modifications!I will draw up both PSU boards when time allows as this will help those whose boards have been physically damaged by Capacitor leakage... The larger PSU board is easy – its the smaller board that I'm not looking forward to.

author: bostonman
author_rank: Super Contributor
timestamp: July 23, 2025, 12:49:11 pm
content: You're correct, critiquing is easy, but lots of those circuits have reason for their particular designs due to various specifications the units needed to pass.Also, those circuits are designed to handle sub-assemblies that work differently including different oscillators, different tubes, etc... So you may see a component that should be installed and isn't, or vice versa; or a component value that is different than other units. Maybe a resistor that's piggy backed, etc.. You may think you'll understand a circuit based on the particular components, but it's very easily possible a sub-assembly has been changed without changing the correct components to accommodate so the unit won't work correctly.Also, as the tube aged, the oscillator aged, etc... components would change values to accommodate and keep the unit working.

author: ITDH
author_rank: Contributor
timestamp: July 23, 2025, 01:18:42 pm
content: Quote from: bostonman on July 23, 2025, 12:49:11 pmYes I 100% agree - I was also thinking this morning while making my tea - I wonder how many of my own designs have errors I don't know about - errors introduced during the PCB design stage where a schematic was incorrectly translated to the PCB...Quote from: bostonman on July 23, 2025, 12:49:11 pmYes, I noticed this in the VCXO circuit where option resistors can be populated on the PCB for Symmetrical or single rail VCXO control of the various OVEN Oscillators - also the "Matched" Cs Tube "header block" in the contorller PCB has spare postions - I'm guessing to allow a selection of older / newer Cs tube generations...My PSU contorller board has very heavy modifications - with many legs cut on Opamps - and the main feedback loop was changed during production to take the main feedback connection Pre LC filtering on the 5V rail by adding a long wire from the Main PSU PCB to the smaller controller PCB....Quote from: bostonman on July 23, 2025, 12:49:11 pmYes, that's good thing for the customer - something that you can only really get feedback and experance with once a larger number of units have been out in the field with a few years of operation - its VERY hard for the development team to see this with "few" R&D units built within the “short” time available during development and testing... Cs Clock are not easy with complex physics packages etc. This is really where the main IP is – much learning from the experience of PAIN.. sadly its a fact of life when you have so many variables and complex designs... Everything works perfectly in the lab - but it will be the units shipped to your most important customer - who of coarse also happens to be on the otherside of the world is where you start to get problems... LOL Life !!

author: bostonman
author_rank: Super Contributor
timestamp: July 23, 2025, 01:35:52 pm
content: That cable on the A-B power supply wasn't an upgrade, that was always there (until it went to SMT).Some components went obsolete, and replacements didn't work correctly, so other components had to change (i.e. piggy back or whatever).You may be able to trace the circuits, but trust me, you won't understand the reasoning for lots of stuff.

author: ITDH
author_rank: Contributor
timestamp: July 25, 2025, 01:36:24 pm
content: Finally some progress on my units repair !!My main suspects are the SRAM or the PIA - I removed the SRAM (HM3E-65764N-5) and tested using a T48 - but the closest SRAM part the T48 Database is the 6264 - which failed when tested:-Its my first time using the T48 to test SRAM - however as the Address line ordering is different between the HM3E-65764N-5 and 6264 I could not be certain of the validity of the failed T48 test results...Where ultimate SRAM Read / Write speed is not a concern, I understand the that the physical Address line arrangement does not matter so long as this same Address Line layout is used for both the Read and Write cycles.In fact, in my redrawn schematic of the 5045 Servo board you can see that the 65764N SRAM Address lines do not match the 6809 MCU Address lines (I presume that this was done to ease PCB routing for the more "conventional" Address Line sequence of the "parallel" connected ROM & EEPROM).I ordered replacement HM3E-65764N-5 from a vendor in Turkey and also from China as a backup – but none has arrived yet. Its bugging me that I'm no closer to repairing the unit, so I managed to find Narrow Packaged DIL28 part in Germany – HM3-65764N-5 (the same package style as used on older 386 / 486 Cache RAM) and they arrived todaySo the T48 can test HM3x-65764N-5 as 6264 SRAM andthis also means that my boards original SRAM is BAD!So this is the third damaged componenet and one PCB manufacturing error from factory (due to a physical PCB short – it would appear that the WDT circuit was never operational).I'm still waiting for the standard width DIL28 SRAM to arrive, but I'm glad I found a bad component – notably one that can explain the limited functionality of the MCU.As I have my suspicions that the PCB has been damaged by overvoltage as a result of the "failed" PSU repair – I have gone ahead and socketed the DIL IC's and will replace all the SMD CMOS logic on the board (I should also replace the Tantalum Caps as Tant Caps. are very sensitive to overvoltage)...I've de-populated the PCB - ready for rebuilding one the parts arrive.Once I manage to get my unit operational – andIF my Cs Tube is still good, then I plan to modify the design for lowest close in Phase Noise performance and cleanest spectral outputlooking forward to the challenge and learning along the way

author: bostonman
author_rank: Super Contributor
timestamp: July 25, 2025, 01:51:31 pm
content: QuoteWhy not test this first?

author: ITDH
author_rank: Contributor
timestamp: July 25, 2025, 02:27:49 pm
content: What do I need to test the Cs tube? - I'm guessing a ~9GHz+ Spectrum Analyzer? I only have a 4GHz SA here, I have 26GHz HP MMS system in storage however its not easy to get too and its also not been used for a few years...It be really great if I could confirm the Cs tube healthI've seen a thread somewhere about testing Cs Tubes but it required a whole host of HV PSU's etc. it did not look easy - so I thought it just be easier to get the Servo board going...I have a couple of Cs tubes I recently purchased - but I'm not sure how easy it is to install these without Factory service info...

author: bostonman
author_rank: Super Contributor
timestamp: July 26, 2025, 06:04:35 pm
content: It comes down to experience. You wouldn’t get a definite answer, but with some creativity to power the tube,, you can get an idea if it’s a junk tube.If I had pictures of the entire unit and the Servo Board didn’t tinkered with, I may have more insight. Also, you can repair all those assemblies. You may get the unit to work, but it will be far off frequency without proper tuning.

author: edpalmer42
author_rank: Super Contributor
timestamp: July 26, 2025, 07:30:27 pm
content: Here's a page that shows some Cs tube bench tests:http://www.ke5fx.com/cs.htm.I was able to test the tube in my 4065A (5045 module) as follows - note that the power supplies were all working so I didn't have to deal with anything there. Obviously, the ion pump must have already pumped the tube down to a good level. Mine started at over 100 ua and came down to 0 ua.1. Replace the internal oscillator with a fixed 10 MHz source - I used an Efratom FRT Rb. This prevented the processor from trying to tune it.2. Replace the 12.63x MHz synthesizer with a programmable generator referenced to the 10 MHz fixed source. The accuracy of this source will determine how close the resulting peak is to 9.192xxx GHz, but the peak will obviously be at the correct frequency, even if your measurements & calculations say otherwise. In my case, I ended up at about 9.192 631 780 GHz or about 10 Hz off.3. Replace the output of the Cs tube with a >1Gohm impedance DMM in parallel with a 100 Mohm resistor.4. Write a program to step the programmable generator in 1 or 10 Hz steps around the required 12.63xxxx Mhz range and measure the DC voltage from the tube after each frequency step. Convert the voltage to current through the 100 Mohm load.5. Graph the current vs. frequency at the resonance frequency of 9.192xxx GHz.Although I replaced the synthesizer and the OCXO, the processor was still trying to lock the tube so there may have been some uncontrolled parameters that distorted the results. C-field is one obvious factor. Regardless, I've attached the graph that came from my tube. The manual for the HP 5061A gives a method to calculate the 'health' of the tube based on this response. I doubt if it actually applies to the FTS tube, but it's all we've got. The HP tube is spec'ed at 200 na output. My tube only has an 11 na output. It may be on its last legs or that could be normal.

author: ITDH
author_rank: Contributor
timestamp: July 26, 2025, 08:27:23 pm
content: @edpalmer42Thank you very much for the information - was this your test bench in the link? but I'm guessing your not John Miles? John's a great guy and he helped me getting my E5500 PN system going... I've since purchased his TimePod PN system which is now being sold by MicroChip of all people!!WRT to testing the tube using as you suggested - this will not work for me at the moment as the Cs Tube power supplies need to be enabled by the MCU - these are enabled once the OCXO Oven has warmed up and the oven current requirements have reduced - from what I have deduced from the available information this is to limit the 5045 modules peak power requirements - so the Cs supplies should be enabled about 5-10 minutes after initial power-on once the oven current has reduced...I'm guessing the 10Hz Cs resonance offset you measured was due to the MCU being unable to control the C-Field servo loop - the 5045 Datasheet mentions "C-Field locked to Zeeman resonance peak", which obviously in your test setup it was unable to doI need to complete the Servo board schematic - then I'll draw up the smaller PSU B board which has the C-Field circuitry - then we can get a clearer understanding of the whole units functionality – there are a 3 Analogue control signals from the DAC on the Servo board to the PSU B board (a couple are VCXO and RF Level) so I'm going to make a best guess and say the remaining must be for the C-Field Control Loop – once I draw up the circuit things will become clearer

author: edpalmer42
author_rank: Super Contributor
timestamp: July 26, 2025, 09:23:06 pm
content: Quote from: ITDH on July 26, 2025, 08:27:23 pmNo, KE5FX is another user here. He's way ahead of me on this stuff. He's the author of Timelab which has become the goto software for measuring oscillators within the amateur, and maybe professional, Time-Nut community.QuoteSure, but since you know what's supposed to happen and when, you can manually enable the appropriate power supplies at the appropriate times, whether you used internal or external supplies. That's what KE5FX did. For the high voltage supplies, you could manually power and enable the power blocks that are in the 5045. It would be a shame to spend all this time and effort reverse engineering and repairing the servo board only to find that the tube was dead. Remember that an exhausted Cs supply is the most likely failure mode for a Cs standard. Although it's also true that a dead power supply, or in our case a dead STEL-1173, might have prevented the Cs supply from being used up. YMMVQuoteYes, I mentioned that just to document the frequency error that will likely appear in your data. C-field control isn't necessary to test the tube.By the way, if it wasn't obvious, both the programmable generator and the DMM need to be remotely controllable to set the frequency, measure the response, and record the data under computer control. Only a masochist would try to do this manually, particularly with 1 Hz steps. I used 10 Hz steps and it still took 400 steps. In hindsight, I wish I'd used 1 Hz steps and gone over a wider RF range to capture the adjacent response sets.

author: ITDH
author_rank: Contributor
timestamp: July 29, 2025, 01:13:43 am
content: "Full" Working Schematic of the Servo board for the FTS / Datum 4040A/RS with 5045 Cesium Module.Basically complete - minus PSU / local decoupling Capacitors... but it should still be helpful for unit repairs etc.Signal Annotations are my ownbased on my understanding of the circuit operation - I've "Manually" redrawn these schematics from the PCB so expect errors...Once I have time I'll draw up the PSU A & B boards...

author: bostonman
author_rank: Super Contributor
timestamp: July 29, 2025, 02:08:27 am
content: J6 is the CBT signal output, not the EM.Also, I wouldn't use 12.6317743133 MHz as the frequency because that changes.

author: KE5FX
author_rank: Super Contributor
timestamp: July 29, 2025, 03:33:42 am
content: Quote from: ITDH on July 26, 2025, 08:27:23 pmThanks!I don't see any reason to think your tube's not good. It's good news when you know that your Cs standard was taken out of service for a failure other than tube aging, because it was presumably working before the unrelated failure occurred. I would keep doing what you're doing, focusing on getting the rest of the hardware up and running.The bench test setup I used with the HP 5062C tube was built from a complicated mess of power supplies and other equipment. I don't think it's worth trying to duplicate it with your tube, unless you just want to see it work from first principles. One false move with a power supply could potentially destroy the tube. But if you did want to try testing it, see if the manual talks about an "LF coil" or low-frequency coil that can be driven by an audio oscillator at half the Zeeman frequency to stimulate beam current without microwave input. (Assuming thereissome sort of manual, and it sounds like there isn't.)The Datum 4060A manual calls it a "flop coil," connected to a gray wire at pin 2 at the oven end of the beam tube. I've actually never tried that test procedure myself but the HP 5061A manual talks about it.

author: ITDH
author_rank: Contributor
timestamp: July 29, 2025, 04:12:36 pm
content: @KE5FXThank you for post and the encouragement to keep going- I'm semi-retired now and have limited resources here in my "home lab" due to space limitations so things take a little longer then I'd like...The LF test to stimulate beam current without microwave input you mentioned is VERY interesting - I searched for some information in the FST_4060 service manual posted earlier in this thread - but it looks like the relevant section is missing with just the start of the paragraph section to tease me!! Would you happen to know if there is a more complete section anywhere? in the meantime I'll read the HP5061 manual.For my applications I require "State of the Art" Close-in Phase Noise - say from 0.1Hz to 50KHz, within this B/W the Oven OCXO and any distribution Amps etc. between the OCXO and output connecter are basically responsible for this PN region - but I'm wondering what effect the LF noise of the 12.6MHz NCO, subsequent frequency multiplication blocks and even the TIA Stage recovering the Cs Signal contribute to the Close-in PN of the system?I ask this as I understand that the LPN performance options seem to operate the Cs Tubes at higher power and hence shortening there lifespan - could one achieve improved PN with a standard CBT but with lower noise servo electronics?Considering the very high multiplication factor of the 12.6Mhz signal - I would have thought that the intrinsic PN of this signal would be a critical factor?Its not hard these days using modern DDS techniques to generate a higher "base" frequency (which would require less frequency multiplication and subsequently less PN multiplication) with a greater dynamic range then the 12bit NCC of the 5054?So I'm toying with the idea to give it a try just for fun - maybe also using a Lock-in amplifier with a very narrow B/W to recover more of the signal buried within the Noise floor - I have a SRS 850 DSP lock-in amplifier in storage just waiting for such a projectI'd just like to better understand the ultimate limitations of CBT's... From what I can tell, the FTS4040 is really designed for Telco use where PN below 12KHz or Spectral purity is not important, but there's nothing to stop one to build upon the existing hardware just to see how far it can be pushedJust a quick thanks again for your Timepod designs - its "Game Changing" for high performance close-in PN measurements not to require a second identical clock to the Measurement clock - this is what made using the Agilent E5500 so troublesome for me.I purchased a 53100A back in 2022 (during Covid) but it took over a year to arrive - sadly it arrived after the project was completed so its sitting unused in its box - as yet to be powered up (I had to use my E5500 system)... if it be OK in the future to ask you some questions to getting the best performance for measuring Close-in PN on a 100MHz clock design I'll be working on?Would a couple of SRS PRS10 be OK as the Reference Clocks? (They have quite good close-in PN) - should I Lock the PRS10's together?

author: KE5FX
author_rank: Super Contributor
timestamp: July 29, 2025, 06:04:19 pm
content: Quote from: ITDH on July 29, 2025, 04:12:36 pmI'm not familiar with the Datum standards or their manuals, but I suspect the HP manual is the best way forward here. The tubes are similar enough to be interchangeable given the appropriate wire harnesses. HP basically says "Feed it a 1-volt signal at Z/2 Hz and watch the beam current," and little beyond that.QuoteThe synthesis and signal-recovery chain does make a difference. HP spent a lot of time and money improving that part of the 5071A design vis-a-vis the 5061A/B, and they ended up doing about 10 dB better in the 0.1 Hz - 1 Hz range. But it will always be a second-order effect compared to the tube itself.CBTs have terrible S/N ratios even when brand new (note edpalmer's reference to beam currents in the nanoamp range above.) So the OCXO must be disciplined with a long time constant, typically from ~1 second to over 1 minute depending on the expected operating conditions. Even so, running any Cs standard in unlocked mode will always give you better PN at offsets below ~10 Hz. I don't know exactly what behavior to expect from a Datum standard, so that's worth checking yourself to see where the limits ultimately lie.QuoteGoing back to the HP 5071A example, the differences between a 5071A and 5061B are noticeable in that range, and the tubes themselves are known to be very similar.QuoteYes, and that's part of what Karlquist and others at HP were looking to improve when they redesigned the synthesizer in the 5071A. But that really was a clean-sheet-of-paper design effort (as were the Datum designs of course), and I'm not sure what factors ultimately proved to make the biggest difference.QuoteCorrect, which is what HP did, but I don't think they would call it "not hard."The reality is that an SRD multiplier is not terrible, if fed with a clean drive signal. Whether the 5071A's advantage came from improvements in the microwave multiplier chain or improvements in the HF synthesizer, I can't say. Rick Karlquist has written a fair bit about it on the time-nuts list, in addition to the contemporary papers the team published. It'd be a good idea to go back through that material before basing any new work on any critical assumptions that might not be justified.QuoteI've done some tentative experiments along those lines with a 5065A Rb standard. Results are promising -- the synthesis chain is fairly similar to the Cs standards and (again) not that terrible, but its close-in noise can be beaten with modern hardware and it does appear to help. Much of the improvement that I saw was likely due to the use of a longer loop time constant than stock, though. It will take some more R&D time to learn what really matters and what doesn't.QuoteAbsolutely! Either here (although please start a new thread) or in email is fine, happy to help.QuoteIf you are measuring at 100 MHz, then no, those are probably not ideal due to the 20*log10(N) penalty. It's usually best to use VHF references to measure VHF sources, because otherwise you may have to wait an unreasonably long time for the results to settle.Take a look at the section on the internal reference option in thenewer editions of the manual(page 221 in the 1.09 version). If available, good external references are just as effective as the internal references, but the same performance considerations apply. When you are measuring the close-in noise of VHF oscillators that are expected to outperform your reference(s), it's best if you can use a pair of references with better close-in noise than VHF OCXOs typically provide by themselves. Otherwise, again, you may have to wait longer than necessary.If you do lock them together, the loop bandwidth should be much lower, ideally 10x or more, than the lowest PN offset frequencies that you care about measuring.

author: ITDH
author_rank: Contributor
timestamp: July 29, 2025, 10:10:58 pm
content: Quote from: bostonman on July 29, 2025, 02:08:27 amI wasn't sure how to call this input from the CBT - from my understanding the the Electron Multiplier is the ion detector in the CBT, so the CBT output signal is from the Electron Multiplier - which is why I labeled it as such.I should really have read other Cesium clock service manuals so I would have picked up the "standard" lexicon describing the various signalsQuote from: bostonman on July 29, 2025, 02:08:27 amTrue, however I did this deliberately so I wouldn't need to keep looking up the "Idealized" Frequency - I'll add a note to this effect in the next schematic release

author: bostonman
author_rank: Super Contributor
timestamp: July 29, 2025, 10:58:47 pm
content: I may be wrong, but the 12.6MHz connector label is incorrect too, however, since you're looking at the Servo Board, maybe I just remember it wrong.As stated, the 5071A tube and the 4040A/RS tube are similar in that the physics are similar. After all, not many ways exist to excite atoms to get a signal out of a tube.If it hasn't been stated already, the 5071A was purchased by Symmetricom approx. 2004 and the CA building moved all the product to MA around 2008. Unless something has changed, both models were kept as is meaning the electronics from one wasn't implemented into the other; and vice versa.I've offered advice, and can tell you're following your own path such as tracing the boards, etc... but believe me, before you get into replacing components to improve phase noise or anything else, get the unit working/locked.Time and time again, many employees who were new hires thought they could test/repair these units their own way. I can tell you this much: none of them lasted in the company or they worked on Rb products instead. Many reasons exist for the circuit layout and/or reworks.It's possible you can add/remove something to improve a spec, I won't disagree with this, but the designs were made to meet certain specifications. Maybe you can improve phase noise by implementing a (I'm exaggerating for the purposes of discussion) $100 component whereas at the time, the spec was adequate for the product, so why add $100 to the cost of the unit? In your case, maybe it's worth the $100.

author: ITDH
author_rank: Contributor
timestamp: July 30, 2025, 12:14:46 am
content: @ KE5FX,Thank you John for the very detailed reply - much for me to ponderIf there where a company who are RF experts then its was the "Old" HP / Agilent guys... I'm not keen on there new Keysight designs however... so I really need to get my hands on a HP5071A, I just so happen to have a replacement (FTS branded) CBT tube for the HP5071 - and from my understanding the CBT are "user replaceable" as the Tube "characteristics" are stored on a EEPROM contained within the Cable harness D-type connectors."A New Technique for the Characterization of Cesium Beam Tube Performance"Attached is a paper I just stubbled across that goes into some detail concerning the CBT SNR. Not only is the signal current level very low, but it would also suggest that CBT are inherently very noisy (although its still not clear to me the source's of this noise - eg. how much of it is due to the PN of the uW RF signal source etc.)Would you happen to know the "Typical" Output Impedance of the FTS CBT tubes?

author: bostonman
author_rank: Super Contributor
timestamp: July 30, 2025, 12:52:39 am
content: QuoteI'm uncertain what type of FTS branded CBT you have, but....... I don't believe it's easy to swap tubes. The 5071A CBT sends additional information that the electronics/micro needs to see in order to actually get the 5071A to recognize it as a legit 5071A tube.In the older days Datum was able to swap their tubes into 5061 units, but then HP got smart and implemented some stuff into the 5071A firmware. Whether someone can hack it to get an FTS tube into a 5071A is a different story.

author: KE5FX
author_rank: Super Contributor
timestamp: July 30, 2025, 01:28:51 am
content: Exactly, the EEPROM's job is to make it impossible to clone the 5071A's beam tube.It's easy enough to copy the EEPROM, of course, but there's a catch: in addition to the beam tube parameters, the EEPROM contains a cheesy poem written by Jack Kusters or Len Cutler if I recall the lore correctly. I won't quote it here but anyone who can read a 24LC16 can find it. The firmware checks for the poem and refuses to boot if it's not there. So anyone selling a bogus beam tube is also committing a copyright violation, which makes it easier to shut them down in court.Of course at this point everybody who could build a CBT is owned by Microchip anyway, so any measures taken to deter Datum back in the day are completely moot. But if the Chinese get any bright ideas about selling 5071A replacement tubes, they'll be entering a world of pain.Quote from: ITDH on July 30, 2025, 12:14:46 amThe electron multiplier acts as a current source with a very low compliance voltage, so it doesn't really have a well-defined output impedance. It sends out a certain number of electrons per second. A DMM will read a voltage corresponding to the current times its own input impedance. Unless the input impedance is more or less infinite, at which point it reads the maximum compliance voltage.This type of device is more often encountered in the form of a photomultiplier tube, which traditionally drives a transimpedance amp with zero-ohm input impedance.

author: bostonman
author_rank: Super Contributor
timestamp: July 30, 2025, 01:42:19 am
content: QuoteGlad you typed that because I was reluctant to post it.

author: KE5FX
author_rank: Super Contributor
timestamp: July 30, 2025, 01:44:52 am
content: Spoiler:Ash tube durbatulûk, ash tube gimbatul, ash tube thrakatulûk, agh burzum-ishi krimpatul

author: edpalmer42
author_rank: Super Contributor
timestamp: July 30, 2025, 02:26:37 am
content: Much of the performance of this unit is determined by the firmware. Can you gain significant improvements in phase noise or any other parameter without reverse-engineering that? I would think that the 'frequency-hopping' that this unit does would really complicate the process.

author: bostonman
author_rank: Super Contributor
timestamp: July 30, 2025, 03:19:38 am
content: The frequency hoping is what keeps the unit locked and on frequency.As with many other things, it's a trade off. As an example, you can change the loop time constant, but then your offset is affected.Personally, I wouldn't mess with the firmware in hopes of improving anything.

author: edpalmer42
author_rank: Super Contributor
timestamp: July 30, 2025, 07:58:51 pm
content: Exactly. The hopping is used for locking, tracking, testing, and measuring. I counted a total of 24 discrete frequencies that the processor commands the STEL-1173 to jump to for all these functions. The jumps happen continuously as long as the unit is in operation. It's far from a simple analog or digital PLL.The RF signal to the tube is created by 10 MHz x 2 x 9 x 51 = 9180 MHz. Then the 12.63x MHz STEL-1173 is added to that to get to 9.192x GHz resonant frequency. So you might be able to clean up the basic multiplier chain, but the question is whether that would have a significant effect on the unit's performance - given that the processor is still jumping the 12.63x MHz signal all over the place.

author: ITDH
author_rank: Contributor
timestamp: July 30, 2025, 09:48:14 pm
content: Quote from: bostonman on July 30, 2025, 12:52:39 amI believe the FTS tube is an "official" replacement tube as it also comes with the mounting hardware to change the round drum HP style CBT tube to the FTS rectangle type tube - also I would expect that the EEPROM is already included in the D-type connector housing.The CBT Tube is in storage - but when I get the chance I'll grab it and take some pics and also confirm if the EEPROM is present - and if it is I'll make a copy...

author: bostonman
author_rank: Super Contributor
timestamp: July 30, 2025, 09:51:35 pm
content: Sure the tube isn't for a 5061?Maybe the company decided to make FTS tubes for the 5071, but doubt it. Why would they when they own the 5071?

author: ITDH
author_rank: Contributor
timestamp: July 30, 2025, 09:53:54 pm
content: Quote from: bostonman on July 30, 2025, 09:51:35 pmIndeed let me confirm that when I next have the Tube in hand - I'll post some pics...

author: ITDH
author_rank: Contributor
timestamp: July 30, 2025, 10:11:06 pm
content: Quote from: KE5FX on July 30, 2025, 01:28:51 amThe reason I asked about the CBT output impedance is so that I can better understand the Gain of theTransImpedanceAmp (TIA) or what I just call an I/V converter. The Gain of the TIA is determined by the CBT output source impedance - as you say the input impedance of the TIA is a Virtual Earth (Due to the Opamps feedback is practically Zero ohms) - at least within the Opamp's gain B/W.

author: bostonman
author_rank: Super Contributor
timestamp: July 30, 2025, 10:18:16 pm
content: On a new/good tube, the output current should be around 50nA. Update: assuming all tube supplies are optimal/working and the 9.192GHz is good.You can measure the output of the transimpedance amplifier to get the voltage. The 50nA is a good peak, but the unit can still lock in the pA range; it depends on the S/N of the tube too.The tube can have 50nA, but many other factors will cause high background noise causing the unit to not lock.

author: ITDH
author_rank: Contributor
timestamp: July 30, 2025, 10:33:24 pm
content: Quote from: edpalmer42 on July 30, 2025, 02:26:37 amMuch of the Frequency hoping products should be filtered by the VCXO Loop - once my unit is functional I have modulation analyzer on hand and I can post FFTs of the modulation spectrum.WRT close-in Phase noise and spectral purity of the Output clock, I can see some fundamental design limitations - this isNOTto criticize the design which I believe is very much targeted to the Telco "GPS backup" market sector - Telco's DON'T require ULN or clean spectral output - I'm guessing this is an area where the HP5071 would excel.I expect to see unwanted spurious PN components as a result of the CBT modulation process on the clock output - but I believe that these are "unwanted" second order coupling effects that can be resolved - but I'm making these assertions just based on my experience while looking at the units design. Once I get the unit operational I'm make the PN measurement's and then see if I'm correctand then I can have some fun playing and see how far it can be improved.Getting the unit operational first - then making the measurements are my first steps... lets see

author: edpalmer42
author_rank: Super Contributor
timestamp: July 30, 2025, 11:13:56 pm
content: Quote from: ITDH on July 30, 2025, 10:11:06 pmMy first attempt to measure my tube's response was to measure the output voltage across a 10M resistance. The peak voltage was 0V77 for an output current of 77 na. My second attempt was across a 100M resistance with a value of 1V17 for an output current of 11.7na. Assuming a constant output impedance and compliance voltage, this calculates to an output impedance of ~6.1 Mohms and a compliance voltage of ~1V24.So, now I'm not sure whether my tube is really good (77 na) or adequate (11.7 na). Whatever.

author: KE5FX
author_rank: Super Contributor
timestamp: July 30, 2025, 11:56:11 pm
content: Quote from: edpalmer42 on July 30, 2025, 11:13:56 pmIt's definitely meant to work into a low effective impedance (TIA with 3 to 10 megs in the feedback loop, built explicitly with an opamp in the 5062C but with a chain of 3 bipolars in the 5061A/B.) So you might get more consistent results with 1M resistor compared to 10M. I don't think you can infer anything based on 100M.77 nA is a lot compared to the ~0.5 nA that I saw I saw with the 5062C tube. I'd say it's in great shape as long as it's not too noisy.

author: KE5FX
author_rank: Super Contributor
timestamp: July 31, 2025, 12:13:58 am
content: Quote from: ITDH on July 30, 2025, 10:33:24 pmAs good as it is, even the 5071A is noisy compared to a good OCXO by itself. We actually use one for production test and calibration of the 53100As with the internal reference option. It was necessary to build an external cleanup PLL for it, just because the 5071A is nowhere near clean enough to serve as a reference for our ADEV tests in the t=1s to t=10s range.People use Cs clocks when they need good long-term performance (or in our case a traceable primary standard), almost never for phase noise.

author: ITDH
author_rank: Contributor
timestamp: July 31, 2025, 12:28:28 am
content: Quote from: KE5FX on July 31, 2025, 12:13:58 amI'm really impressed - I've never had much luck achieving LF ULPN using PLL loops - at least using analogue PLL's - hats off to you as I KNOW how hard this is to achieve!!

author: bostonman
author_rank: Super Contributor
timestamp: July 31, 2025, 01:14:00 am
content: QuoteThat's quite high. Are you sure the tube isn't running hot such as 125 degrees C?

author: edpalmer42
author_rank: Super Contributor
timestamp: July 31, 2025, 01:49:07 am
content: Quote from: bostonman on July 31, 2025, 01:14:00 amNo, it looks like the oven temp is 97C - see attached picture. Remember that my results were in a manual test with a random 10Mohm load. I don't know what the load should be. The history of my unit is unknown so it's possible someone messed with it.

author: bostonman
author_rank: Super Contributor
timestamp: July 31, 2025, 02:05:35 am
content: The correct way to measure it would be at the output of the transimpedance which has a 1M across the output and input with some smaller resistors/poteniometer (the pot is to adjust the gain).If you haven't and care to, check/confirm the oven temperature. You should see a blue and green wire if I remember correctly. Without getting into two-decades of what you may or may not possibly measure with the connector connected, it's easier to get the tube up to temp, disconnect power, disconnect the tube connector (15-pin?) from power supply, and measure the green and blue wires to ground.One should be 10x more than the other, but may not be.You should see one measure the 92ohms as the sticker shows and the other approx. 920ohms; or you may see 92 and 92, or even maybe 920 and 920 (I don't believe this is possible, but I don't exactly remember).Also, if I'm reading the tube s/n correctly and remember correctly, that tube was built in 2000.

author: ITDH
author_rank: Contributor
timestamp: August 01, 2025, 12:59:51 am
content: Quote from: edpalmer42 on July 30, 2025, 07:58:51 pmSo thinking in the bath (the only time I have time to think out of the lab) - I just could not get my head around why the designers would need 24 discrete Frequency's to achieve lock - this just does not make sense to me... I just cannot see it.... why, what am I missing?... (I could very WELL be wrong here).Then it got me thinking, are you SURE you captured 24x 48bits unique (6 Byte) words?The STEL-1173 input register requires 48bits per "Frequency hop" - this is transmitted as 6x 8bits (6 bytes) for a single Frequency "word / hop" - so I'm wondering did you see just 4 discrete Frequency's (4x6 = 24 "unique " 8bit words) - this would make much more sense to me...

author: ITDH
author_rank: Contributor
timestamp: August 01, 2025, 01:15:42 am
content: Quote from: bostonman on July 31, 2025, 02:05:35 amSo do I understand correctly that the indicated CBT operating temperature, as indicated on the Tube label (97DegC) is when the CBT Thermistor measurer's the indicated resistance (92 ohms) as indicated on edpalmer42's tube?

author: bostonman
author_rank: Super Contributor
timestamp: August 01, 2025, 01:38:18 am
content: QuoteI'm quoting myself above.I might be wrong, but believe it's less frequencies and not twenty-four. Also, the reason I quoted myself above is: to reiterate these are not units that anyone can turn a few pots to repair. Many people don't understand the design and criticize the circuits for being over designed or think they could design the circuit(s) better.Trust me on this..... I've heard it all over the years. You can change components, upgrade components, etc... and, as I previous said, maybe you will improve the unit because MAYBE it was designed to meet a set of lower specifications adequate for the customers. For the most part, those units are solid as is. Changing one thing WILL most likely affect something else. You want better stability, then sacrifice phase noise. You want better phase noise, then your offset will be worse.There are reasons for the frequency hoping and it comes down to the physics of the CBTs and phase locked frequency units. While I'm no longer obligated to keep the inner workings to myself, I'm still loyal on a personal level to only discussing what is public knowledge; not that I really know much anyway.Believe me, you're not the first person who has contacted me denying certain aspects of the unit and thinking they can achieve better performance. I had a guy spend over a week exchanging personal emails with me insisting his much older model unit could achieve offset specifications far greater than the newer/modern units. Each time he'd tweak something, he'd get great offset for about an hour and then it would drop. He'd send an email still determined that tweaking potiometers will achieve performance equal to a 5071A.As I said above, I've heard it all over the years. From new hires working on these units to strangers contacting me.

author: bostonman
author_rank: Super Contributor
timestamp: August 01, 2025, 01:39:55 am
content: QuoteYes.Remember though, it may be 97 (in your case) and 97, or 97 and 970, or maybe 970 and 970 (but I think this is unlikely). Update: give or take a few ohms. It may be 95 and 980.... don't be concerned over a few ohms. Also, the colder the longer your tube will last, but lower performance. Hotter (higher thermistor value), better performance, but less life.Also, don't ask why the different combination of thermistor values, just take it for what it's worth.

author: edpalmer42
author_rank: Super Contributor
timestamp: August 01, 2025, 01:47:41 am
content: Quote from: ITDH on August 01, 2025, 12:59:51 amYou're giving me too much credit. I didn't capture anything. The process is described in the 4065C manual. Only a few of the frequencies are used for locking. Others are used for C-field measurements / adjustments, others measure signal peak vs. valley, others check to make sure that the lock is on the correct set of peaks, etc. It's no wonder that the STEL-1173 dies - they work the poor thing to death.

author: bostonman
author_rank: Super Contributor
timestamp: August 01, 2025, 02:24:45 am
content: QuoteWho reads a manual?It's been so long since I glanced at the manual that I don't remember what is listed. Usually I learn better by talking directly to brilliant people, so lots of my knowledge came from drawings on paper towels during lunch.

author: edpalmer42
author_rank: Super Contributor
timestamp: August 01, 2025, 02:33:10 am
content: Quote from: bostonman on August 01, 2025, 01:38:18 amI didn't believe it either but .....Fr = Ramsey (main) peak frequencyFz = Zeeman peak frequencyFr +- 5 KHz - Initial Ramsey frequency lockFr +- unstated, but much less than 5 KHz - fine Ramsey frequency lock11 distinct frequencies - (values unstated) to measure / adjust- C - field- Ramsey peak to background- Zeeman peak to background- Central peak symmetry- Clock resonance pedestal symmetry (whatever that is!)- Microwave power levelFz +- 7 KHz - initial Zeeman frequency lockFz +- 350 Hz - fine Zeeman frequency lockFr +- 386 Hz - test to ensure that you're actually locked to the Ramsey peakSo, 2 + 2 +11 + 2 + 2 + 2 = 21My mistake. I double-counted the Ramsey and Zeeman peak / background ratio frequencies. They compare the Ramsey peak to the background level and the Zeeman peak to the same background level . Those three frequencies were included among the '11 distinct frequencies'.

author: ITDH
author_rank: Contributor
timestamp: August 01, 2025, 02:56:05 am
content: Quote from: edpalmer42 on August 01, 2025, 01:47:41 amWAIT - WHATthere is a Manual?I had no idea- I've just downloaded it and have only briefly skimmed though it - however its a GOLD mine of information, explaining SO much!!!If I had known earlier it would have made my job of annotating the PCB schematic SO much easierThank you for pointing it out to me - I'm a very happy Bunny!I'll update the schematics with clearer annotations

author: bostonman
author_rank: Super Contributor
timestamp: August 01, 2025, 03:03:08 am
content: Be aware, while I haven't read it or proof read it, at some point manuals were combined with pages from other manuals.One quick example is page A-17 is a screen capture from really old monitoring software. Still equally educational, but you may find errors that point to areas that aren't in the manual or wrong references.You're lucky to have found that because as time went on, the manuals shrunk.

author: edpalmer42
author_rank: Super Contributor
timestamp: August 01, 2025, 06:16:57 pm
content: Quote from: ITDH on August 01, 2025, 02:56:05 amIn a situation like this, I make a point of spending days sniffing around online to find every shred of information I can - every document, every mention of the product (or related products). I look here on eevblog and of course, for Time-Nuts stuff I check the archive of the Time-Nuts mailing list. Just asking for help isn't enough. You have to do the digging to find the gems. Weeks later, I do it again to see if I can stumble across anything I didn't find the first time. When I run into broken links, I get on a 'first name' basis with the Wayback Machine.In this case, I downloaded the manuals of every FTS/Datum Cs standard I could find. There's a family resemblance between them so lots of the info is transferable. I found a manual for the CsIII that describes some of the parameters that are poorly covered elsewhere. The 4060 is a totally different beast from ours, but the service manual has schematics! Interesting!

author: ITDH
author_rank: Contributor
timestamp: August 01, 2025, 07:40:40 pm
content: Your making me feel oldThis new fangled "Internet" - I just took it as fact that there was little to no information on the 5045 Module apart from what was published in the marketing and sales material...The user's manual is very well written - obviously from a time when engineer's where still allowed "In the Loop" - I wish I was aware of the manual before redrawing the schematic as it would have eased with the task of annotating the signal lines... but at the end of the day it made me smile as it confirms my understanding of the unit's operation..When you said that there where 24 different frequency's I erroneously interpreted this as meaning a continuous "Multitone" Spread Spectrum type signal - but in reality "Frames" are periodically stolen on a ~650mS basis to squeeze in House keeping / System performance check "frequency hops" for up to a couple of Frames (each frame is 17.92mS wide - so the Frame cycle rate is 55.8036Hz) - The repetition rate of 55.8036 Hz is filtered out by the longer time constant VCOCXO PLL loop (Apparently 5 seconds is the "default" loop filter TC setting).I'm Looking forward to getting my unit operational (I wonder what the DAC Gain setting will be - as this is indicative of my units CBT health) and then being able to make some measurements to confirm "our" understanding of the units operation.Yesterday, I finally had time to order the 74HC series logic from Mouser - the shipment should arrive Monday or Tuesday - however here in Monaco, France handles the customs processing which is never good and is much worst at this time of the year as everyone is on Holidays

author: bostonman
author_rank: Super Contributor
timestamp: August 03, 2025, 01:20:10 pm
content: QuoteYou'll find most manuals have the same information, and, as previously stated, probably errors in newer ones due to combining pages from old to new. The errors I think were just page numbering and general stuff; and maybe you'll see the font is different.The old manuals were much better and larger with more emphasis on the theory of operation. When CSIII (i.e. 4310, PRS4500, etc..) came out, the manuals became very thin with much less information.For many years customer support was handled locally via phone, email, and 24/7 cell, with both sides having technical discussions trying to walk customers through issues in hopes of solving the problem without returning the unit.In later years they decided to let new hires support the product. They got "trained" for about two-days on what a Cesium unit is and how to support every make/model (and not just Cesium - everything, including units that had custom settings/functions per individual customer needs); then moved support to CA. This timeline is basically when manuals became much lighter and phone support was more or less taking customer information so they can immediately issue an RMA.Also, in CSIII, the 9.192GHz is generated differently. Old style uses a multiplier and the new style is technically a divider. I could be wrong, but you won't find much information regarding this design; and the oscillators switched to 5MHz.On a side note, it was stated at one time not to bang the unit when the tube is hot because the ionizer could break. I forgot the time frame to allow the unit to cool, but it's good practice to leave it to cool. I think this was more regarding shipping the unit and the banging that occurs such as boxing and stacking it onto a delivery truck.

author: ITDH
author_rank: Contributor
timestamp: August 06, 2025, 02:03:56 pm
content: Components arrived and I rebuilt the PCB last night - replacing all the CMOS logic IC, UART, PIA, the failed SRAM and added PLCC / DIL sockets etc.The logic IC tested OK when removed from the PCB - but after being stressed by overvoltage I'd not trust they will still meet there original performance or trust in there long-term reliability.Failed parts so far found on the Servo board:-74HC7465764 (SRAM)1uF 35V Tant Cap.Finger's crossed when I test later this evening - I wonder how its going to go!!! will I be in luck? - I'd not bet on it!!!

author: ITDH
author_rank: Contributor
timestamp: August 07, 2025, 11:33:22 pm
content: Progress update on my FTS4040 repairs - this CS clock is now just playing with me!So after rebuilding the PCB and replacing the SRAM I have for the first time a initialization LEDand after say 10 minute's the unit goes to lock) for a couple of seconds then Major faultCommunication with the Monitor3 is very hit and miss as on each powerup or Reset the Baud rate is different - I've even seen a instance when the RX / TX Baud rate differed, and the Clock select pins to the HD-4702 is constantly changing during TX / RX (or this could have been happenstance - but for sure they where alternating at a constant cyclic rate).The EEPROM is also starting to full with what appears as nonsensical data - I'm presuming some memory field is related to the serial Baud rate - is it possible to have different Baud rate for TX / RX modes?When the unit briefly locked, I noticed a large frequency error in the 10's of Hz... which then had me doubted my GPS locked lab standard. I opened Lady Heather and YES my GPSDO was indicating PLL unlocked (plenty of active satellites) - sure enough the VCXO DAC was at 97% meaning the Samsung STP2945 LF OCXO in the GPSDO had drifted too far off frequency for the GPSDO to compensate... I did a quick search and others had reported the same issue with this OCXO. There is no accessible trimmer to re-center the OCXO frequency - so the OCXO is dead. I'll have to order a replacement from eBay.I'm lucky that I had Leo Bodnar's Mini Precision GPS Reference Clock on hand to use as a temporary replacement - these are great little units and "just work", Highly recommended as a "simple and affordable" GPSDO.So - one dead OCXO... I don't know why, but I then removed the Datum 1111B (HP 10811 "type" OCXO) from the FTS4040 and decided to test it on the bench.On first power up with 24Vdc the OCXO heated with 520mA current that quickly dropped to 28mA - but 10's of Hz negative Frequency offset - and each time I powered the OCXO from cold the time required for initial heating appeared to be getting shorter and shorter.I could find no information on the Datum 1111B - so having nothing to work with and no clue, I opened the Oscillator and started from basics...The HP 10811 should heat at a current limited 500mA which then drops to around 120mA when reaching operating temp - however the 1111B is a different design so I was not sure how relevant this is.SC cut crystals are very temperature sensitive and have turn-over point around 85Deg - my 1111B was internally marked with as 82.1Deg. For sure my "oven" was nowhere near 82 DegC and even with a negative 10V on the VC pin I could not pull the Frequency to 10MHz... (the 5045 servo controller can pull the OCXO VC pin about +/- 4500mV).Having little to work with, I started by removing the Semi-conductors and Tantalum Capacitors to measure them out of circuit - when I noticed this:-As I was desoldering the Tant Cap. (C11) I noticed that the Positive band was connected to the Ground plane!! hold on there's no negative supply in the 1111B? Looking closer to the silkscreen markings and YES the Tantalum had been fitted in the wrong orientation from the factoryI quickly traced out the circuit and sure enough the Tant Cap. formed an RC filter on the Gate of MOSFET in line with one arm of the Temperature compensation Bridge.. I'm guessing as part of the current limiting circuit.I replaced the Tant cap - reassembled the unit and and on testing I measured 520mA on power up - which then after a few minutes reduced to about 110mA just as the frequency was nearing -0.5Hz offset. I trimmed the OCXO to 10MHz with -410mV on the VC pin, and the oscillator was nice and stableSo in one day I've had 2 bad OCXO's - Surely I'm being Trolled by OCXO's here!!So does the unit work now? -Off Course Not!!! - with no apparently difference - looses lock after 1-2 seconds after coming out if Initialization (and with a large frequency offset)...However, I now believe that the original problem (where the unit would randomly start to loose lock) was the failing OCXO - and not the PSU. Sure the capacitor's in the PSU where in a bad way, and sure the unit has been subsequently further damaged due to the failed PSU repair - but I now believe that the OCXO was the initial culprit.I'm at a bit of a loss ATM - I'll give it a break for awhile to gather some thoughts and ponder my life choices - I also need to get to the root cause of the misbehaving MCU section.

author: edpalmer42
author_rank: Super Contributor
timestamp: September 22, 2025, 10:56:25 pm
content: Oh, the drama!A month ago, a Datum 4040A/RS sold on ebay for $1300 with a guarantee of full functionality. Today, I see the same seller is selling the same model. The pictures show the same serial number, but the new description doesn't mention a guarantee. But both auctions are listed as 'used' rather than 'parts'.I wonder if the unit is working......Hmmmmmmm.....