Repair : TEMEX/SpectraTime LPFRS/LPRO 10MHz Rb generator [got GPSDO to cal] - Page 1
Forum section: electronics / repair

author: TiN
author_rank: Super Contributor
timestamp: December 18, 2015, 05:30:58 pm
content: Assome may know already, due to f1lthy xmas time now I jumped into time-nuttery. What else it is, if one who don't even have frequency counter (any!) buys no less than five broken rubidium standards? Oh, well..Units in topic are TEMEX / SpectraTime LPRO, which are basically LPFRS with heatsink and little coupling PCB. Quick googling revealed next useful links:http://www.spectratime.com/products/isource/http://www.egidy.de/temex_lpfrs_lpro/https://www.eevblog.com/forum/projects/building-a-rubidium-freqency-standard-at-home/http://time-nuts.febo.narkive.com/ssfEAnts/temex-lpfrs-01-analog-frequency-adjustementHere's what I received today (lightning fast DHL shipment, yesterday I paid for them, today 3pm I got them delivered!).Rather bulky and heavy things, 500gramms each. I still confused about purpose of those heatsink fins and frame, as whole thing is ovenized, so why to add extra mass?All five are same units, with minor changes in labels, specced to power at +24VDC, have 10MHz output and RS232 TTL interface, as well as adjustment and lock pins.Removing some screws allow to easily take mu-shield off:Two rather dense populated PCBs interconnected by in-core flexible layer and mechanically locked together via Rb chamber outer case.Chamber is heater from both sides with TO-220 FETs.Here's look on PCB from outer sides:And inner sides:Motorola 68000 series MCU, DAC8800 and bunch of logic chips around.Closeups..There are two XO's glued to side of Rb chamber, 20.000MHz (bigger can) and 90MHz (smaller can in center). Some SMT trimpots and adjustable inductor(?) are nearby as well. Smaller part of chamber is lamp, bigger one is Rb cell with photodetector.How do I know? Well, I turned this one in to see magic atomic glow...In darkness:It's not so bright, but definately visible in normal dim room lights.I tried connecting serial console to it, set speed 1200 bps, 8N1 mode, but only garble came out:Where should I start this repair? I tried 3 modules , two drift hundreds of hertz in just seconds, compared to my 33120A, and lock never come low, while one is locking (signal goes low) but still drifts.Chassis getting about +50-53°C, and power current stabilize at about 0.515Amps with +20VDC (don't have powerful enough +24v source).As usual, full worklogwill be here.

author: MadTux
author_rank: Frequent Contributor
timestamp: December 18, 2015, 05:54:20 pm
content: Cool that you also bought someand did a teardown. So the possibility of successful repair increases massively for me, especially with your great PCB reversing skills.Mine haven't arrived yet, but I have some nice tools to repair microwave electronicsThey look quite nice and well laid out, from the inside. Maybe start with measuring ripple on tantalum/electrolytic caps?

author: TiN
author_rank: Super Contributor
timestamp: December 18, 2015, 06:01:15 pm
content: You reverse Rb side PCB, i reverse digital PCB, deal then!I have nothing for microwave, just 4GHz scope and some 8GHz probes. I can try 16G scope in theory, to measure Rb cell output?

author: MadTux
author_rank: Frequent Contributor
timestamp: December 18, 2015, 06:12:00 pm
content: I'll try my best,I have HP 8566&8568 spectrum analyzer, EIP microwave counter, HP 8684 microwave cavity oscillator that covers the 6.835GHz rubidium transition frequency and some more lower RF frequency generators.But not much digital gear, mostly stuck with my oldish analog Tek scopes

author: TiN
author_rank: Super Contributor
timestamp: December 18, 2015, 06:13:17 pm
content: Here's what happening in first tests:

author: edpalmer42
author_rank: Super Contributor
timestamp: December 18, 2015, 06:40:46 pm
content: I've never worked with that model of Rb standard, but all the other ones I've seen follow the same pattern so here goes.The heat sink is necessary to keep the electronics cool for long reliability. There are typically two, maybe three ovens. The main two are for the Rb lamp (~140C) and the Rb cell (~85C). Those temperatures are higher than most other Rb standards, but they're listed in the manual. The light from the Rb lamp shines through the Rb cell to a photocell so they'll be at opposite ends of that brass cylinder. The point where you can see the light is the break between the two. If there's a third oven, it's a normal quartz OCXO. Most Rb standards don't bother with this. Check the temperatures of those ovens. If they're out of spec nothing will work right.The second point is the Rb lamp. You've shown a picture that shows at least one of them has a working lamp so that's good. Whether it's quite right or not will have to wait until you get the serial port working.The third main point is that you should see the output sweeping up and down in frequency over a range of a few hundred Hz or so. It might take 30 - 60 seconds for a sweep. If the quartz crystal has aged enough that this sweep range doesn't include 10 MHz, the unit won't lock. Look for a trimmer to adjust the frequency. It looks like this model uses the 20 MHz crystal and divides it by two. They control the crystal temperature by gluing (soldering?) it to the brass cylinder. Actually, the 85C temperature of the Rb cell is in the temperature range for an OCXO, so maybe that part of the brass cyclinder is the Rb cell. Drift on this oscillator is the most common failure I've seen in the units I've played with. I just looked at your video and it looks like the sweep is happening.The serial port may have been customized to a different speed. Use a scope to check the length of a bit to see if it's actually 1200 baud.Ed

author: TiN
author_rank: Super Contributor
timestamp: December 18, 2015, 06:46:51 pm
content: Checked serial, it is 1200 Hz indeed, but inverted (idle bus stays low). I'll add inverter and try tomorrow. 3am here already...

author: MadTux
author_rank: Frequent Contributor
timestamp: December 18, 2015, 11:13:44 pm
content: According to this document, your LPFRS SN #7694. #7731 and #7894 must be in perfect working orderhttp://www.spectratime.com/documents/lpfrs_failure_rate.pdfSN first op h7695 27.06.03 121927731 20.06.03 123607894 24.11.03 8592But that was 10 years agoAlso interesting:http://www.spectratime.com/documents/life_mtbf1.pdf

author: PA0PBZ
author_rank: Super Contributor
timestamp: December 19, 2015, 10:40:40 am
content: Quote from: TiN on December 18, 2015, 05:30:58 pmI think you should correct that before anything else.

author: daqq
author_rank: Super Contributor
timestamp: December 19, 2015, 11:14:44 am
content: QuoteTry looking at it with a scope - if there is any weird processor communication timing issue (or a different baud rate), the baud rate might be well of. The fact that it sent out SOMETHING means that something is working there. Also, if the unit wants 24V I suggest you give it to it - the heater may not be powerful enough to work of such a derated voltage... or something else might disagree.Offtopic: Seeing your previous (and amazingly beautiful) precision voltage sources, I'm guessing that your next purchases will include a dewar, 70+GHz frequency source referenced to 10MHz and a bunch of Josephson junctions?

author: TiN
author_rank: Super Contributor
timestamp: December 19, 2015, 11:23:14 am
content: Serial comms fixed, with simple 74HCT14 between Rb and UART-USB.Code:TNT/LPFRS01 Rb Version 2.05 1/2/02 Checksum: 1D1A/E98100F8?00F880 84 62 38 1E 93 A5 E47E 7F 62 39 1F 8C A0 D47D 79 62 39 1E 93 9A D37C 7B 61 39 1E 93 9A D380 81 62 39 1E 97 A0 E480 6A 62 39 1F 99 A2 E47D 78 62 39 1E 9A 9B DB7E 6A 62 39 1E 98 99 DE80 7A 62 39 1E 9A A3 E67E 7D 62 39 1E 8A A3 DAI also took apart all modules. Nothing visibly blown inside. They are made in 2002-2004 per datecodes, and 4 are older revision, while one is newer (bit changed in layout, photos above are for newer one).Lamps on 4 modules are OK (at least I can see them glowing). (did not test 5th yet).Crystals 20MHz and 90MHz are working..Heading now to local market for 24V power supply.Temperature on lamp side (smaller section of physics chamber) is about +95C, photocell side about +75C (open case, no cover).

author: PA0PBZ
author_rank: Super Contributor
timestamp: December 19, 2015, 12:13:58 pm
content: QuoteVCXO Control (4th param, 38-39) seems stable, so I wonder if the output was also stable at that point.

author: TiN
author_rank: Super Contributor
timestamp: December 19, 2015, 05:29:30 pm
content: Bought Meanwell 24V/5V 4.6A dual PSU, now output seem to be 10.000000MHz (at least very close matching that value on HP 33120A generator now).Capturing serial logs for modules (status command every second), and will hook four Rb's together on scope to see if I can sync them...Maybe they are not so broken after all?

author: dundee
author_rank: Regular Contributor
timestamp: December 19, 2015, 05:35:37 pm
content: Quote from: TiN on December 19, 2015, 05:29:30 pmThat would be great news, TiN!Thanks for your efforts! I'm waiting for my standards..

author: TiN
author_rank: Super Contributor
timestamp: December 19, 2015, 11:48:08 pm
content: Hooked Rb's to SMPS DC/DC (Meanwell RD-125B, 24V 4.6A + 5V 4.6A).Three modules lock in and stay very close together, according to scope. Triggered on CH3.Two others are way off.Sorry for lab mess, I was tinkering with all this whole night... Going bed now (7:47am).~0.5Amps taken from PSU after warmup. Rb cell temperature +85-88°C (no case).Here are serial logs:Module S/N 340AModule S/N 7011Module S/N 7011 adjustmentModule S/N 7731I got some video footage on this too, will cut it and upload later.

author: TheSteve
author_rank: Unknown
timestamp: December 20, 2015, 12:13:36 am
content: Did you leave the working ones running overnight with the scope set to infinite persistence?

author: TiN
author_rank: Super Contributor
timestamp: December 20, 2015, 12:16:12 am
content: No, i will put them into cases first.

author: lukier
author_rank: Unknown
timestamp: December 20, 2015, 12:25:12 am
content: 3458A is upside down in hope to reverse the drift?

author: MadTux
author_rank: Frequent Contributor
timestamp: December 20, 2015, 02:42:48 am
content: Quote from: TheSteve on December 20, 2015, 12:13:36 amNice if you have such a great scopeDoes anyone know a program which can do webcam snapshots periodically (WinXP, or better Linux)? My idea is to mount a webcam in front of my old Tek7904A with 2x 7A26 in chopped mode and then take snapshots periodically. Then use imagemagick to logic OR all images => analog digital persistence scope

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: December 20, 2015, 03:06:49 am
content: Quote from: MadTux on December 20, 2015, 02:42:48 amRaspberry PI + camera and Tektronix C-5CSet up a cron job to take a snapshot as often as needed.http://www.netinstructions.com/automating-picture-capture-using-webcams-on-linuxubuntu/

author: MadTux
author_rank: Frequent Contributor
timestamp: December 20, 2015, 06:43:24 am
content: Quote from: ManateeMafia on December 20, 2015, 03:06:49 amI have no operational RPi and noTek C-5C, but I have Thinkpad X61s, some black cardboard, some old craptastic Logitek webcam and my awesome shellscript skript kiddie skillsI found fswebcam to work quite nicely, so I used it for the shellscript sample below: (you have to install some libs, if you install the latest 2014 version of fswebcam from source on old linux like my Ubuntu 10.04)So, here the shellscript sample, it even worksCode:initialtimestamp=$(date +%s)piccount=1 #image counter, set 1 initially, dont set zero, or it will crash!picdelay_sec=10 #delay between images, fswebcam needs some time for each pic, say 10-15sa=1 #need this shit apparently so that nested loops work :)b=2 #otherwise first "done" breaks down everything :(while [ $a -le $b ]dotimenow=$(date --rfc-3339=seconds)timestamp=$(date +%s)customtime=$(date +%Y%j%H%M%S)next_pic_time=$(( initialtimestamp + piccount *picdelay_sec ))(( piccount++ ))echo "time $timenow"echo "timestamp $timestamp"echo "custom timestamp $customtime"echo "picdelay $picdelay_sec"echo "initial timestamp $initialtimestamp"echo "next pic time $next_pic_time"while [ $timestamp -le $next_pic_time ]dotimestamp=$(date +%s)doneecho "Cheeze :) $timestamp"echo "next pic time $next_pic_time"fswebcam -r 640x480 --jpeg 80 test$timestamp.jpgdoneIt takes unix timestamp, compares that to some timestamp in the future, waits until that time is reached and then takes a picture with fswebcam. Loops restarts after that. With 40kB per image (640x480), it can take lots of scope images until HDD is full.Depending on how fast your computer is, you can set pic delay as low as 2 or 3 seconds, my old thinkpad needs some more time.

author: dundee
author_rank: Regular Contributor
timestamp: December 21, 2015, 05:54:27 pm
content: Hi Guys!My rubidiums arrived today (Germany) -that was really fast.I only had time for a fast check. 2 Rubidiums lock in after a few Minutes.The other three ones not. No time for more testing at the moment

author: TiN
author_rank: Super Contributor
timestamp: December 22, 2015, 12:58:31 am
content: Cool. Are they same as mine?I see at least someone have freq. counter.Seems I got hooked, BG7TBL GPSDO board on it's way...

author: TheSteve
author_rank: Unknown
timestamp: December 22, 2015, 01:05:26 am
content: Quote from: TiN on December 22, 2015, 12:58:31 amWhich one did you get? The original one isn't a perfect 10 MHz, it is closer to 9.999 999 999 8 Hz which is very easy to see compared to a Trimble GPSDO etc.

author: TiN
author_rank: Super Contributor
timestamp: December 22, 2015, 04:37:09 am
content: Pic on eBay shows one with Trimble labelled OXCO. Will see what one exactly will arrive.

author: TheSteve
author_rank: Unknown
timestamp: December 22, 2015, 04:55:31 am
content: Quote from: TiN on December 22, 2015, 04:37:09 amThat one will work fine. I use the same gpsdo, I just mounted it in a box myself.

author: dundee
author_rank: Regular Contributor
timestamp: December 22, 2015, 07:05:44 pm
content: Quote from: TiN on December 22, 2015, 12:58:31 amYesConnected today the unlocked led as described in the manual. My led is not going off (lock). But the frequency is fineon this device. Hmm...

author: TiN
author_rank: Super Contributor
timestamp: December 23, 2015, 04:13:21 pm
content: How you know frequency is fine?.Hooked one of "good" Rb's to run last night. Attached RS232 data, samples every second.

author: PA0PBZ
author_rank: Super Contributor
timestamp: December 23, 2015, 04:33:05 pm
content: Quote from: TiN on December 23, 2015, 04:13:21 pmDid you notice that some parameters are reversed? Like photocell DC Voltage is 0 - 5V for FF to 00, and in your picture I see it start at the highest value, which is unlikelyAlso the heating currents are reversed.

author: TiN
author_rank: Super Contributor
timestamp: December 23, 2015, 05:57:53 pm
content: Woops, u right.Heating currents already correct. 2am here, my bad

author: MadTux
author_rank: Frequent Contributor
timestamp: December 24, 2015, 05:42:03 am
content: Well guys, my rubidium standards are now finally back in SwitzerlandAnd I have a few good ones too, didn't have time to test them all, though.Good thing is that there is still plenty of rubidium left in the lamps. I disassembled one unit that didn't lock and looked at the lamp and there is a big blob of rubidium visible in the back.It's easy to reassemble it back, you only have to push both the lamp and the rubidium cell back into that middle piece and solder the wires back in.But before I do that I want to see whether I can reverse engineer the driver electronics and make the lamp run without the the rest of the assembly to take some pictures of that awesome rubidium glow. It looks really cool IRL (somewhat similar to potassium, which isn't surprising) unfortunately most cameras are unable to capture the full spectrum (looks far more purplish/red IRL). Tomorrow I'll compare phases of a few rb-standards over long time on my Tek scope to see how accurate they are. Maybe I can score a cheap 1PPS GPS receiver sometimes and use it as trigger source.BTW, the coil for the inductively coupled rubidium plasma bulb runs at 147.4 MHz, with a few sidebands. (used a wire loop to pick up the magnetic field at the wires)And that addon PCB inverts the lock signal: (wasn't already mentioned, so I thought I add it)9 pin Sub-D pin 3: => 5V if locked, 0V if unlocked10 pin rectangular connector on addon PCB: => 0V if locked, 5V if unlockedDo I need a level shifter for RS-232 (from PC)? IIRC, RS232 from PC is +/-15V, while the LPFRS says it wants TTL (0/5V).But now I have to go sleeping, it is already dawn outside

author: SeanB
author_rank: Super Contributor
timestamp: December 24, 2015, 06:24:54 am
content: Probably yes, a level shifter and inverter, as RS232 is negative as logic 1, and TTL versions are 5V as logic 1. Easy with a simple MAX232 chip, which will do both the generation of the 12V rails using some capacitors, and do the inversion as well. If you want to do it on a PC without RS232 ports use a cheap FDTI chip, which does TTL levels as standard. Just get the real chip, or fix the driver so it does not brick the clones.

author: TiN
author_rank: Super Contributor
timestamp: December 24, 2015, 11:43:42 am
content: QuoteSounds familiar.You will need simple inverter and logic-shifter (5V->3.3V) if you use USB-UART like I do.Thanks for teardown of phy module.Do you plan to open cell section too?I'm curious what that adjustment screw does near xtals.

author: MadTux
author_rank: Frequent Contributor
timestamp: December 25, 2015, 04:25:35 pm
content: Got the lamp running. The complete oscillator is in the physics package, a couple of capacitors and BLV21 power VHF transistor behind the rubidium bulb. Schematics comes later, have to go to boring christmas lunch first.Used a Schottky diode in TO220 for heating, damn efficient these things, the cables from the PSU got hotter than the diode. A reverse protection diode might also be nice, because the HP E3616 sometimes went into overvoltage mode as the lamp ignited. Probably some reverse EMF when the magnetic field suddenly changes as the lamp ignites.

author: TiN
author_rank: Super Contributor
timestamp: December 25, 2015, 05:52:58 pm
content: Here's schematics of LPRO adapter board, which is in place between RBXO in LPRO versions we talking about here..

author: TheSteve
author_rank: Unknown
timestamp: December 25, 2015, 06:57:34 pm
content: Bought a 5 pack - so I'm in too!

author: PA0PBZ
author_rank: Super Contributor
timestamp: December 25, 2015, 07:19:18 pm
content: Quote from: TheSteve on December 25, 2015, 06:57:34 pmI almost did, but decided to ask the seller about the shipping cost first. What did you guys pay?

author: TheSteve
author_rank: Unknown
timestamp: December 25, 2015, 07:26:43 pm
content: Quote from: PA0PBZ on December 25, 2015, 07:19:18 pmShipping to Canada was quoted at $110.00 USD so I shipped them to my US address which was 50 dollars.

author: edpalmer42
author_rank: Super Contributor
timestamp: December 25, 2015, 09:48:23 pm
content: Quote from: TheSteve on December 25, 2015, 07:26:43 pmI don't know why he insists on using such a high-priced shipping method. It makes most of his stuff uneconomical to me and I've told him so.Ed

author: TiN
author_rank: Super Contributor
timestamp: December 26, 2015, 07:21:32 am
content: 50$, DHL here. Good thing, it took only overnight to get it here (TW) last friday, so I could play on weekend. Sometimes it's worth it

author: TheSteve
author_rank: Unknown
timestamp: December 29, 2015, 06:30:22 am
content: Received my 5 units today. Powered them up one at a time. The first 3 all seems to behave exactly the same. When powered up the frequency is about 200 Hz low. Then you can see the frequency go up but it never quite gets to 10 MHz, at the same time the current drops.The 4th unit is similar but starts about 400 Hz low.The 5th unit is actually generating a 10 MHz signal but it isn't as stable as it should be I don't think and the lock indicator never toggles.Let the games begin.Also received another GPSDO today, now I have three of them running - good thing they are cheap!EDIT:Just messing with one here.If I just power one up it does what appears to be a bit of a half hearted effort to find 10 MHz but doesn't really cycle much. It just settles at 9.999823 MHz. However poking around with it open does cause it to do a proper cycle above and below 10 MHz - it even looks like there is a brief pause as it passes 10 MHz but it keeps going and eventually settles at 9.999823 MHz again. I believe the Peak voltage of Rb signal is too low and it never finds the proper dip it needs. The level I am seeing it only 0x20 or so which should be very close to the .6 volt minimum.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 29, 2015, 09:29:33 am
content: The behavior if the first 3 units is about what one can expect from a unit that is not working anymore: The current goes down as the internal temperature gets close to staedy state - thats perfectly normal. The internal PLL tries to get lock, but never gets to the right frequency. Chances are that the internal VCXO has drifted too nuch to reach the right frequency. This might be relatively easy to fix by adjusting the coarce tuning so it starts closer to 10 MHz.

author: TheSteve
author_rank: Unknown
timestamp: December 30, 2015, 02:53:48 am
content: What is odd about the units is that they "think" they are locked even though they are all off frequency. They are even all similar in that they think they are locked at 9.999823 MHz or so. If I adjust one of the pots I can make it ramp the frequency up and down forever, and it does pass 10 MHz. The range is from 9.999540 to 10.000120 MHz but it never locks/stops. Pretty easy to see it isn't centered around 10 MHz.btw I tried the course electronic frequency correction but it is only good for +- a few Hz.After the reading the manual I also directly connected the serial port to a USB to RS232 converter - yes technically it is out of spec but they recommend trying it in the manual. It works great and is nice and simple.I will say that if/when someone figures out the problem with one it will fix probably 90% of the bad ones out there.edit:Just playing around, the GG values typically sits at 02 or so when it is hunting. When it finds a lock at 9.99982x MHz there is an increase in signal to around 20, sometimes higher - so it really is thinking it "sees" a valid Rb peak. I wonder if this much frequency error could be caused by a drive problem with the C Field drive coil - if it is weak perhaps the resonant frequency of the Rubidium spectral line separation has that much error. If we think about the division needed only a very small error at 6.8x GHz will cause a big problem at 10 MHz. My other thought is that the rubidium cells have become contaminated internally shifting the resonance point.I also notice that the last value (AA) which is the 90 MHz power control signal seems too high on all of mine. It needs to be stable between 2 to 4.5 volts yet I am seeing values Dx to Fx - which would be at the high end of the range or in most cases out of range. Maybe the BLV21 transistor is weak - or that is the circuit that has drifted.Fired up the spectrum analyzer - no signals detected around 147 MHz as someone else had posted.thoughts???

author: edpalmer42
author_rank: Super Contributor
timestamp: December 30, 2015, 05:02:14 am
content: Generally, if an Rb standard thinks it's locked, it is! Have you compared the frequency to one of your GPSDOs? If you have a time-interval counter and two units that both seem to be off-frequency, use the counter to compare them. If possible, collect the data electronically and process it with a program like TimeLab. The difference between a pair of defective standards and a pair of working standards should be pretty dramatic. You could also compare one Rb unit to your GPSDO. Just remember that a GPSDO has it's own 'signature' that will appear in the data.Here's a message that I posted a while ago that shows a comparison between two Rb standards.https://www.eevblog.com/forum/beginners/help-me-understand-allan-deviation-measurements/msg801113/#msg801113Ed

author: TheSteve
author_rank: Unknown
timestamp: December 30, 2015, 05:20:46 am
content: They are most certainly wrong - I have multiple GPSDO standards that I know are good. The Rb locks at over 180 Hz low which is a massive error.

author: edpalmer42
author_rank: Super Contributor
timestamp: December 30, 2015, 06:18:00 am
content: Frequency isn't the only thing to look at. Regardless of the actual value, is the frequency stable? Really stable with good Allan Deviation? Then itislocked, regardless of the value. Are you going to try to fix an RF problem when the fault is actually in the frequency steering or DDS circuitry?You mentioned the effect of the frequency error between 6.834 GHz and 10 MHz, but you didn't get it quite right. A 177 Hz error at 10 MHz would cause a frequency error of about 121 KHz at 6.834 GHz. That's not going to happen. There's no way that the unit would detect a signal that it thought was valid.The C-field isn't the problem. It provides a very small frequency adjustment and no matter how badly it was fried, it couldn't cause the measurement you're seeing. Notice that the resolution of the C-field adjustment is shown in the spec sheet as 1e-11 per step as compared to the coarse frequency adjustment resolution of 1e-9 per step.Your GG value of 20 is lower than the manual says it should be, but I don't know what that mean in terms of a circuit fault. What are the values of the other parameters?Ed

author: TheSteve
author_rank: Unknown
timestamp: December 30, 2015, 06:51:36 am
content: No the frequency is not as stable as it should be.(I don't think anyway) However the unit is finding something it likes, it will hunt up and down and find the same frequency each time. The GG value also increases when it thinks it has found lock - the lock indicator often toggles as well. I was pondering the potential frequency error and at 6 GHz the error is huge as you say. I wasn't sure how much frequency change was possible via the C field but it makes sense it is a very small amount.Here is a log from one of the units in question:2B 0B 5D 44 80 D7 2B D331 0A 5C 4D 80 D4 30 E133 0A 5C 55 80 CA 35 D332 0E 5D 5C 80 CE 33 E434 0C 5D 64 80 D1 3D E337 10 5D 6A 80 C6 39 E23B 0E 5D 71 80 C1 45 D33D 0C 5D 77 80 C5 4F CF3D 0A 5C 7D 80 C0 44 E13F 1F 5D 83 80 C9 52 E03F 2B 5D 82 80 C7 57 E144 25 5D 82 80 BC 5F D043 1F 5D 81 80 C2 60 E248 2B 5C 81 80 B1 5A DA48 27 5D 81 80 C0 6A DB4A 25 5D 81 80 B9 70 D54C 1F 5D 80 80 B6 74 D44E 27 5D 80 81 B5 78 D54F 2A 5D 80 81 B3 7C DB52 24 5D 80 81 A7 80 D1As the GG value increases from 1x to 2x is when the unit sweeps up in frequency and hits 9.999,817,1xx,x MHz at which point it indicates lock and stops there.Just tested a second module, it stops at the same frequency, the lock indicator toggles and but eventually the GG value goes below 20 and it indicates unlocked again.Third module shows the same behavior and frequency except it indicates it is locked and stays locked with a GG value in the 4x range.-hmm, just had a small earthquake-Forth module shows the same behavior and frequency, GG is under 20 so it indicated unlocked5th module is does everything the same but it actually locks at 10,000.000.0xx.x MHz, it indicates locked but then the GG value falls below 20 and it indicates unlocked.

author: Vgkid
author_rank: Super Contributor
timestamp: December 30, 2015, 08:02:46 am
content: How is the power supply doing for those units? Have you monitored it.

author: TheSteve
author_rank: Unknown
timestamp: December 30, 2015, 08:17:23 am
content: Quote from: Vgkid on December 30, 2015, 08:02:46 amI haven't gone over it in great detail - would be nice to have a known working unit to compare to. My scope is currently in use monitoring my new GPSDO. I do see significant AC on some caps with my DMM. The 5 volt line looks good.edit:Did some quick bodge work and paralleled a few extra caps with the existing electrolytic units and now one of the units that was outputting 9.999,817 is magically giving me 10.000,000,0xx.x MHz and indicates it is locked. The Rb signal is still quite low though. The AC that was on the caps was up to 1 Vpp @ 125 kHz(internally used frequency).So at this point, I'd say replace all 4 electrolytic caps and then see if they all work

author: edpalmer42
author_rank: Super Contributor
timestamp: December 30, 2015, 03:33:51 pm
content: Quote from: TheSteve on December 30, 2015, 06:51:36 amFor those playing along at home, these values represent the outputs of the following parameters:HH GG FF EE DD CC BB AAHH (Photocell voltage) is low, but rising and nearing the acceptable range so the lamp might be okay. As this voltage rises, I'd expect to see GG increase as well.GG (Rb output signal) is low. Just about anything could cause this.FF apparently doesn't mean anything.EE (VCXO control voltage) looks good. It stabilized in the middle of its range.DD (Analog Frequency Control Voltage) doesn't appear to be connected. It looks like it's internally biased to the middle of its range.CC (Rb lamp heating current) seems to be wandering a bit. The manual says that it varies with ambient temperature. I don't know if that level of variability makes sense or not. Variations in the lamp temperature could affect the GG value.BB (Rb cell heating current) looks like it was still warming up when this data was collected. If it stabilizes, it should be okay.AA (90 MHz power control) is moving from 4V1 to 4V5 which is at the top end of its acceptable range.Since it looks like the unit was still warming up when these values were collected, I can't say that anything here is obviously wrong. Even the GG values are trending in the right direction. All I can suggest at this point is to let the unit run for an hour and see what the readings are and whether they are stable or wandering. I'd expect them all to stabilize with no more than maybe a couple of points of jitter. Over a long period (days or weeks) you may see a slow change in a few of them.If you haven't already done so, try the C00 and F00 commands to return the center frequency to the factory default value. I realize that your frequency error is far larger than these commands can set, but it might reset some other internal parameters. Can't hurt!Ed

author: TiN
author_rank: Super Contributor
timestamp: December 30, 2015, 04:57:46 pm
content: Here's datafrom one Rb which I have running since 23 December 24/7, in case one want to reference..Still waiting for GPSDO to compare with.

author: edpalmer42
author_rank: Super Contributor
timestamp: December 30, 2015, 09:35:28 pm
content: Thanks TiN, that's helpful. I browsed through your data and came up with the following info:Desired MeasuredHH - 66 to B2 - 7D to 81 perfectGG - 33 to A8 - 15 to 2E lowFFEE - 66 to B2 - 55 to 53 perfect - slight downward trend due to xtal aging - their range is unnecessarily tightDDCC - 1A to E6 - 6F to 81 perfectBB - 1A to E6 - 95 to AB slight downward trend indicating rising lamp temperature (?!)AA - 66 to E5 - DC to EF at the top of the rangeSeems like a unit that has had a long life but still has some life left in it. You might eventually have to figure out which trimmer adjusts the xtal frequency to raise the EE value. I don't know what to make of that downward trend on the BB value. Maybe it's just taking a long time to stabilize.Steve, once your unit(s) has stabilized, you can compare it to these numbers. Your values may be different from TiN's, but the range of the values should be similar.Ed

author: TheSteve
author_rank: Unknown
timestamp: December 30, 2015, 10:04:27 pm
content: I've only opened one unit so far but am 100% sure they all need new caps which have been ordered and should be here tomorrow. Based on the behavior I am seeing I suspect they will all generate 10 MHz after the cap change. At that point I will let them run much longer and post some data.The one I did put some used caps in already looks a million times better but is running wide open on the bench so any temp change alters the frequency. I also consider it the experimental one so I don't mind adjusting the various pots/trimmers to see if we can improve some of the measured parameters.edit - I already played with the C00 and F00 values, on my units the course is 0, the fine has some very small corrections added.And I found which pot brings the GG value up - it only takes the smallest tweak to go from from a 2x value to a 4x value - not saying the tweak is legit but it gives me hope we can possibly eek more life out of these units.

author: edpalmer42
author_rank: Super Contributor
timestamp: December 30, 2015, 10:30:56 pm
content: How big a frequency change are you seeing? Since the temperatures are measured by a thermistor and controlled by the micro, I wouldn't expect much change. Try dropping an old towel over the board. Does that reduce the frequency variation?Ed

author: TheSteve
author_rank: Unknown
timestamp: December 30, 2015, 10:36:04 pm
content: Quote from: edpalmer42 on December 30, 2015, 10:30:56 pmThe frequency change is +- 10 milliHz - measured using an 53132A locked to a nice stable GPSDO. You can see it compensate for it instantly by watching the current drain.

author: edpalmer42
author_rank: Super Contributor
timestamp: December 31, 2015, 02:50:04 am
content: Quote from: TheSteve on December 30, 2015, 10:04:27 pmSounds good!As you say, it's hard to know if the tweak is legit, but if they put a pot there in the first place it must have been to set the level. After many years at an elevated temperature, it might have developed a bad contact. So, how could restoring the level be bad?That's my story and I'm stickin' to it.Ed

author: dundee
author_rank: Regular Contributor
timestamp: December 31, 2015, 04:13:14 pm
content: I've found this caps:http://www.ebay.de/itm/231766325218?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AITDatasheet:http://www.mouser.com/ds/2/427/118aht-239891.pdfLooks like a good, high quality replacement cap.

author: PA0PBZ
author_rank: Super Contributor
timestamp: December 31, 2015, 06:39:24 pm
content: Quote from: TheSteve on December 29, 2015, 06:30:22 amYes, 9.9998224 here, at least the first one I tested. Let's see what the others can do.Edit: I tested 3, one was ok and the other 2 settle at around 9.99982. Tested the caps in one of the failing ones and yes, they are gone. ESR of 5.5R is about 10 x too much.

author: TheSteve
author_rank: Unknown
timestamp: January 01, 2016, 05:13:30 am
content: Here are some notes and data on all five of my units - all have been running great for several days now after the fixes/tweaks noted below. I have also power cycled and cooled them and they all lock within seconds of each other.Borrowed one of TiN's pics to mark some *possible* adjustment points. The board layout on the unit pictured may not match yours perfectly however the pots are all the same even if the 4 caps that need replacement are not.-The point marked GG appears to set the Rb signal level - if you think you need more Rb level you can tweak it slightly while watching the serial data.-ADJ. B - is the pot I adjusted very slightly to get one unit that was showing a very low Rb level to suddenly jump back to life and lock. No idea what it really does. If turned too much you will lose lock-ADJ. C - no idea what it does. I did adjust it and didn't see any change in the serial output levels but changing it too much will cause lock to be lost.So I recommend the following:-Power up each unit and verify they output something close to 10 MHz-Replace the four 47uF 35v volt caps - this is mandatory! I used radial caps instead of axial as high quality ones are much easier/cheaper to source. It was easy to fit them in.-Fire up the units and see what they do. If they lock at 10.000,000,xxx,x they are doing well - let them warm up a little and if the GG level is really low(like 20 or less) and you're feeling adventurous give it a small tweak to bring the level up to 4x or so. Levels below 20 may show 10 MHz but the lock indicator may toggle or not be stable.If they don't lock then you may want to give ADJ. B and/or possibly ADJ. C a very small tweak - make note of the original positions!Some other notes:-If you find the unit tough to get apart try prying gently at the edges of the serial port.-I had to drill a few screws on the big outside heatsink that were seized. There were really cheap screws on some and stainless steel on others.-The units have a SMT 2 amp fuse internally, no comment on how I know this, lol. If you're unit appears completely dead check this!-The outside pot can adjust the unit very precisely, as can the eeprom fine and course adjustments. You'll need a really good reference to fine tune them.-All of my units now start at 9.999,500 MHz +-200Hz when powered on, the frequency tends to go down every so slightly as it warms up. When the Rb lamp fires I tend to see a very slow increase in frequency that gets faster over time. Eventually it gets really fast and should lock as soon as it hits 10 MHz - working units will not ramp past 10 MHz and then lower the frequency again, they will lock first shot.-If you turn the GG level up too high you may see the unit lock/unlock/lock/unlock cycle a few times before staying locked. The GG level tends to start quite high and drops when the units reach full temp. If the level is too high I think it confuses the unit before the level drops.-When a unit is working properly it should lock and stay locked, no flickering or toggling of the lock indicator at all.-All five of my units have the course electronic adjustment set to zero, all of them have some small tweaks to the fine electronic adjustment.-You can safely connect the serial connections direct to a standard RS232 uart/serial port.-I added a third picture showing where accurate sources of TTL level 5 MHz, 10 MHz and 20 MHz square waves can be found if needed.-Added 3 pics showing the output on my spectrum analyzer with a 30dB attenuator inline - all 5 units look identical. Spec is 0.5 Vrms output which is 6.99 dBm so the output level is bang on.Results for each of my units(as pictures below):unit #5:This unit has had the 4 caps replaced and the magic pot tweaked a little.Putting out a stable looking 10 MHz - 10.000,000,001,x - with 1 second samples from my 53132A with GPSDO reference the frequency is only changing +- 1mHz.Serial output:79 62 C3 96 85 67 AE DB79 61 C2 96 86 68 AD DC79 63 C2 95 86 68 AF DD79 62 C2 96 86 69 AE DD79 61 C2 95 86 67 AF DC79 48 C1 95 86 68 AE DC79 64 C2 96 86 68 AE DC79 64 C2 95 86 69 AE DD79 64 C2 95 86 68 AF DC79 62 C2 96 85 68 AE DB79 64 C2 95 86 68 AE DCunit #4:This unit has had the 4 caps replaced, no other changes made.Putting out a stable looking 10 MHz - 10.000,000,001,x - with 1 second samples from my 53132A with GPSDO reference the frequency is only changing +- 1mHz.Serial output:8A 75 C3 A8 6E 74 AF DB89 73 C2 A8 6E 73 AF DB8A 71 C3 A8 6E 74 AF DC89 71 C3 A8 6E 73 B0 DB8A 72 C2 A8 6E 73 AF DC8A 73 C2 A8 6E 74 B0 DB8A 71 C2 A8 6E 72 AF DB8A 73 C2 A8 6E 72 AF DC8A 74 C3 A8 6E 72 AF DC89 71 C3 A8 6E 73 B0 DC89 6F C3 A8 6E 74 B0 DC89 71 C3 A8 6E 74 AF DDunit #3:This unit has had the 4 caps replaced and the magic pot tweaked a little.Putting out a stable looking 10 MHz - 10.000,000,001,x - with 1 second samples from my 53132A with GPSDO reference the frequency is only changing +- 1mHz.Serial output:78 53 BF C1 62 7E B3 DD77 4F BF C1 62 7E B3 DD77 3A BF C1 62 7E B2 DF77 53 BF C1 62 7F B3 DC78 54 BF C1 62 7E B2 DD78 53 BE C1 62 7E B2 DE78 51 BF C1 62 7F B2 DF78 55 BF C1 63 7F B3 DE78 54 BF C1 63 80 B3 DF78 54 BF C1 62 7F B3 DD78 53 BF C1 62 7F B2 DE77 54 BF C1 63 7F B3 DE78 55 BF C1 63 7E B2 DF78 3A BF C1 62 7F B2 DCUnit 2:Caps changed but still no lock at all. It does show a hint of a Rb signal as it passes 10 MHz during a sweep but is very weak.UPDATE - made a small tweak to what I have labeled ADJ. B - and it has locked just fine ever since. It is almost like the pot was just dirty and needed a hair movement to be make contact again the change was so small. This unit appears to be the weakest in the bunch as the AA level is high.Serial data:7A 4C C5 B1 87 68 AE E17A 4B C5 B1 87 69 AE E27A 4F C5 B1 87 68 AD E27A 4F C5 B1 87 68 AE E17A 51 C5 B1 87 67 AD E27A 4C C5 B1 87 68 AE E17A 51 C5 B1 88 69 AE E27A 4C C5 B1 87 68 AE E27A 4F C6 B1 87 67 AD E27A 52 C5 B1 87 68 AD E27A 4A C5 B1 87 68 AE E17A 51 C5 B1 87 68 AE E17A 50 C5 B1 87 68 AE E17A 51 C5 B1 87 68 AE E2Unit 1:Caps changed and locks with a solid looking 10 MHz - it is wide open on the bench still as my test unit though so no stability can yet be judged. I am sure it will be fine though.UPDATE - all reassembled and running great so far.Serial data:8A 3E C3 B4 6D 72 A8 DB8A 43 C3 B5 6D 71 A8 DC8A 44 C3 B5 6D 71 A8 DC8A 44 C3 B5 6D 71 A8 DC8A 45 C4 B5 6D 72 A9 DB8A 45 C3 B5 6D 72 A8 DC89 43 C3 B5 6D 71 A8 DD89 2E C3 B4 6D 70 A8 DD89 43 C3 B5 6D 70 A8 DC8A 43 C3 B5 6D 72 A9 DB89 44 C3 B5 6D 71 A8 DC8A 3E C3 B5 6D 72 A8 DB89 43 C3 B4 6D 72 A8 DD

author: edpalmer42
author_rank: Super Contributor
timestamp: January 01, 2016, 07:52:37 am
content: You know, you're not really getting the best results out of your 53132A. Since you're measuring 10 MHz, you're limited to 100 ns resolution when you measure frequency. If you put your GPSDO into channel 1 and the Rb into channel 2 and then measure time interval, you'll be using the full 150 ps resolution. Collect that data via the RS-232 port or GPIB port and you'll get more precise results.Measuring frequency also averages the measurement over the gate time which can make things look better than they are. Measuring time interval can be set to measure only one interval so there's no averagingEd

author: TheSteve
author_rank: Unknown
timestamp: January 01, 2016, 08:09:53 am
content: Quote from: edpalmer42 on January 01, 2016, 07:52:37 amWill do! I figure I should let them bake some more before trying to see how they are really doing. I currently have 3 GPSDO's and one of the Rb's connected to the scope with infinite persistence to see the drift.Anyone have a script ready to go that would do the job? I can do it via serial or via a Prologix GPIB adapter or even an Agilent USB to GPIB depending on the software package required. I'd prefer to just use the windoze box I have handy, but using a Pi is also possible.

author: TiN
author_rank: Super Contributor
timestamp: January 04, 2016, 04:25:38 pm
content: I've got my GPSDO.Now it seems to need antenna, as it refuses to work with random stub antenna (likely GPRS), giving Operation alert : Antenna.Let's crack GPS receiver hood open:Bundled PSU is 6VDC 2.5V brick.Three SMB to SMA-female pigtails were included.Module itself using Xilinx Spartan XC3S50 FPGA (U10), ISSI SDRAM, MXIC Flash with sticker 75292-00 and TI TMS320 processor. RS232 interface is converted via SIPEX SP3232E to unpopulated J5 connector. I hooked my Silabs CP2103 USB-UART to pins 11 and 12 instead.There is unpopulated SMT connector on bottom side, perhaps JTAG?All connected, and shield back in place:Close-up on LDO and GPS chipset:Serial logs:Code:UCCM-P >*IDN?TRIMBLE,57964-80,50693553,V2.0.1.6-01Stats:Code:UCCM-P >SYST:STAT?-------------------------------------------------------------------------------57964-80 serial number 50693553 firmware ver 2.0.1.6-01 LINK mode-------------------------------------------------------------------------------Reference Status __________________________ Reference Outputs _______________XX Ref 8KHz 0: XX Ref 8KHz 1:  TFOM 2 FFOM 3XX Ref 8KHz 2:  UCCM A Status[OCXO WARMUP]XX Ref 8KHz 3: XX GPS: [No Ref]ACQUISITION .................................................[GPS 1PPS Invalid]Tracking: 0 ____ Not Tracking: 12 _______ Time ____________________________PRN El Az C/N PRN El Az GPS 00:01:29 (?) 22 Aug 19995 -- ---20 -- --- ANT DLY -1 ns22 -- --- Position ________________________2 -- --- MODE Hold12 -- ---13 -- --- LAT N 25:57:29.65830 -- --- LON E 119:31:14.77932 -- --- HGT +39.66 m (MSL)1 -- ---18 -- ---26 -- ---29 -- ---ELEV MASK 5 deg-------------------------------------------------------------------------------Coordinates are somewhere in China, so those are old ones, tested by seller.Need bodge up GPS antenna , I assume..Code:- UCCM Slot STATE-1-1. #Now ACTIVE STATUS ---------------- [OCXO Warm]1-2. #Before ACTIVE STATUS ------------- [OCXO Warm]2-1. #Reference Clock Operation -------- [Not Used]2-2. #Current Reference Type ----------- 2-3. #Current Select Reference --------- [GPS 1PPS]2-4. #Current Reference Status --------- [Ref LOS]#GPS STATUS ----------------------- #Priority Level ------------------- [LINK > GPS]#ALARM STATUS#H/W FAIL [ GPS LINK ]#OPERATION ALARM ------------------ 3-1. #PLL STATUS ----------------------- 3-2. #Current PLL MODE ----------------- [OFFSET OBSERVATION MODE]POSSTAT:Code:UCCM-P >POSSTAT---------------------------------------------08/22/1999 00:09:40---------------------------------------------Position: LAT(N 25:57:29.658) LON(E 119:31:14.779) H( +39.66 m MSL)---------------------------------------------Geometry: PDOP(0.0) HDOP(0.0) VDOP(0.0)num of visible sats > 0num of sats tracked > 0-------- Receiver Channel State --------CH 0 > SateID(25) TrackMode(tracking ) SigValue( 0)CH 1 > SateID(19) TrackMode(tracking ) SigValue( 0)CH 2 > SateID(22) TrackMode(tracking ) SigValue( 0)CH 3 > SateID(02) TrackMode(tracking ) SigValue( 0)CH 4 > SateID(31) TrackMode(tracking ) SigValue( 0)CH 5 > SateID(07) TrackMode(tracking ) SigValue( 0)CH 6 > SateID(28) TrackMode(tracking ) SigValue( 0)CH 7 > SateID(17) TrackMode(tracking ) SigValue( 0)CH 8 > SateID(15) TrackMode(tracking ) SigValue( 0)CH 9 > SateID(04) TrackMode(tracking ) SigValue( 0)CH 10 > SateID(24) TrackMode(tracking ) SigValue( 0)CH 11 > SateID(09) TrackMode(tracking ) SigValue( 0)---------------------------------------------Rcvr Status(1):---------------------------------------------Antenna Voltage: 5000.00mV , Antenna Current: 2.13mA

author: PA0PBZ
author_rank: Super Contributor
timestamp: January 04, 2016, 04:46:48 pm
content: Quote from: TiN on January 04, 2016, 04:25:38 pmIt measures the current to the assumed pre-amp in the antenna, but...QuoteSo how did you do that?

author: TheSteve
author_rank: Unknown
timestamp: January 04, 2016, 04:55:17 pm
content: Quote from: PA0PBZ on January 04, 2016, 04:46:48 pmHe used the command "posstat".

author: TiN
author_rank: Super Contributor
timestamp: January 04, 2016, 04:55:37 pm
content: I did nothing, just hooked cable to antenna port.

author: PA0PBZ
author_rank: Super Contributor
timestamp: January 04, 2016, 07:52:30 pm
content: What I mean is that when you hook up a random antenna (piece of wire) I don't expect any current to flow, hence the Antenna alert.But in the status it shows 2.13mA, something I don't expect on a random piece of wire.

author: TheSteve
author_rank: Unknown
timestamp: January 04, 2016, 08:00:04 pm
content: Quote from: PA0PBZ on January 04, 2016, 07:52:30 pmI don't think the antenna current drain sensor is that accurate, it just gives a rough value.

author: PA0PBZ
author_rank: Super Contributor
timestamp: January 04, 2016, 08:03:40 pm
content: Quote from: TheSteve on January 04, 2016, 08:00:04 pmSure, but it is there to warn you about damage like a broken preamp or cable, so it should not read 2mA on an open or short.

author: edpalmer42
author_rank: Super Contributor
timestamp: January 04, 2016, 09:28:47 pm
content: Quote from: TheSteve on January 01, 2016, 08:09:53 amSince Timelab supports the 53132A, I'd recommend it rather than any kind of script. It supports GPIB (not sure about the Prologix adapter though), serial, and TCP/IP so you should be able to get something working.Ed

author: Theboel
author_rank: Frequent Contributor
timestamp: January 07, 2016, 01:00:25 am
content: Hello All,is this same seller sold Yours rubidium oscillator :http://www.ebay.com/itm/Lot-of-5-LPFRS-01-Rubidium-Frequency-Standard-AS-IS-Condition-/272086453625?hash=item3f599dcd79:g:7uEAAOSwCQNWfJUC

author: TheSteve
author_rank: Unknown
timestamp: January 07, 2016, 01:05:00 am
content: Yes, that is the listing.

author: PA0PBZ
author_rank: Super Contributor
timestamp: January 07, 2016, 07:52:32 pm
content: I replaced the caps in one of the units that showed 9.99982 MHz and it immediately started to behave again. Both caps on the logic pcb where completely gone, showing 3 and 8uF. The 2 on the other (analog?) board looked reasonable but I replaced them anyway.

author: edpalmer42
author_rank: Super Contributor
timestamp: January 07, 2016, 08:53:38 pm
content: What are the date codes on these units that have failed caps? I realize that these units run hot, but it still surprises me that these caps are failing and causing problems. What brands are the failed caps? Do the good units use the same brand?Ed

author: TheSteve
author_rank: Unknown
timestamp: January 07, 2016, 08:56:19 pm
content: I believe these units all are from the 2001/2002 time period. You can actually see the ship date on every unit they made it seems:http://www.spectratime.com/documents/lpfrs_failure_rate.pdfI know all 5 of mine are in that list.I have been using Timelab to log the time interval between two of the Rb units and to log the interval between a GPSDO and an Rb unit. Will post some data soon.

author: Orange
author_rank: Frequent Contributor
timestamp: January 07, 2016, 09:07:04 pm
content: Quote from: edpalmer42 on January 07, 2016, 08:53:38 pmThe blue ones are BC components caps. This brand was a former Philips cap. I also see LL (LongLife) on the caps, and 125 deg. Celsius.Philips caps are known to be very good. It is not the usual china junk. However after perhaps 10 years of use these things also die. No cap can survive that long in a 100 deg. Celsius environment. It is funny that the manufacturer is concerned about the depletion of the rubidium in the lamp, while the design has a much bigger risk of failing (the caps), which is well known.....

author: PA0PBZ
author_rank: Super Contributor
timestamp: January 07, 2016, 09:51:04 pm
content: Quote from: edpalmer42 on January 07, 2016, 08:53:38 pmthe unit I replaced the caps on has serial # 7902, delivery date 24.11.03 according to the document.The caps are black, 47uF, 35V 105C, not sure what brand they are, it has a rhombus shape with dots where the lines connect.

author: shempe
author_rank: Contributor
timestamp: January 08, 2016, 12:48:27 am
content: Quote from: dundee on December 31, 2015, 04:13:14 pmNice find, thank you. I bought a few for my Units.But beware, the wire´s are 0,8, better use some with 0,6 like the BX Series from nichicon in these units.With a little bit creativity, a la "cut the old one out and and solder the new caps to the old wires" it works.Here another PDF about this Unit:https://www.denk-stein.com/pdf/fp/lpro-en.pdf

author: TiN
author_rank: Super Contributor
timestamp: January 08, 2016, 05:11:44 pm
content: Bought simple GPS antenna.QuoteCode:Command completeUCCM-P >POSSTAT---------------------------------------------01/08/2016 17:04:39---------------------------------------------Position: LAT(N 25:57:29.658) LON(E 119:31:14.779) H( +39.66 m MSL)---------------------------------------------Geometry: PDOP(0.0) HDOP(0.0) VDOP(0.0)num of visible sats > 3num of sats tracked > 3-------- Receiver Channel State --------CH 0 > SateID(01) TrackMode(tracking ) SigValue( 0)CH 1 > SateID(03) TrackMode(tracking ) SigValue( 0)CH 2 > SateID(22) TrackMode(tracking ) SigValue(29)CH 3 > SateID(08) TrackMode(pos avail) SigValue(39)CH 4 > SateID(16) TrackMode(pos avail) SigValue(33)CH 5 > SateID(32) TrackMode(tracking ) SigValue(24)CH 6 > SateID(27) TrackMode(pos avail) SigValue(35)CH 7 > SateID(19) TrackMode(tracking ) SigValue( 0)CH 8 > SateID(09) TrackMode(tracking ) SigValue( 0)CH 9 > SateID(07) TrackMode(tracking ) SigValue(21)CH 10 > SateID(30) TrackMode(tracking ) SigValue( 0)CH 11 > SateID(11) TrackMode(tracking ) SigValue(20)---------------------------------------------Rcvr Status(0):---------------------------------------------Antenna Voltage: 5000.00mV , Antenna Current: 13.24mALocation still incorrect, will see how it goes tomorrow morning..Antenna just fixed 30 cm from window outside, don't have other way, it's apartment on 10th floor.

author: TheSteve
author_rank: Unknown
timestamp: January 08, 2016, 05:38:49 pm
content: TiN,Use the command - SYSTem:PRESet to get the GPS to perform a full survey of your location.

author: TheSteve
author_rank: Unknown
timestamp: January 08, 2016, 05:41:09 pm
content: Here are some results of 8 hour time interval plots from my HP 53132A comparing my Nortel(Trimble) GPSDO to one of the rubidium units and comparing two rubidium units to each other. Each plot was run twice.

author: edpalmer42
author_rank: Super Contributor
timestamp: January 09, 2016, 03:31:34 am
content: It looks like something is degrading your results. The 53132A has a resolution of 150 ps. This should give you a one second result of 1.5e-10 but you're seeing more like 6e-10 and it's consistent through all the tests. If you haven't done so, check the noise floor of your 53132A by connecting a signal to the Ch1 input through a T connector and a cable to Ch2. Set Ch1 to 1 Mohm and Ch2 to 50 ohm. Measure the time interval from Ch1 to Ch2. Make sure that the cable doesn't move or change temperature during the test. If that test is good, now you're into the black arts of AlDev measurements. Ground loops, power supply coupling, injection locking, external and internal interference, stray sunbeams or other temperature changes, etc. After all, we're mucking about in the PPT area. Be sure to think positive thoughts! Try to stay at least 2 meters away from the equipment during the measurements. No, I'm not kidding! (about the 2 meters - not sure about the positive thoughts, but it can't hurt)The Rb-GPSDO tests are about what's expected. Looks like there was some warmup and stabilization between the two tests. GPS performance can be broadly defined as a line that goes through 1e-10 @ 100 sec. and goes both up and down 1 decade for each time decade. Notice that your results turn down and to the right to follow this line. Different GPSDOs will take a slightly different path, but they all run parallel to the 'GPS line'.Your Rb-Rb results are also about what's expected. The manufacturer only specs out to 100 sec. as 2e-12 and you're in that ballpark from 1000 sec. on.Did you do the Rb-Rb tests first? I see that the first Rb-GPSDO test bottomed out at ~1e-12 while the second one kept on going down. Something improved between the first and second test. Did you make any changes in your setup, cables, power supply, anything?The graph always shows the performance of the worst of the counter, the GPSDO, and the Rb. So below about 20 sec., your counter is blind to the performance of either the GPSDO or the Rb. All you're seeing is the counter's performance. At about 20 sec. the GPSDO's performance becomes the dominant factor. But the Rb is so good that you don't start to see it until you get to about 1000 sec. and even that may be misleading. The red line that keeps going down at the right side of the graph is following the GPS performance. The only way it could do this is if the Rb was better than the GPS. Otherwise, the red line would turn and run horizontal like the others.So, if you really want to find out the performance of your Rb units, more investigation is required. You might discover that Rb 4 is somewhat better than the others. Such things do happen.Ed

author: TheSteve
author_rank: Unknown
timestamp: January 09, 2016, 04:32:11 am
content: Thank you for your feedback. There were no changes between any of the tests other then time of day and probably a 5 degree C temperature drift up and down throughout the day/night. Everything was powered on the entire time. However I was certainly closer then 2 meters and other gear was switched on and off, including signal gens. There are 8 sources of 10 MHz running right now - three GPSDO's and 5 Rb's all quite close. I also have no control over what my 20+ pound Bengal cat does while I'm at work. For all I know he could think the Rb's are paw warmers. The biggest factor is likely the 53132A itself. It is calibrated however the fine interval step was skipped as it needs a very specific HP setup - so that may be ruining the noise floor.edit:Looked into the fine time interval calibration further. It is a 4 step process with the HP 59992A time interval calibrator generating 4 signals. The first two are 10 Mhz square waves in phase and the second two are 10 MHz square waves out of phase. I am not sure what the specific differences are between the measurements which appear the same. The calibrator documents don't give any detail, it just says they are in phase signals. Anyway, this may be something I can generate at some point.I also did more testing to try to get closer to the potential noise floor of the 53132A itself. Feeding in a test 10 MHz square wave cut the noise floor to 3e-10. If I feed in a test 1 MHz square wave it is 1.63e-10. I'll have to ponder how the input frequency relates to the noise floor. I think the biggest difference would be if all of my signals were square waves, right now all GPSDO's and Rb's are sine.

author: TiN
author_rank: Super Contributor
timestamp: January 10, 2016, 04:20:04 pm
content: Replaced capacitors on two modules.Rb cell value on one of them instantly jumped to 8A-8E value ranges.Second one I trimmed to ~4x Rb cell value.Adjusted both modules after lock to GPSDO, using scope (used both coarse and fine registers using UART) to get minimum phase drift.But it's tricky. Also I'm not so sure GPSDO output is good, it sees only 4-5 sattelites. Perhaps I need better antenna?Red - GPSDO, Blue and green - two RB's. 10 min, infinite persistance.XY-mode:RMS Jitter of RB units is ~1ns, while GPSDO output is ~2.2ns

author: edpalmer42
author_rank: Super Contributor
timestamp: January 10, 2016, 05:14:06 pm
content: Quote from: TheSteve on January 09, 2016, 04:32:11 amI'm not familiar with the details of the 53132A. If the fine time interval calibration is intended to reduce the internal noise, then it's important in this situation. If it ensures accuracy of the measurement then it probably won't have much of an effect. Absolute values aren't important here.Square waves definitely give better results when you're approaching (or exceeding!) the limits of your measuring equipment. Trigger noise is something that you always have to keep in mind in these situations and square waves help minimize it. You can also use the cable test that I described earlier to make sure that your counter doesn't have any white noise issues. As the test runs, the graph keeps going lower and lower in a straight line. If it gets down below levels you're concerned about then you're good. If the counter has some white noise issues on the input, perhaps due to a wounded but not killed input stage, the graph will turn and become horizontal.Another thing you should do in Timelab is check the phase and frequency graphs. If there are anomalies or glitches there, your AlDev results are suspect. Save your data and then try to edit the phase or frequency graph to remove the problems. Once both graphs arre clean, your AlDev results should be valid. It's also helpful to post the .TIM file so that others can see and play with your data.Ed

author: Orange
author_rank: Frequent Contributor
timestamp: January 12, 2016, 07:11:32 pm
content: I received a batch of five yesterday. First replaced all the caps, some of them where toast, mainly the black ones. The blue ones were not really bad, still high ESR of 0.8 ohms.After some testing I have now 4 units working sort of. On one unit there is some LF phase noise...I did some probing on the board, and I think I have found the Rb demodulated signal. At least this is what it looks to me. Referring to pot-meter designations.I think the following functions are:Pot A : Output signal level of the detector. I have set this to aprox 3..3.5 Vpp after tweaking all other potsPot B : I believe this the SRD diode bias, it behaves like this, and is fairly critical to set (CCW is a good starting point)Pot C : Some sort of AGC for the RF level, fully clock wise is the safest I foundPot D: No idea, perhaps an detector balance signal, but you can tweak it on the Rb signal. It was set to mid position for largest Rb signal.Update: One of the units did not get it to 10.000 MHz during the lock sweep. I changed the crystal for a new one (ordinary 20MHz type) and that made it work :-)It was glued with Sikaflex (Swiss made polyurethane kit)....Updated picture of TiN with potmeter locations

author: jpb
author_rank: Super Contributor
timestamp: January 16, 2016, 04:19:47 pm
content: I've been following this thread with interest, wondering whether to join in or not (i.e. buy a set of 5).The postage to the UK would be $80 so the cost for 5 would be $129 + $80 + 20% (Inport Duty or VAT) which is around $250. I guess replacing the caps/other bits would be around $10 per unit and not all of them would be repairable. So though the process of restoration looks fun and satisfying it is a largish investment and a bit of a gamble if they require more than just a change of caps to get them functioning properly.Given that I have very little time at the moment and don't really have any space (I'm in between house moves living in small rented space with my equipment all in boxes) I suspect the sensible thing would not to acquire yet more stuff to carry around but you all seem to be having a lot of fun.How are the restorations going and can anyone say what fraction of their lot of 5 are repairable, function ok?

author: TheSteve
author_rank: Unknown
timestamp: January 16, 2016, 10:09:08 pm
content: All five of mine are working great. I've run them on and off to see how they lock from cold etc - always perform exactly as expected. If I log them with my 53132A they all look good. I'd think you have extremely good odds of easily getting 3-4 of the 5 working, if not all 5.

author: jpb
author_rank: Super Contributor
timestamp: January 16, 2016, 10:15:38 pm
content: Quote from: TheSteve on January 16, 2016, 10:09:08 pmThanks for the feedback.I feel very tempted - though if I get them they will probably need to sit in a box for a few months until I get my lab back.

author: jpb
author_rank: Super Contributor
timestamp: January 16, 2016, 11:24:07 pm
content: Quote from: PA0PBZ on January 07, 2016, 09:51:04 pmLooking at TiN's photos the blue caps are 63V 85C / 40V 125C. So perhaps the later units had upgraded temperature ratings? Also It is hard to find Caps at that Voltage and temp that are 0.6mm lead diameter. Looking through Farnell there are some very expensive Vishay ones but they are only 0.6mm up to 35V and then are 0.8mm and they are very expensive (but 20,000 hours at 125C presumably mean they are pretty robust):http://uk.farnell.com/vishay/mal212310479e3/cap-alu-elec-47uf-35v-axial/dp/2407388The 0.8 mm 63V 125C ones are less than 1/4 the price and 8000 hours at 125C seems reasonable:http://uk.farnell.com/vishay-bc-components/mal211838479e3/cap-alu-elec-47uf-63v-axial/dp/1695292

author: jpb
author_rank: Super Contributor
timestamp: January 16, 2016, 11:47:56 pm
content: Quote from: Orange on January 12, 2016, 07:11:32 pm0.8 ohms seems pretty low given that high temp (125C) Vishay caps list a ESR of over 2 ohms on the data sheet. So it looks as if the blue (40V 125C) caps were ok while the black (35V 105C) ones were not up to the job.

author: Orange
author_rank: Frequent Contributor
timestamp: January 17, 2016, 09:21:31 am
content: The design got upgraded during their life. The old units have black caps of really poor quality, they are also 85 deg types with 0.6mm leads. The PCB is also designed for this. You can fit 0.8mm caps in it, but need to suck the solder very good out of the hole.The latter production ones have bigger holes, adapted for the 0.8mm leads.I used 100uF/63 volts, 85 deg. types from Philips, which I had at hand. the ESR of those are 0.22 Ohms. I don't mid to replace the caps in a few years from now if they should go bad.Old units can be identified by the stickers on it with a Tekelek Aitronic logo.Mind you that the design requires low ESR types, since some of these caps are used in a switched mode set-up with a 125KHz freq. (See manual, general description)I'm not sure if the Farnell types can be placed in this design looking at their ESR (2.xx Ohms). If all of this becomes an issue you can also put in radial caps from Nichicon or Panasonic. The voltage on one of the caps is 24 Volts, other run at 16 volts... So 35Volts for the caps are a minimum I would say.

author: TiN
author_rank: Super Contributor
timestamp: January 17, 2016, 11:18:00 am
content: I used radial 105C caps instead, there is still plenty space inside Rb to fit standing radial caps.Will post more details after get back to it, bit busy with voltnut projects for now.

author: jpb
author_rank: Super Contributor
timestamp: January 17, 2016, 07:08:16 pm
content: I see the same seller also sells a lot of 5 without the heat sinks for the same price. These have the same label on the front as the 2011 datasheet - I don't know if this means they are any newer?I now can't decide which of the two sets to order.http://www.ebay.com/itm/Lot-of-5-LPFRS-01-10M-Rubidium-Frequency-Standard/252232382829?_trksid=p2047675.c100005.m1851http://www.ebay.co.uk/itm/272086453625?_trksid=p2060353.m1438.l2649Everyone on here has ordered the ones with heatsinks - was this just a random choice?

author: edpalmer42
author_rank: Super Contributor
timestamp: January 17, 2016, 07:24:55 pm
content: Same price for 5 units. Same stupid shipping cost even though the weight will be substantially less. But now you have to find your own heatsink. Doesn't seem like a good deal to me.Ed

author: Orange
author_rank: Frequent Contributor
timestamp: January 17, 2016, 07:50:18 pm
content: The ones without heatsink are the older ones, since they have the Tekelek Airtronic logo on them.At one point Tekelek Airtronic sold the TEMEX subsidary (TEMEX Neuchatel Time TNT)http://www.spectratime.com/product_downloads/4g_sro_pr.pdfTNT became TEMEX TimeTEMEX Time was again renamed to Spectratime....http://www.orolia.com/pdf/TemexTime%20_changes_name_toSpectraTime.pdf

author: TheSteve
author_rank: Unknown
timestamp: January 17, 2016, 08:32:55 pm
content: When we bought them originally the non heatsink version wasn't even listed. Being the heatsink version is not only newer but also that a heatsink is required I'd still go for the heatsink version.And at this point I think its fair to say most can be easily fixed.

author: jpb
author_rank: Super Contributor
timestamp: January 17, 2016, 10:02:45 pm
content: Thanks everyone for the info.So the heatsunk ones are the better buy.

author: jpb
author_rank: Super Contributor
timestamp: January 18, 2016, 08:21:55 pm
content: I have just ordered and paid for a set. By the time postage and tax/import duty is added the price doubles but it should still be a bargain as long as at least a couple of them can be got working.

author: jpb
author_rank: Super Contributor
timestamp: January 21, 2016, 07:53:21 pm
content: Mine arrived today, but sadly it may be a week before I can get to play with them properly.Meanwhile I've been setting up an Alan Deviation kit in terms of my old TTi TF930 counter (my new Tek one is hundreds of miles away at my mother-in-law's house), my Agilent 33522A, a mini circuits mixer and low pass filter and some home-brew software. I'm quite pleased with the noise floor (using the "reference" as input) see attached. Of course things might be very different when I try doing it with two real devices. (And I don't yet know if I can get them working.)The plan is to use one as a reference for the 33522A and the counter and the other one fed into the mixer and the output of the mixer going via the filter to the counter the difference frequency of 10Hz seems to work best. (The plot was this setup except using the 33522A's internal reference for it and the counter and feeding this via a splitter to the mixer as well.)Edit: I add a photo of the setup.Edit : EdPalmer42 has kindly pointed out that my numbers are probably unbelievably good, and I agree with him that they need investigation. My 1 second value of 1E-13 in particular. Please note though that I have plotted LOG(tau) so that 1 on the x axis is 10 seconds not 1 second.I'll remove the plot until I can come back with more realistic results or at least have thoroughly checked my code and workings.Edit again - Correction! (Thanks Ed). I've rechecked my code which I originally wrote for frequency measurements but then put an option for period measurements. In one place I failed to do this correctly so I ended up having a factor of 100 error (roughly dividing by 10 instead of multiplying by 10). The graph is now rather more realistic - it is the same shape but shifted up by 2 (on the Log10 scale). I attach it.The ADEV noise floor is 10E-11 at 1 sec. My counter is quantised at 20 nsec (50MHz) but I gain a factor of 1E6 from the mixer but then lose some on the whole process. The 10Hz signal period is 100 mHz which is measured to around 10E-5 (orders of microseconds) so with the superhet factor this comes to around 1E-11 which all makes rather better sense.Hopefully when I get my good counter back (30psecs with back to back measurements of each period) I should be able to do a bit better.

author: jpb
author_rank: Super Contributor
timestamp: January 25, 2016, 10:29:09 pm
content: Changed the caps on my first one. It proved much more difficult than anticipated because my desoldering tool was clogged up and I was in a hurry.Put it back together with the heat sink back to front so I could get at the connectors and powered it up. The output was the correct level (0.5Vrms into 50 ohms) and the frequency started low and then went to something that seemed right. It measured a steady 10.00000050MHz on my counter - the error is in my counter I think but I'll need to get two going to compare and also compare to a GPS - perhaps at the weekend.Altogether pleased so far.

author: TheSteve
author_rank: Unknown
timestamp: January 26, 2016, 06:58:27 am
content: Quote from: jpb on January 25, 2016, 10:29:09 pmSounding pretty positive. If it isn't working the frequency error is generally enough to know its a problem. Have you connected a terminal/serial port to it yet, if not I recommend it so you can see the values.

author: Orange
author_rank: Frequent Contributor
timestamp: January 26, 2016, 02:09:28 pm
content: Let it run for a few days, and check again. I had one that seemed OK during the first 12 hours, but then it lost lock, and stayed at 10.000130The strange thing is that the lock indicator of this faulty one still said to be locked !!It is the only one that is not OK, so 4 out of 5. Not bad.In the mean time I have replaced the 85deg. caps for 105deg radial Panasonic FR caps (100uF/50Volts).Quote from: jpb on January 25, 2016, 10:29:09 pm

author: jpb
author_rank: Super Contributor
timestamp: January 26, 2016, 06:45:39 pm
content: Quote from: TheSteve on January 26, 2016, 06:58:27 amI plan to do so as soon as I get the time - it might not be until the weekend.Quote from: Orange on January 26, 2016, 02:09:28 pmThat is a little worrying, I'll leave it running for longer.I realise since posting that the frequency will be a little out as I've directly connected to the unit not via the little board which has a pot on it presumably adjusted to give an accurate 10MHz. My main concern is that it is steady. I'll worry about exact frequency when I get a chance to use one of my GPS units (I'm in rented accommodation whilst trying to move house so I don't have access to a lot of my stuff and can't really stick aerials up - though I can probably dangle one out the window.

author: Orange
author_rank: Frequent Contributor
timestamp: January 26, 2016, 11:05:29 pm
content: Quote from: jpb on January 26, 2016, 06:45:39 pmYes its really helpful if you have an accurate time-base. I use a rubidium time-base to my counter (a HP5384A and a HP53132A), which is calibrated against a GPSDO (Z3805). So any discrepancy in the milli Hertz domain is notified. The LPFRS has +/- 1 miili Hertz accuracy (10 seconds)

author: jpb
author_rank: Super Contributor
timestamp: January 30, 2016, 09:27:17 pm
content: After a bit of struggle, I've got my serial interface working - I had to reprogram my USB-RS232 module to invert the polarity and it still wouldn't work at all via PowerShell (which I use for my counter) so I had to resort to Putty.Here is a selection of warmed-up output:8D 50 BD B5 80 8C A4 DC8D 50 BC B5 80 8D A4 DC8D 51 BD B5 80 8D A4 DC8D 50 BD B5 80 8D A4 DC8D 4F BC B5 80 8D A4 DB8D 51 BC B5 80 8D A4 DD8D 4E BD B5 80 8C A4 DC8D 4E BD B5 80 8C A4 DB8D 4E BD B5 80 8C A4 DC8D 4F BD B5 80 8C A4 DC8D 50 BD B5 80 8E A4 DC8D 38 BC B5 80 8D A4 DB8D 4F BC B5 80 8D A4 DC8D 4E BC B5 80 8D A4 DC8D 51 BD B5 80 8D A4 DC8D 4F BC B5 80 8D A4 DB8D 38 BC B5 80 8C A4 DC8D 51 BC B5 80 8D A4 DC8D 50 BD B5 80 8D A4 DC8D 50 BC B5 80 8D A4 DC8D 4E BC B5 80 8D A4 DD8D 50 BD B5 80 8D A4 DD8D 38 BC B5 80 8C A4 DCSo the photo-cell DC voltage is 5V*(0xFF-0x8D)/256 = 2.23V which is in the range 2.0 to 3.5 but rather on the low side for my liking.The Rb signal level is dropping to 0x38 which is 1.1V which is in the range 1 to 3.3V but again rather low. It does cycle though in the range 0x38 to 0x51 or (1.1V to 1.6V).The VCXO voltage of 0xB5 is 3.53V so is just beyond the 3.5V upper limit.The Frequency Adjust voltage is 0x80 because it is currently not connected and I reset the unit.The Rb lamp heating limiting current is 500mA*(0xFF-0x8C)/256 = 225mA and is well between 1A and E6.The Rb cell heating limiting current is 500mA*(0xFF-0xA4)/256 = 178mA and is well between 1A and E6The total current the unit is drawing at present is 438mA which seems consistent with 225+178+something for the rest of the electronics.Finally the 90MHz power signal is fairly stable around 0xDC which is 4.3V which is just in the range 2 to 4.5V.So my conclusion is the unit is functioning but probably the lamp is old and perhaps the crystal has shifted in frequency.I have read about people rejuvinating lamps with a hot air gun - if I feel adventurous perhaps I'll try this at some point - meanwhile I've got another 4 units to sort out!PS: my unit takes almost exactly 5 minutes to lock (I timed it at 4:55). How does this compare with your units everyone? It seems about what I'd expect.The current draw on warm up is 1.3A which is rather high (the data sheet has 0.9A). 1.3A corresponds to 31W instead of the datasheet's 25W unless this is option code F or E but it doesn't say it is. The stable current is around 440mA which corresponds to 10.5W which is about right given that my house is relatively cold (around 18C).I see from the failure document posted earlier that my unit:7998 24.11.03 8592is roughly 12 years old and was operated for less than a year (if it was on continuously).The other units that I've yet to work on are:7499 23.07.03 115687594 01.04.03 14280and a couple not in the list:662Aand269C

author: jpb
author_rank: Super Contributor
timestamp: January 30, 2016, 10:35:02 pm
content: I just opened up unit number 2 and was horrified to see the screws and even the sma connecter were corroded and rusted and the physics unit looked in a bad way. It looks as if water leaked into it.So I decided to try it out before wasting any more time on it and amazingly the current draw etc seems normal and the after several minutes the lamp lit up! It doesn't lock but I've not yet changed the caps but it is looking much more hopeful than appearances would suggest.Changed the caps and fired it up and it doesn't lock.The HH value was way off but I reset to factory defaults and it is now more reasonable. I can see it sweeping up and down through 10MHz on a scope.Some sample warmed up but not-locked log values are:7B 00 B1 46 80 85 AF D97B 00 B0 3C 80 85 AE D87B 00 B0 32 80 84 AE D87C 00 B1 3D 80 85 AE D87C 00 B1 46 81 85 AF D97B 00 B0 4F 80 85 AE D87B 00 B0 59 80 85 AE D87B 00 B0 62 80 84 AE D97C 00 B1 6C 80 84 AE D87C 00 B1 78 80 84 AE D87C corresponds to 5V*(0xFF-0x7C)/256 = 2.56V which is better than my other unit and agrees with the fact that I physically saw the lamp light. The second 00 value corresponds to "warming up" but it has obviously reached temperature so it looks as if the Rb signal level is non-existant even though the dc level is ok??No change after leaving on over-night, looks like the RF (modulated 90MHz?) is not there.7C 00 B1 AD 80 86 AF D97D 00 B2 C3 80 85 AF D87D 00 B2 E2 81 85 B0 D97C 00 B1 CE 80 86 B0 D9

author: Orange
author_rank: Frequent Contributor
timestamp: January 31, 2016, 10:15:50 am
content: Quote from: jpb on January 30, 2016, 10:35:02 pmI also had one that had water damage, a lot of rusted stains all over the PCBs. Amazingly this one worked Ok after a CAPs change. I then cleaned it with alcohol.The physics package still has some corrosion stains on it, which I cannot get rid of.I think these things were stored in the rain somewhere.BTW I saw in some of the Datum LPRO manuals, that if they are damp, sudden frequency jumps can occur. So a good bake-out is needed

author: Orange
author_rank: Frequent Contributor
timestamp: January 31, 2016, 10:25:33 am
content: Quote from: jpb on January 30, 2016, 09:27:17 pmAll my units start at 1.3 .. 1.36 A. They settle at 0.51 A. This when they are mounted on a bigger heat-sink in addition to the original one.The data sheet is wrong, or these versions have an shorter lock time, which draws initially more power.

author: uncle_bob
author_rank: Unknown
timestamp: January 31, 2016, 07:24:16 pm
content: Quote from: Orange on January 31, 2016, 10:25:33 amHiApparently these were made for "a major telcom customer" (according to the failure data pdf). It's not at all surprising that a tweak or two got made to the design to accommodate whatever the customer needed / wanted / thought up.Bob

author: jpb
author_rank: Super Contributor
timestamp: February 01, 2016, 09:03:56 pm
content: After changing caps on all five my current standing is:Two good ones that lock at the right frequency (though one is getting rather old).One that locks to a fixed frequency but is way out (by several kHz so perhaps the crystal is duff and it is never reaching the dip - it perhaps is locking on a flat part of the absorption curve well away from the resonant part).Two ones that despite having good lamps don't lock at all and have zero readings for the rf lamp signal.I'm working on a proper zero crossing detector, but in the mean time here is an Alan deviation plot for my two good ones. The two curves are the measurements (upper), the measurements over sqrt(2) assigning equal noise to each (the lower) and the three crosses are the values from the data sheet.Given the crudity of the measurement I'm quite pleased with the agreement.

author: TheSteve
author_rank: Unknown
timestamp: February 02, 2016, 04:36:18 am
content: Have you tweaked any of the pots at all? One of mine didn't lock at all until I touched one of them. I guess I was lucky, all of mine work great and there was no water damage.

author: jpb
author_rank: Super Contributor
timestamp: February 02, 2016, 07:57:29 pm
content: Quote from: TheSteve on February 02, 2016, 04:36:18 amI messed around with the pots on one of the duff ones whilst looking at the output but it didn't improve it.My next step will be to try changing the crystals on one or two.I don't mind one duff one as I want to experiment with taking the bits out separately and perhaps using a separate ocxo (with some sort of interface circuitry) and it is easier to do that with one that is broken anyway. But 3 duff ones is a little high.I have reasonable hopes of getting the one with the off frequency working and perhaps the last two will end up just providing spares.

author: uncle_bob
author_rank: Unknown
timestamp: February 03, 2016, 01:54:19 am
content: HiA quick poke with a scope will tell you if the crystals are still running in the oscillators. The same sort of check will tell you if it's on frequency or not (maybe not quite a poke, but the same idea).Best approach is to take a working one and the dead one. Poke around and see what's not the same between them.Bob

author: Orange
author_rank: Frequent Contributor
timestamp: February 03, 2016, 06:47:35 pm
content: Buying these things is for sure a gamble. I have 4 working consistently after a lot of 'burn-in' hours. You are just unlucky with your batch.One of mine has a problem with the heating of the lamp and Rb cell. It jumps up and down with the temperature of both the lamp housing and also the Rb cell housing, and at some point completely runs away....Symptoms of this are an oscillating current draw from 0.6 to 0.23Since there are no schematics, it becomes almost impossible to do some fault finding....

author: jpb
author_rank: Super Contributor
timestamp: February 03, 2016, 06:52:56 pm
content: Quote from: uncle_bob on February 03, 2016, 01:54:19 amI did have a look with the scope and the crystals themselves seemed ok but were a little low in frequency (especially the 90MHz) but then the scope probes are providing capacitive loading so it is hard to know. I didn't do a direct comparison with a working unit because I didn't really want to take it to bits again in the time I had available.Looking at another thread on this forum I see that others have suffered from duff Step-Recovery-Diodes, if it is this then there probably is little hope in fixing it.But it is early days, I don't have time to do anything during the week and very little time at weekends so progress is rather slow - still it is educational!

author: jpb
author_rank: Super Contributor
timestamp: February 03, 2016, 06:58:40 pm
content: Quote from: Orange on February 03, 2016, 06:47:35 pmYou are right that it is a gamble but not a bad one. Even in my case I hope to have 3 good units at a cost of (excluding my time of course) of under £200 including the excessive postage and VAT whilst most units on ebay (which may not be that good anyway) seem to go for more than £100 each now-a-days so I have not really lost a lot and it is a very educational experience.Those with 4 or 5 good units have done very well.

author: jpb
author_rank: Super Contributor
timestamp: February 03, 2016, 09:07:13 pm
content: Further Alan Deviation measurements. Leaving the devices warmed up for a day and measuring over 48hours at 1Hz offset seems to give better results (I've yet to build my zero crossing detector but results aren't bad without it).I've just started a 48 hours measurement of the ref vs itself to get the noise floor.

author: uncle_bob
author_rank: Unknown
timestamp: February 04, 2016, 12:44:24 am
content: HiNot quite sure if this is a dupe or not (posted before it seems to have vanished ... if it is ...sorry !!).My load of Rb's got here today via DHL. They made it fine with no "lost in a snow drift" incidents. They were well packed and nothing seems to have been damaged in transit.One of the ones I got took a major hit to the connectors at some point in it's life. The DB-9 is pretty well caved into the front of the unit. I think I'll save that one to work on last. One other one has a couple of dings and may be rusty. I'll know better when I get it open. The serial numbers are all over the place. They seem to have been pulled at random from the same pile as everybody else's parts.A package from Mouser also got here today. I bought a batch of EGXL350ETD221MJ16S electrolytic caps. They are 35V 220uf 125C parts with a 1050 ma ripple current rating at 100 KHz. At 30 cents each, they were the best thing I could find. Based on a quick look, I think they will fit ok on the boards. They are radial rather than axial. I had zero luck finding anything with a rational ripple rating in axial (at least with my price limits). They have 0.6mm diameter leads so they should drop in fairly easily.======So after a bit of fun and games:Seven of the units came open. The one with the crushed front was one of those.The unit with the rust signs is indeed rusty. The screws are rusted in place. That's going to take some work to get apart.Two other units have screws that just don't want to come out. Not sure if it is rust or if somebody decided to play with thread locker.Of the seven open units, about half have the black caps and half have the blue ones. A bit less than half have the gold plated boards. The rest have tin plated boards.That's all for now..Bob

author: jpb
author_rank: Super Contributor
timestamp: February 05, 2016, 07:29:54 pm
content: Quote from: uncle_bob on February 04, 2016, 12:44:24 amOne of my units I couldn't shift the screws and ended up stripping the head so I had to drill them out.

author: uncle_bob
author_rank: Unknown
timestamp: February 05, 2016, 07:36:34 pm
content: Quote from: jpb on February 05, 2016, 07:29:54 pmHiI got the rusty unit open. It's not all that bad inside. I lost the "outside" board in the process. No big loss there. I still have two other units that I may need to drill. The most interesting thing I noticed was that the Philips head screws at the "bad" locations were head stripped when I got the units. I suspect that somebody at the factory got a little heavy handed.Bob

author: jpb
author_rank: Super Contributor
timestamp: February 05, 2016, 08:13:42 pm
content: I've now finished my 48hour measurement of 7998 against itself to get a noise floor and, considering the crudity of the setup, it is quite good and well below my other measurements which is ok.So here is my final (for the time being) Alan Deviation plots. They are a bit flat, start off lower than expected but then don't drop as much as some other measurements (see for example:http://www.ke5fx.com/rb.htm)Of course, assuming the standards are equal the individual results should be shifted down by LOG10(sqrt(2)) = 0.15 but this is not a big change.What I find interesting is how having a stable reference (7998) gives a much better noise floor than using the internal oscillator in my Agilent 33522A. The mean measured frequency came to exactly 1Hz which was satisfying as well - though perhaps not surprising as I reconstruct the 20nsec clock counts from the measurements on my counter so that they are integer values.Tomorrow I plan to have another go at fixing my broken ones.

author: jpb
author_rank: Super Contributor
timestamp: February 05, 2016, 10:27:33 pm
content: It is not quite the same model but looks close enough to be useful (I don't know if it has already been posted) :http://www.radcomms.net/EFRATOM%20LPRO%20101%20Repair%20Guide.pdf

author: uncle_bob
author_rank: Unknown
timestamp: February 06, 2016, 12:14:16 am
content: Quote from: jpb on February 05, 2016, 10:27:33 pmHiI have a pretty big pile of those as well. It's a *very* different design from Efratom rather than Temex. The common element is that the cell base station guys (Lucent etc) standardized on the Efratom LPRO early on for their internal production of timing modules. When Temex wanted to break in, apparently the "big guys" said - make it the same as an Efratom !!! The result is the gizmos we are all happily hacking away at. It's a Temex LPFRS on a heat sink that mounts on an LPRO footprint. It has a board that converts the LPFRS pinout over to a "close enough" LPRO pinout.Yes that all does sound crazy. Consider that starting in the early 90's the cell guys made up maybe 90% of the Rubidium market. There ar a relatively small number of players in that market. Getting "on board" with one or more of them would have been a really big deal.Just for reference, my LPRO pile came out of Lucent / AT&T base station salvage. I bought them as full (but badly damaged) modules. They were built like a tank so damage to the outside was not the same as damage to the guts.Lots of fun.If you get an LPRO .. . wait for it .... check the caps on the power supply.Bob

author: jpb
author_rank: Super Contributor
timestamp: February 06, 2016, 10:55:55 pm
content: I don't seem to be having much luck (or rather I don't have much skill/experience) with my lot.I changed a couple of crystals which made no difference. Adjusted pots a bit - again to no effect.I decided to swap the working lamp from the water damaged one into the much newer one whose lamp didn't fire (the lamp voltage being down at 0.7V on the serial port output).It was a rather delicate operation - the wires are very brittle and after everything the working lamp no longer worked in the new unit so the lamp wasn't the problem and I damaged the lamp I removed (wire broke off and impossible to solder to what is left).So I now have two units that are probably dead beyond my skills to repair.This leaves me with two working units (one getting towards end of life from the voltage readings over the serial interface) and a mysterious third unit which thinks it is locked but the frequency is far too low. I changed the crystal and this made it worse. I don't know if the lamp fires because I've not run it without the case.The unit with the lamp that doesn't fire does seem to come up to temperature and it produces a good signal on one lamp coil at 135MHz and a much smaller signal on the other end of the coil (?) at 135MHz but only a few tens of mV. Someone else reported higher frequencies for the lamp coil but it may be that my scope probe capacitance is loading things.

author: uncle_bob
author_rank: Unknown
timestamp: February 06, 2016, 11:19:26 pm
content: HiOk, here's what you are looking at:At one end you have a neon bulb that's filled with Rb instead of Ne. Rather than fire it up with high voltage they fire it up with RF. (A neon bulb will fire on RF as well). If the RF end of things does not have enough power (or the bulb is shot) you will get no glow. The RF is running a resonant circuit to increase the field intensity. If that is out of whack, no glow.Once you have a glow, you have a couple of atomic lines being excited. That light goes through another cell that takes out most of what you don't want (nothing is ever perfect). With nothing else in the cell, it would pass through to the photo detector and give you a nice DC voltage on the detector.Toss in another cell (or monkey with the gasses) and you have a bit of magic. Hit the combo with microwaves at just the right frequency and the light to the photo cell goes way down. You have a notch filter. It's a bit nutty because the notch is RF in and light out. The why has to do with quantum mechanics ... we'll skip that for now. The next trick is how to lock to a notch.The normal way to lock to the notch is to modulate the microwave signal and look at how the recovered light responds. Tone in and only tone out = tuned right. Tone in and tone + second harmonic out = tuned wrong. With a bit of work you can create a PLL that will keep things centered up.So what can go wrong:1) No RF into the bulb or frequency way off from correct (= no field).2) One or more bulbs broken3) Photo detector broken or covered in slime4) SRD (or other multiplier) not putting out microwaves5) Cavity not tuned to SRD output (again no field, just at a very different frequency)6) A whole raft of problems in the synthesizer or MCU.7) A copule of other things relating to the quantum mechanics stuff we skipped (C field levels etc)To make it even more exciting:Back in the "good old days" the cells had to be pretty much right on or the (narrow) synthesizers of the day would not lock to the resonance. Along came DSP and DDS and a bunch of FPGA's. Now you do a cheap synthesizer with a much wider range. A greater range of cells can be used (like over 100's of KHz). The magic numbers get stored in an eeprom or flash somewhere and the unit chugs happily on it's way. Does everybody do a Rb that way? Who knows, there certainly are some people who do that.How all this relates to which test points in the LPFRS, no idea beyond what has been posted here. This is not anything I designed. Many of the fine details of how this or that is done vary between manufacturers. The way Temex does it may not be how FE does it or how Efratom once did it or how Symmetricom does it today.edit ... ====================Got a chance to play with 8 of the 10 Rb's today (still need to drill out the other two).5 of the eight lock up properly and appear to be ok.1 of the eight locks up, but it is about 180 Hz low1 of the eight sweeps past 10 MHz without ever locking1 of them starts low and never sweeps as high as 10 MHz, it also has odd voltages.None of this is with any cap changes. No pot tweaks. I simply opened them all up, looked around in them, put a DVM on the 9.2 V supply and let them warm up. I watched them on a 53181. I did not bother to hook up a serial port to them.So here's a question:There are two versions of the CPU board. That has been mentioned before. There is also a version of the RF board that has a daughter board on it. The daughter board has the crystals attached to it. Anybody else seen one? With the daughter board it seems to warm up more like an AT cut based oscillator. The normal parts are quite strange on warmup (very little shift).All for now, more fun in the morning.Bob

author: uncle_bob
author_rank: Unknown
timestamp: February 07, 2016, 05:44:33 pm
content: HiPrevious post is getting a bit heavy with edit adds....I drilled out the other two units. One (this one with the old logo) locks up properly and seems to be fine. The other one starts out way low in frequency and never sweeps to 10 MHz. It goes into a fairly messy jumble of frequencies (all below 10 MHz) after the first sweep or two. I have not pulled the cover off that one yet. No idea if it glows or not.The score card now looks like:Three not working with various symptoms. No two the same problem. No caps changed out yet.One locking, but way low in frequency.The other six seem to be running fine, with no work required on my part. That puts the delivered price of the working units at $56 each. For two day shipping from China, that's a pretty good deal. If any of the others work after repair, all the better.Next step will probably be to swap out caps on all of them and re-check things. I really do not like the look of the ripple on even the units that work fine. Of course if a cap change on the first one has no impact on the ripple, that plan may change.One observation:With or without the heatsink on them, these little guys get mighty hot. At least on a grab it and see basis, they run hotter than the FE's or the Efratom's. For any sort of extended use, some sort of airflow around the LPFRS would be a real good idea. A bigger heatsink might also help. Since the existing heatsink is pretty much non-functional (if you connect directly to the SMA or 9 pin) a new one may not be out of the question.If this has been posted previously, sorry for the dupe.Some Cap voltages:The electrolytic on the RF board nearest the bracket has input voltage on it. (24 V or what ever you use).The other electrolytic on the same board has 16.8V on it.One electrolytic (location varies) on the other board also has 16.8V on it. In both layouts it's the one closer to the flex.The other electrolytic on the MCU board has 9.2V on it.If you are scrounging caps from your junk box, there is no real need for a 35 or 40V part in the 9.2V slot. Aluminum electrolytics do not seem to improve much in reliability once you go below 1/2 rated voltage.Bob

author: jpb
author_rank: Super Contributor
timestamp: February 07, 2016, 05:57:32 pm
content: I thought I'd test the test points on my good unit to compare with my low frequency unit.I scrounged TiN's photos to mark the results (sorry a little scruffy).The major difference I see is the two test points down in the bottom left on the top board (where the physics unit window is). On the good unit these are both at 5V whilst on the bad unit they are at 0V. Otherwise all values seem similiar except the centre of the bottom board where the good unit is around 1.1-1.3V whilst the bad unit is down at 0.63V.The 0V (should be 5V) test points are connected to quad op amps (LM324DG) but I'm not sure what it is doing yet.

author: TurboTom
author_rank: Super Contributor
timestamp: February 07, 2016, 08:38:22 pm
content: I've also got myself a batch of those - yet I decided to go for the other offer without the heat sink. These units anyway run hot and if you cool them externally, only the internal physics package heaters need to run harder. Some cooling may be beneficial but too much won't make things better. So my reasoning to go for the other offer was that these units are equipped with the really crappy "Multicomp" electrolytics which are the probable cause for initial failure which I found true for all of my five units. But -- and this is a big "but" -- they show traces of storage (...or disposal...) under free sky for some time and must have been exposed to moisture - actually they smell like they were pulled from the sewereven though they don't show much moisture stains inside. Yet, they were handled roughly with some deep scratches externally and even some small dents. Two of my units revealed some "rattling" noise inside when carefully shook.I replaced all the AL electrolytics and got all five units to lock correctly. To run any of the oscillators with the original caps (if they are the black multicomp ones) makes no sense and any measurements with those in place are useless - just go ahead and replace them. Yet, I found four of the five of my modules to lose lock if I shake them while they are locked, which may be normal considering the liquid rubidium metal inside may splash around and cause the photo detector to register a "fake dip". The two units that don't rattle and lose lock when shook will lock again quickly (within a second or so) while the two rattling units take much longer or may even not lock at all in certain orientations.Consequenly, I decided to disassemble the physics package of the unit which showed the worst rattling - and found the glass sleeve of the Rb lamp excitation coil to be shattered. The lamp/coil was able to move considerably inside the lamp housing and I consider it a write-off even though a repair might be possible. There's some additional rattling inside the resonator cavity - it seems the Rb cell(s) is / are able to slide fore and aft a little. If this is a real problem, I don't know.Compared to my Efratom LPRO-101, I think the TEMEX units are second choice (design-wise). Considering the questionable condition they are in - probably salvaged from a junk-yard after unprotected storage, they are too expensive (including shipping) and chances to get a really good one are low. So I really cannot recommend to give these offers a go. But that's just my own opinion.Cheers,Thomas

author: uncle_bob
author_rank: Unknown
timestamp: February 07, 2016, 09:10:40 pm
content: Quote from: TurboTom on February 07, 2016, 08:38:22 pmHiIf you dig into the Efratom app notes on their parts, they do a pretty good job going through the details of the MTBF and how it is impacted by base plate temperature. On both the LPRO and the LPFRS, baseplate is the same as one wall of the case. We tend to think in terms of ambient temperature when rating things rather than case temperature. From the Efratom data, you want to keep the case below 50C. That's hot enough to notice, but not hot enough that you can't hold it for a few seconds.Yes indeed I found this silly and ignored it for a while. I spent a lot of time believing that Rb's "just die" after a year or two of operation. Since I started using heat sinks (on exactly the same model Rb's) they seem to run for years and years. All of that leads me to believe that the Efratom information is reasonably accurate.Since the LPFRS seems hotter on the case, I'd bet it needs cooling even more than the LPRO's do.Bob

author: uncle_bob
author_rank: Unknown
timestamp: February 07, 2016, 09:25:23 pm
content: Quote from: jpb on February 07, 2016, 05:57:32 pmHiThere are some open holes in the RF board. They serve as mounting locations for an optional oscillator daughter card. Four of the holes are to the left in the picture, arranged vertically One hole is right next to (to the right of) the middle vertical hole. That hole has the sweep voltage for the VCXO on it. You can (on a bad unit) watch it swing from a bit below 2V to almost 8V pretty much forever and ever.The other holes have about what you would expect. The 16, 10 and 5V supplies, ground, and the 20 MHz VCXO signal. There is a zero ohm jumper that you would *think* comes out when the daughter board goes in ... nope.Bob

author: jpb
author_rank: Super Contributor
timestamp: February 07, 2016, 10:43:03 pm
content: Quote from: uncle_bob on February 07, 2016, 09:25:23 pmThanks for the tip - I think this also connects to one of the test points. On my low frequency one this seems to stay at a constant 1.24V.So it looks as if there is perhaps some sort of voltage scaler/buffer (D2A?) that is failing? The frequency is not being swept - it is stuck at a low value but the software thinks there is a lock.

author: uncle_bob
author_rank: Unknown
timestamp: February 08, 2016, 02:20:02 am
content: Quote from: jpb on February 07, 2016, 10:43:03 pmHiAfter changing out the caps, my unit that used to sweep back and forth past 10 MHz now does not sweep at all. It just sits there a bit below 2 V. My guess is that either I blew something away doing the caps or some of the pots now need to be tweaked. On the other non-functional unit I demonstrated why small diameter stranded wire is not the best thing to use. Gotta go find the Teflon strippers.Bob

author: jpb
author_rank: Super Contributor
timestamp: February 08, 2016, 06:49:46 pm
content: Quote from: uncle_bob on February 08, 2016, 02:20:02 amIt looks like we perhaps have the same problem. It is hard to believe that changing caps will have blown something the same on both boards. I did check all the test points (as per my post above) and the results between the good and bad are very similar though perhaps the bad one has slightly higher voltage on the 125kHz wave forms (the dc-dc converters I presume).The one stand out difference is the output of the buffers (op-amps) on the duff one is more or less zero (a little bit of noise voltage) whilst on the good one it was 5V. But this is a long way from the swept voltage point - in fact it is on the other board I think so I can't see how it is related.The duff one has a very good glow from its lamp so I'd like to get it working - if I do I think it will be a good sample.

author: jpb
author_rank: Super Contributor
timestamp: February 08, 2016, 06:53:27 pm
content: Quote from: TurboTom on February 07, 2016, 08:38:22 pmI think that they have been roughly treated - one of my heatsinks was bent. The advantage of getting the heat sink versions is the heat sinks act as a bit of a shield and provide some protection.I've not tried shaking mine to see if they lose lock - I plan to use them in a lab not on the back of a landrover so I'll treat them quite gently.

author: TheSteve
author_rank: Unknown
timestamp: February 08, 2016, 07:09:21 pm
content: I was going to order another 5 or 10 of these but you guys have talked me out of it. I think I got lucky the first time, they are too expensive to risk more. Any chance the ribbon cable was damaged while you guys swapped the caps?All 5 of mine had the black caps and weren't treated that well but the marks weren't super deep and nothing was bent or water damaged.

author: jpb
author_rank: Super Contributor
timestamp: February 08, 2016, 08:45:15 pm
content: Quote from: TheSteve on February 08, 2016, 07:09:21 pmI wouldn't buy another batch - though I think even with two working ones and a possible third I've probably broken even at an average cost of around £95 each - e-bay prices are quite high at present especially if you add postage and import duty. I certainly wouldn't gamble on buying a single non-working device (some of these no-lock devices seem to go for $200 or at least that is what people ask).It is not that I regret the purchase, it has been educational, but I think probably the early purchasers did well and now the samples are rather worse.I don't think I damaged the ribbon cable - it looks ok but I'll keep an open mind.

author: uncle_bob
author_rank: Unknown
timestamp: February 08, 2016, 08:48:15 pm
content: Quote from: TheSteve on February 08, 2016, 07:09:21 pmHiAnything is possible when you are swapping things around. A stray bit of solder that vaporized right after it blew this or that is quite possible. Soldering parts while watching the Super Bowl may not be the best thing to do. The units have all been opened up and the flex has been "worked" on all of them. The only one that had anything change (AFIK) is the one I swapped caps on. One more variable ... I'm using the 220uf caps. The second one I swapped did not show any difference after the swap.What this *has* stopped me from doing is a fast wholesale replacement of all the electrolytic caps on the boards. Since I have 6 running fine, there is a bit of a risk.Value wise, I'm happy that I got my money's worth. Do I need another 10 right now (to get another 6)? It's not really clear that I *needed* the first 10. I've got ... errr ...umm .... an adequate inventory of Rb's already.Bob

author: TheSteve
author_rank: Unknown
timestamp: February 08, 2016, 09:05:28 pm
content: I worked on one of mine quite a bit with no issues, flexing the ribbon cable a ton. I was always as gentle as possible of course. I used parts with the proper value as you never know when it could make a slight difference with the switching power supply. As I previously mentioned I also used radial instead of axial caps as they are much easier to get. I plan to sell three of mine, keep one and give one to a friend. In the end I will come out ahead financially and still have one to use.

author: uncle_bob
author_rank: Unknown
timestamp: February 09, 2016, 02:41:48 am
content: HiI popped all of mine open and spread the boards apart on all of them. That happened ahead of any testing. Since it also happened on the "good ones", I doubt the flex is the issue. One unit that has a problem also has a crushed in 9 pin connector. That could be an issue, but so far it has not been.Bob

author: BFX
author_rank: Frequent Contributor
timestamp: February 09, 2016, 02:53:54 pm
content: Hi guys,I looking for this unit , can anyone sell me one piece?Ideal from EU (GB, DE).Thx

author: uncle_bob
author_rank: Unknown
timestamp: February 09, 2016, 03:01:57 pm
content: Quote from: BFX on February 09, 2016, 02:53:54 pmHiI'd bet you are looking for a "known good / working / checked out / rebuilt" unit rather than .... errr ... a mechanical sample. Keep in mind that one that works fine for a week, may go nuts three days later. Stuff happens, these have not been gently handled in the Chinese salvage process.I'm not selling any, but I would say that a working unit is worth a bit more than the single piece "parts unit" sells for on eBay ($49). No comment on the shipping cost on the single piece.Bob

author: jpb
author_rank: Super Contributor
timestamp: February 09, 2016, 06:47:53 pm
content: Quote from: BFX on February 09, 2016, 02:53:54 pmMy original plan was to get all 5 working and sell 2 or 3 of them, but as things stand I only have two working ones so I'm hanging onto them for the time being.

author: edavid
author_rank: Super Contributor
timestamp: February 09, 2016, 06:54:55 pm
content: Quote from: BFX on February 09, 2016, 02:53:54 pmThere are some reasonably priced working units on eBay from user "fuzzstik":http://www.ebay.com/sch/Crystals-Oscillators-/7286/m.html?_ssn=fuzzstikI wish someone would buy them, so they would stop tempting me

author: uncle_bob
author_rank: Unknown
timestamp: February 09, 2016, 11:29:44 pm
content: Quote from: edavid on February 09, 2016, 06:54:55 pmHiThe "working" up in big letters and the note way down in the text about "cracked pins that are easily replaced" ... hmmm.I think that (looking at the pictures) they may be as much of a project as the LPRFS is. They may not be, but that's not real clear.Bob

author: edpalmer42
author_rank: Super Contributor
timestamp: February 09, 2016, 11:56:02 pm
content: Quote from: uncle_bob on February 09, 2016, 11:29:44 pmThe pins on the LPRO are a bit unusual. They're actually a set of feed-through capacitors on a small metal plate. If you unscrew the two hex standoffs, you can pull out the plate with the pins and throw it away, as shown in a couple of fuzzstik's pictures. You're left with nice female sockets. So damage to those external pins isn't a big deal. I don't know if it's possible to replace the pins themselves.

author: edavid
author_rank: Super Contributor
timestamp: February 10, 2016, 12:38:33 am
content: Quote from: uncle_bob on February 09, 2016, 11:29:44 pmThey are listed as "used", so you can get a refund if they don't work.

author: uncle_bob
author_rank: Unknown
timestamp: February 15, 2016, 04:37:09 pm
content: HiI got to spend some "quality time" with a good microscope and my collection of LPRFS units. It pretty much confirmed what I had already suspected. I am not the first person to try to repair one of these units. When they came from the factory new, there was no flux on the boards or parts. I can spot several IC's that have been swapped out and flux left on the IC leads.Did this happen at the factory? Did it happen in service? Did it happen after salvage? There is no way at all to be *sure*. I would bet, based on the seller's description that the work was done after salvage. It is rare in a modern factory to see IC's swapped out. Most Telco's do not repair at this level (they swap the entire sub assembly). People who have a 5X price differential between a parts unit and one that is "good working" do indeed take a quick stab at repairs.I have never seen evidence of repairs on my FE's other than the kludge modified units. I also have not seen work done on my Efratom's. The Efratom units never went to China, so that may not mean much at all. Since the FE's and Efratom's came in working, I also have not spent as much time looking at them with a microscope.Bob

author: jpb
author_rank: Super Contributor
timestamp: February 15, 2016, 06:31:32 pm
content: Quote from: uncle_bob on February 15, 2016, 04:37:09 pmA couple of mine had an external wire bodge on the boards (connecting one end of one of the electrolytic capacitor to a nearby resistor), but it was identical on two boards and looked like it might have been a fix for early board models rather than a repair.

author: TheSteve
author_rank: Unknown
timestamp: February 15, 2016, 06:35:07 pm
content: Quote from: jpb on February 15, 2016, 06:31:32 pmI had the wire as well, it was white. I am sure it was installed when manufactured.

author: shempe
author_rank: Contributor
timestamp: February 15, 2016, 06:36:10 pm
content: Yep same bodge wire here. on a few.

author: uncle_bob
author_rank: Unknown
timestamp: February 15, 2016, 06:41:16 pm
content: HiI have a few examples of the white wire as well. It was well done and properly cleaned after the fact. The replaced IC's I've found and other components ... not so much. I can indeed believe that a test select component might be a flux monster. That sort of thing might be done by a tech who isn't very careful .... (or by some guy named Bob ..). On the replaced IC's, I just don't think that is what happened. That sort of work would go to a repair station and be done properly. If they do the wire right, they do the repairs right ....Bob (the guy with the giant flux bottle ...)

author: TheSteve
author_rank: Unknown
timestamp: April 12, 2016, 06:00:59 am
content: I finally found a box I really like to mount one of these Rb standards in. It is a Hammond # 1455NHD1601. I would have preferred the black version but I only came across a good deal on the clear anodized. The BNC jack is mounted such that 4 more can be added in the future. I am pondering adding a buffered version of the internal 5,10 and 20 MHz square wave signals as well as a generated 1 PPS. I used a single dual color LED with a common cathode for status indication. The only change to the Rb itself was the addition of a 1K resistor in parallel with the lock signal 2.2 K resistor to brighten up the red LED. The 2.1mm input power jack has a polarity protection diode and a few capacitors for noise filtering. I am using a 24 VDC @ 2.7 amp laptop style switching power supply for power. The Rb heatsink is bolted to the box on the bottom. The top has an extra piece of aluminum bar stock added which is a wedge fit between the top of the Rb standard and the top cover for better heat transfer.

author: TiN
author_rank: Super Contributor
timestamp: April 12, 2016, 10:54:23 am
content: Nice box, I bought some too, hoping to integrate Rb+GPSDO+RPI with OLED 16x2 (which did not work on Keithley 2304) together and make Stratum-1 box/referenceOnly issue to find time to do all that.

author: uncle_bob
author_rank: Unknown
timestamp: April 12, 2016, 11:39:08 am
content: Quote from: TheSteve on April 12, 2016, 06:00:59 amHiThe heatsink on these gizmos was designed for high air flow. They run hotter sitting on the bench than most of the other telecom Rb's. That's not a scientific observation, just what I notice picking them up after they have been running. I would strongly recommend getting a fan into any enclosure you use for one of these. The failure rate goes up quickly as they get hotter. You really want to keep the case under 40C.I've killed a lot of surplus Rb's over the years by ignoring this point. Fans are really easy to talk yourself out of. They are noisy, they cost money, they are hard to mount, they pack dust in to things. M100's die when they get hot. FRK's die when they get hot. LPRO's die when they get hot. FE5680's die when they get hot. All of those live a good long time if you keep them cool. SR10's die weather they are hot or not.Bob

author: TheSteve
author_rank: Unknown
timestamp: April 12, 2016, 04:37:49 pm
content: I suppose in the telecom market fans are very common, as is loud equipment. In my home lab I have no interest in extra fans. I think I'd rather have the Rb unit die. It would be nice if they would build them a little bigger with the PCB insulated from the Rb cell/heater but I know they are building for a target size or rack thickness etc. I will thermal probe the unit when I have time but I believe the heatsinking on the box is enough to keep the unit well within the Temex published spec's. Of course it probably still cooks itself at those temps. Either way if it only lasts a few years that is fine, it owes me nothing and the caps are easy to replace.

author: uncle_bob
author_rank: Unknown
timestamp: April 13, 2016, 12:47:53 am
content: Quote from: TheSteve on April 12, 2016, 04:37:49 pmHiFor a "no fan" structure, you get to a heatsink that is roughly 10" x 10" x 2". They aren't terribly expensive, but they are pretty big. That size assumes you have it vertical. The horizontal version is a bit bigger. A fairly small heatsink will do trick combined with a fan that is in the 19 dba range. If you can hear that on your bench ... you have a very unusual bench.Bob

author: Rémi
author_rank: Regular Contributor
timestamp: January 24, 2017, 08:44:07 am
content: I bought two units and received them yesterday. I've ordered new electrolytic capacitors to replace the old ones.I bought these capacitors on Ebay, Philips 123 47uF 35V 125°C Axial :http://www.ebay.com/itm/122322378097?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AITLet's see if the units work when the capacitors are changed.

author: CJay
author_rank: Super Contributor
timestamp: January 24, 2017, 12:34:26 pm
content: Quote from: Rémi on January 24, 2017, 08:44:07 amInteresting, was that from an eBay sale or somewhere else?Out of curiosity, if anyone here in the UK has some of the original batch still knocking about on a shelf I might be interested in some on working ones?

author: Rémi
author_rank: Regular Contributor
timestamp: January 24, 2017, 12:39:28 pm
content: Quote from: CJay on January 24, 2017, 12:34:26 pmYes it was from an eBay sale, the same seller as TiN and other members have bought their units from. His username is yixunhk (http://www.ebay.com/usr/yixunhk?_trksid=p2047675.l2559). Unfortunately I think that I bought the two last units.

author: Orange
author_rank: Frequent Contributor
timestamp: January 24, 2017, 04:18:38 pm
content: Quote from: Rémi on January 24, 2017, 08:44:07 amThose capacitors you bought might be bad as well. Philips stopped making them in 1999, their caps business was sold to Beyschlag Centralab componentsAKA BCcomponentshttp://www.vishay.com/company/brands/bccomponents/

author: texaspyro
author_rank: Super Contributor
timestamp: December 05, 2017, 04:48:27 am
content: I recently bought a Spectratime SRO100 Rb. Very small, 11-19V, can discipline itself to 1 PPS input. I have Lady Heather working with it. It seems to be a very nice and capable Rb.I noticed that the LPFRS serial commands are very much like some of the SRO100 commands, so have also added support to Lady Heather for the LPFRS. I just ordered an LPFRS to test that code.I also did an adapter board to connect the SRO100 to my X72 signal breakout board (breaks out the signals to 5 BNC's and has a true RS-232 port). I will probably also do a adapter board for the LPFRS.

author: texaspyro
author_rank: Super Contributor
timestamp: January 13, 2018, 01:56:11 am
content: Quote from: texaspyro on December 05, 2017, 04:48:27 amI have Lady Heather working with the LPFRS. Attached is a plot of the LPFRS powering up.The LPFRS adapter board for my X72 BNC board will have a PICDIV chip for generating a 1PPS output. The adapter board should also work with the LPRO (but the LPRO has no serial port).All the screws on my LPFRS heatsink were chowdered to hell and loctite'd in. I had to use a dremel to turn them into slotted screws. Some required a little torch work to get them loose... grrrrr.

author: texaspyro
author_rank: Super Contributor
timestamp: January 13, 2018, 02:03:47 am
content: Oh, and here is an ADEV plot of the LPFRS output done with a TAPR TICC clocked by an HP-5071 cesium oscillator. The unit was off -0.003 Hz. I used the frequency setting commands to get it on freq.