Standford Research DS345 Error - Page 1
Forum section: electronics / repair

author: bostonman
author_rank: Super Contributor
timestamp: September 03, 2020, 01:25:58 am
content: Does anyone have a service manual for the DS345 function generator?Mine began displaying (what looks like): Offset 0 ErrorSee picture for the exact displayI looked in the manual, and it states it could be a offset control or output amplifier, but I don't know where these circuits are located.

author: bostonman
author_rank: Super Contributor
timestamp: September 03, 2020, 01:45:45 am
content: I found a manual that included the schematics.

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: February 02, 2022, 05:55:33 pm
content: Mine has the same error displayed. Did you find anything?Thanks in advance.

author: fzabkar
author_rank: Super Contributor
timestamp: February 02, 2022, 09:01:51 pm
content: SRS DS345 SYNTHESIZED 1UHZ-32MHZ FUNCTION 10MHZ ARBITRARY GENERATOR (Meter: Service Manual 157 pages):https://elektrotanya.com/srs_ds345_synthesized_1uhz-32mhz_function_10mhz_arbitrary_generator_sm.pdf/download.htmlSTANFORD RESEARCH SYSTEMS DS345 SYNTHESIZED FUNCTION GENERATOR 1989 (Meter: Service Manual 139 pages):https://elektrotanya.com/stanford_research_systems_ds345_synthesized_function_generator_1989_sm.pdf/download.html

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: February 02, 2022, 10:29:41 pm
content: Thanks! Already have that though...

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: February 02, 2022, 10:48:09 pm
content: Like this...Maybe someone else has seen it. Two already here so far.

author: bostonman
author_rank: Super Contributor
timestamp: February 03, 2022, 02:45:29 am
content: QuoteUnfortunately I've been trying to finish other projects and haven't had a chance to re-address this.

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: February 03, 2022, 03:23:25 am
content: Ok... well if I find the problem then, i will post about it.Thanks for responding.

author: bostonman
author_rank: Super Contributor
timestamp: February 03, 2022, 03:32:51 am
content: I also have a DS340 with a RAM issue I think.I pulled both of these off the shelf and got errors on both which was somewhat annoying.From what I read regarding the DS345, it has something to do with checking the voltage out of an amplifier. Unfortunately I didn't get back to these because I needed them to repair something else requiring I use these, however, when these didn't work, I resorted to another piece of equipment, and I'm still working on the other item.

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: February 03, 2022, 03:24:34 pm
content: Since the error description mentions the main amplifier output, and that eventually connects (through the attenuator) to the outside world, I find that likely to be where the problem lies. Particularly if someone put a signal INTO that jack that had a large DC component, or high signal level. Stranger things have happened.I don't see much in the way of protection that could stop damage if that were to occur.I should receive the item tomorrow for a first look.

author: bostonman
author_rank: Super Contributor
timestamp: February 03, 2022, 03:26:17 pm
content: I'm uncertain how deep you've dug, but the error message is listed in the manual and it points to some possibilities.

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: February 03, 2022, 03:58:04 pm
content: As I mentioned I should have the unit in hand tomorrow. So far just looked over the schematics and descriptions in the manual. The connectors for the outside world are always susceptible to the errors of humans. We will see if that is the case soon... Please standby.

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: February 05, 2022, 12:47:19 am
content: This may well be one of those repair attempts that comes back to bite me in the behind...I received the item and it booted to the error displayed as above. Measured the offset at the output BNC (floating) and it had -4.8 volts DC on it. Opened it up and started probing at the output amp and it was consistent with the -4.8 Volts. Continued back to the input of the differential to single ended amp. Everything seemed consistent with that offset, then, suddenly it all seemed to go back to near zero offset. Re-booted it, and Voila' NO error message!!!So now the question is WHY? I did briefly turn one or two of the 20 turn pots slightly back/forth, but I am doubtful about that being the issue. I then noticed that the DC Offset was not meeting spec, so decided to try running Autocal. Once I figured out how to enable it (can't find in manual) and ran the routine, it now checks within spec. I will be suspicious about this until it fails again.

author: mawyatt
author_rank: Super Contributor
timestamp: February 05, 2022, 03:29:10 am
content: Long ago we had a few of these SR Waveform generators, they were really nice and worked quite well I recall.Suspect that what may have happened is the pot wiper had disengaged or made a high resistance contact, and your turning it wiped the surface clean and made good contact.Anyway, good news is you have a really nice waveform generatorBest,

author: bostonman
author_rank: Super Contributor
timestamp: February 07, 2022, 03:05:30 am
content: Thanks for the update.I have several projects I'm working on, but I'll make a note of this. Maybe I'll spend a few minutes this week removing the cover and taking similar steps.

author: bostonman
author_rank: Super Contributor
timestamp: February 09, 2022, 12:48:49 am
content: QuoteI am curious if you remember what the amplitude setting was on the front panel. Tonight I measured the DC voltage at the BNC and it too was negative, but about -2.x when the amplitude was 1V RMS. When I set it to 2V RMS, it went to about -4.6V.I need to look at the schematic again, however, I'm wondering if we had the same problem due to the amplitude setting.

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: February 09, 2022, 02:49:21 pm
content: The short answer is no. I don't remember the setting. Now that you have mentioned it though, it seems to me that it may have started working again after I changed the DC offset setting.Mine has more problems. Someone manhandled one the two adjustable chokes in the oscillator. L203 I think it was, the one for F adjust. not the AGC. Anyway the slug is still intact, but the threaded plastic seems to be stripped out. These chokes are no longer made. I did find some on ebay though. Working on this board with the super tiny traces and vias is a real nightmare.

author: bostonman
author_rank: Super Contributor
timestamp: February 09, 2022, 02:56:19 pm
content: That sucks. Do you need me to take pictures of mine to help with your repair?I assume you don't have a microscope?I attempted to change the amplitude (and frequency), but I didn't try changing any other settings on the front panel; but will try tonight. Everything looked like it was set to zero though when I ran through the output settings, but maybe exercising offset voltage will allow something to fall into place.

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: February 09, 2022, 06:09:36 pm
content: Thank you for the offer. I don't think that will help. I guess hot air is going to be the way to get this Choke can off the board with the least destruction. I do have a headset Lens that works well, just need to get close up. My eyes ain't that good anymore though.

author: bostonman
author_rank: Super Contributor
timestamp: February 09, 2022, 07:29:32 pm
content: Where are you? I assume not Boston area?

author: bostonman
author_rank: Super Contributor
timestamp: February 10, 2022, 05:07:26 am
content: I messed around with the output offset setting on the front.Moving it between both extremes (negative and positive), the output at the BNC connector went from around -4.4V DC to -9.4V DC.The relay was clicking as I moved the offset voltage and thought maybe the relay wasn't working correctly. Once years ago I had a power supply where the relay stuck and tapping it (or maybe just exercising) fixed it, so thought maybe exercising the relay a bit would solve the issue.Unfortunately this didn't seem to help.

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: February 10, 2022, 03:59:17 pm
content: Hi,No, not Boston, Central California Coast.Your DC offset measurements are off for sure. Should be +/- 5V P-P. Did you try running AutoCal? If so, does it give you any error messages? Sounds like an issue in the Output Diff to single ended amp.I was lucky to find a spot on L204 where the slug stopped moving around, and it calibrated out very good. 2980 is the starting point for the CAL DAC value for circuit adjustment for the oscillator, then the actual DAC value is set after the circuit adjustments. It's not too far off about 3130 or so, and the 40Mhz osc runs about .6Hz off at the 10MHz out jack, dependending on room temp. I'm not changing out L204 unless there are further problems. Too many chances of something going wrong changing that part.There is a Test Point J217 to set the AGC voltage closest to zero (manual does not say any exact value)I am getting around -9.4 or so there. If you are inside yours if you could give me that voltage reading it could be handy. There is a red Test Point on both sides of the top PCBA near the edge of the board in the osc ckt. Thanks in advance.

author: bostonman
author_rank: Super Contributor
timestamp: February 11, 2022, 04:34:59 am
content: QuoteI can take care of it this weekend, but do you trust the voltage readings on my unit that has an error? If you do, would you mind taking a picture and circling which test point(s) you want me to measure just to confirm I'm measuring the correct points?

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: February 11, 2022, 04:53:53 pm
content: Hi,I just need a sanity check on that AGC test point J217. another ckt. unlikely to affect it.Here's a view of the component side of the board from the manual.Thanks in advance!

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: February 13, 2022, 02:54:29 pm
content: Suddenly, there are much bigger problems... I powered it on after days of it working correctly, and during self test it now displays offset 9 error.The manual says all possible errors are listed, but no mention of this error. So trying to figure out a troubleshooting plan. First up, measure all the supplies for correct voltage and ripple.

author: bostonman
author_rank: Super Contributor
timestamp: February 13, 2022, 03:02:25 pm
content: This is unfortunate.Silly question, are you sure it's actually 9? I feel the designers didn't do a good job making the errors legible because deciphering mine took a few minutes.The designers should have just used whole incremental numbers instead of trying to display words on an LCD display.

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: February 13, 2022, 03:31:31 pm
content: I hear what you're saying... it should have been error 0 through error xxx. It sure looks like a 9 to me. The confusing part is they say all possible errors are listed in the manual.Obviously others can be generated.

author: bostonman
author_rank: Super Contributor
timestamp: February 13, 2022, 03:36:34 pm
content: Can it be this:Offset O Err 9 Output has excessive DC offset when set to 0 (>±100mV). Can be a problemwith offset control or output amplifier.This is on page 76 (assuming you have the same revision PDF manual I have).Maybe the O is really a space holder for the 9?

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: February 13, 2022, 03:47:34 pm
content: Thanks to you I took another look. They also mix uppercase and lower case letters which adds even more confusion. There is a self test error in the manual...Shown as...Offset G Error 9 The DC offset function gain is more than ±10% from nominal. Can be aproblem with DAC or output amplifier.See how it is showing uppercase G ? Well the display is actually showing a lower case g... which also really looks like a 9.So I'm going with g.

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: February 13, 2022, 03:51:26 pm
content: Disregard the 9 I put in from the manual... that is only the response code when using commands from GPIB. (also confusing)

author: bostonman
author_rank: Super Contributor
timestamp: February 13, 2022, 03:53:25 pm
content: Too funny, I actually just saw that G error message in the manual and realized maybe I was wrong to assume O was a place holder, but didn't think to consider little g versus capital G.You posted the reply just before I had time to gather my thoughts and post an update.The funny thing: the programmers must have went through an extensive amount of effort to display an actual 'word' on the screen. I can see if they didn't have intentions of creating a manual with a list of error codes, so they they tried making it an obvious error to the user, but they listed all error codes in the manual.It would have saved lots of time just having (as you stated) error 1 - xxx.

author: bostonman
author_rank: Super Contributor
timestamp: February 13, 2022, 03:57:14 pm
content: QuoteBy the way, I appreciate the compliment. Many on this site have helped me, and, when I see posts by others on questions I can possibly help with, they already have numerous responses.So it's nice to see that my contribution made a difference.

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: February 13, 2022, 03:59:30 pm
content: Yes, you prompted me to delve deeper into this and we both agree the error codes are a source of much confusion!!!

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: February 13, 2022, 04:06:34 pm
content: The programmers in their quest to simplify for the user, complicated it instead!

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: February 13, 2022, 04:13:01 pm
content: So my original error, and your existing error as shown in the manual is...Offset O Err Output has excessive DC offset when set to 0 (>±100mV). Can be a problemwith offset control or output amplifier.Shows the uppercase O (for output?) but shows it on the display as lowercase o. Originally I thought it was a Zero being displayed!!!

author: bostonman
author_rank: Super Contributor
timestamp: February 13, 2022, 04:13:35 pm
content: I'll admit, I'm happy the manual has the error code list and schematics. I'll take having to figure out the hieroglyphics over not having access to such material.I just can't imagine the additional programming time and time to think of a 'word' to display on the screen that went into the code list. Not to mention others on the project approved such craziness.

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: February 13, 2022, 04:18:10 pm
content: CERTAINLY! The crazy thing too, they did it all for the USER!

author: bostonman
author_rank: Super Contributor
timestamp: February 13, 2022, 04:25:10 pm
content: I think it was for job security so the software engineer(s) could have a job for life and everyone need to ask him/her for assistance with interpreting error codes.Although, a decoder wheel could have been used where 9 = g, o = O, I = 1, oh, and maybe you need to hold the unit in front of the mirror upside down for other, more complex error codes.

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: February 13, 2022, 04:27:58 pm
content: Ah... you're on to something now!My plan is back to poking in the output amp where the original error was generated. Hopefully it doesn't just start working again like last time.

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: February 13, 2022, 04:37:31 pm
content: I wonder if SRS still has it's User Friendly Programming Dept. ? They produce so few new products it's surprising they are still around at all. They are just over the hiil from me in Sunnyvale, CA. (Silicon Valley)

author: bostonman
author_rank: Super Contributor
timestamp: February 13, 2022, 04:46:53 pm
content: Not to deviate away from the main topic in this thread (as I tend to get frustrated when I'm reading through a thread that is on key to an issue I'm trying to fix and it suddenly takes a sharp left), but I am big into the Commodore 64 and see old software company advertisements in PDFs and wonder what occupies that space now where such a large company once resided.In some cases the building appears to be present (using Google maps), but it's amazing how many companies come and go. Relatively recent I came across a company in MA when browsing an old C64 magazine; or I'll see people who wrote into magazines who are MA based. You have to wonder where those people are now and/or if they realize they can obtain (in PDF) the question they wrote to a magazine as a kid.Hopefully the problem with your SRS doesn't vanish again because it can be frustrating when you want to use that for testing and have to hold your breath on whether it will work (or is producing an accurate output).

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: February 13, 2022, 04:53:09 pm
content: One source I use sometimes in desperation is the wayback machinehttps://archive.org/web/web.phpfor information on the past. Not always 100% on everything, but a good resource.The other possibility of course is it will revert back to the error you are seeing, (my original error).

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: March 02, 2022, 04:16:43 pm
content: So without boring detail, but after many hours of troubleshooting, replacement of suspect ICs (put on sockets), and resoldering many areas (specifically the output diff to SE amp), the unit now passes all tests, and the AutoCal procedure. It also seems to meet specs.However, I do not trust it, and fully expect something will pop up again, although it has been running trouble free for several days now. No idea exactly what I did that actually got it to this point. More luck, than skill.

author: bostonman
author_rank: Super Contributor
timestamp: March 03, 2022, 12:31:55 am
content: I know you're not comfortable with the "repair", but hopefully this is good news and it remains working.Most likely you would have been happier seeing something wrong like a cold solder joint or a bad component.Unfortunately I haven't returned to analyzing mine yet due to my soldering iron breaking. Thankfully I have a junk iron that somewhat handles the components on the Weller PCB. Hopefully I can get my iron repaired soon because, as you know, without an iron, all repair projects get placed on the back burner.

author: bostonman
author_rank: Super Contributor
timestamp: July 23, 2022, 04:06:27 pm
content: I'm resurrecting an old thread as I've been working on my broken unit with a 'Offset 0 error code'.I'm measuring U600 and getting 5.6v on pin 2, 5.4v on pin 3, and the output is pegged at -12.5v.Obviously pins 2 and 3 should be almost equal which is why the output is pegged. From what I can tell, it looks like I need to trace OUT_OFF (label on the schematic on page 147), but I haven't located it.Has anyone worked on this section of the circuit, and has anyone traced the OUT_OFF label to the connecting point?

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: July 25, 2022, 05:11:54 pm
content: Unfortunately there are quite a few reasons why U600 gets an undesirable offset DC. This is exactly where I have been spending time looking at all the possible ways. If you want to look at one, OUT_OFF, that's the actual voltage you can punch in at the front panel for offsets you desire. That comes from the top board at U107A pin1, via pin 25 on the 60 pin cable (look at ckt. page DDS ribbon, a/d's and d/a's for System) but it is not labeled at all on that page! So, then, you have to go to ckt. page DDS Ribbon Cable, Trig, and Sync Select, to see the other end of the cable at JP401 pin 25 and THEN you will see it marked!Not sure of your unit, but mine is quite early on, and they (SRS) made a lot of changes to the boards, and do not document anything or give boards any Rev numbers. The only way I discovered this was from purchasing a couple other units with later S/N's to help TS this beast.In my case I found a few things, and blew up a few things in the output amp along the way. All those were cleared up. what I am left with is probably why they made some changes in the ckt. that drives U600. Oh, and by the way... SRS has given us two U600s in this unit!!! the other is the AD834 on ckt. page DDS Filters and Doubler. But, my issue seems to be the Gain Adjust ckt. that precedes Doubler AD834 U702 on ckt. page DDS Sync and Gain Adjust. There are two signals here. One is the main function Gen Signal, the other, DC, in Gain Adjust. Combined up in the AD834, then sent through two 50 ohm coax to the lower board amp into U600. You'll see a red arrow for the DC levels. My issue seems to be DC DRIFT over time... a LONG time. Days. But eventually causes enough offset to give errors in self test. This seems to be where they made board changes before the AD834 in the DC Gain ckt., using different op amps than shown in the schematic. I'm not convinced it is worth modding the board to match the later ones. The curious thing is they did not change IC's, they just re-routed traces to use different ICs.Hope this might save you time. Check your S/N, and compare with other photos of units on Ebay.I did find a way to reset this offset, and it will again last for days on end, and eventually trip with errors again. The AD834s are kind of strange with this. Maybe there is a fix for it.

author: bostonman
author_rank: Super Contributor
timestamp: July 26, 2022, 03:00:37 am
content: After posting about trying to locate where OUT_OFF is on the schematic, I manually traced the circuit and discovered it goes to pin 1 and then got confirmation from you.I must have spent two-hours looking at the schematic trying to trace OUT_OFF and can't believe it's not on the schematic You're also correct, there are two U600 chips which threw me off for a bit.From what I can tell, and comparing to a good one, it looks like U600, pin 3, is the culprit causing the output of the OP-AMP to go to the rail. It's my opinion the board is built well and a cold solder joint wouldn't be the issue. I tried removing the square chip in the socket and cleaning it just in case corrosion is causing an open connection, I applied pressure on the ribbon cable for the same reason (and cleaned it), but can't find anything related to a bad connection.A thought I had was to remove the battery. Maybe this would cause a hard reset. Have you tried this?

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: July 26, 2022, 03:46:44 pm
content: Hi,I don't believe it is a bad connection problem. Nothing leads me (in my unit) to that conclusion. Yours may be different.Well, changing the battery for a new one might be good (it's old for sure), but somehow doubt that will resolve any offset problems. I think the recall-able factory CAL settings are stored in a non-volatile memory, so battery swaps only destroy user settings. Pretty sure. It will be interesting if you try it to know the results. May as well put a new battery in at the same time if you do it.One thing I tried is diconnecting, and isolating U600 pin 6 from the transistor buffers on the output. Check to see if the trace has zero volts, or close to that, and put zero volts on the trace if it's close. Those 2n3904, and 2n3906 transistors blow easily, and short, check them. Also, one of the traces there is extremely close to the transistor pin pad holes. Then look at those inputs on pin2, and pin3 again. U600 is pretty hardy, not seeing issues with it. The output amp should also have close to zero DC offset now.Ultimately (in my case), the real issue causing offset was not U600 circuit, or the output amp, but the offset coming from U702 AD834 over the coax from the upper board. The open collector outputs on it, require a bias voltage higher than it's main supply bias. That voltage comes from the lower board in the output amp over the two coax. R615, and R616 supply the voltage from U602 6.8V Reg. to U702 AD834 collector outputs. I found that lowering that voltage on either collector output (at the coax) with a resistor to ground of about 600 ohms, and then removing it, would reset the offsets, and then all good for days on end. Ultimately creeping back again, only to trip into error once more.I also swapped out several op amps, and U100 bi-lateral switch in that OUT_OFF circuit to no avail. Also suspecting, but never changing the D/A converter U109 in that ckt. Very expensive, obsolete, and ebay only replacements.Good luck in your TS efforts!

author: bostonman
author_rank: Super Contributor
timestamp: July 27, 2022, 01:17:03 am
content: I have a SRS DS344 (?) that doesn't have a reference. That has a dead battery (it measures about 0.3v) and gives an error on power up, but then doesn't return providing I keep AC plugged in during reboots. This should just be a battery issue.While I was at it, I measured the voltage in my bad DS345, and it was fine. The battery isn't very expensive, but it's not cheap either. I may hold off buying a replacement battery since I don't really use the non-referenced version often; nor is the error an issue since I can re-power it.As for the bad DS345, I'm uncertain how much more time I'll devote to it. Unfortunately I have many projects that have popped up lately and lingering ones. Last week I was looking at my equipment trying to figure out which ones were broken, and, since I dislike keeping broken stuff, thought to give it another look in hopes the error went away or a simple wiggle of something would fix it. I even tried moving the little pots one way and then back into the same position hoping they were dirty. With the exception of the other unit with a dead battery, this is my only piece of test equipment that remains broken.

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: July 27, 2022, 02:28:27 pm
content: We all hope for, and look for the easy fix, but sometimes it does not happen. This has been one of, if not the most, challenging pieces of equipment I have troubleshot. The more challenging a problem is, the more you stand to learn. It is of course necessary to weigh the worth of your time, vs. the worth of what you may learn, and of course the dollar value of the equipment as well. I have not given up yet, but I may set aside, and go back to it again. Sometimes that helps too. Brain refresh.

author: bostonman
author_rank: Super Contributor
timestamp: July 28, 2022, 02:39:53 am
content: I find some of these failures are so common that it's not worth reinventing the wheel which is why I sometimes ask. Most times I like troubleshooting myself, but it usually leads me to a few questions about components which is how I learn as I troubleshoot. I've learned quite a bit from this site just from posting questions about individual components as I troubleshoot.As for the DS345, I find their reference designation labeling horrible. I didn't get too involved in the labeling, but the numbering doesn't seem to follow a standard flow. I think the board on top was designed later by someone else who didn't know U600 was already used elsewhere.QuoteThis is the point I was making about not having time to work on this. If I had to guess, as previously mentioned, I don't sense it's a bad solder joint because the board looks too good. From the cleaning I did, I believe a dirty ribbon cable connection also isn't the problem. Because this is some sort of feedback loop circuit, I sense something is wrong on a digital circuit probably in the LSB end. I compared a good unit, and the DAC (U109B) output seems good, but if a LSB wasn't working correctly, it would probably cause the wrong voltage which would get fed back in the loop circuit.Another thing I thought was odd: the 15 and -15 is around 13.6V I believe. I thought maybe this was an issue, but seems the same voltage on the good one.Personally, I suck at flipping from page to page to follow schematics (and technical books for that matter) in PDF form. I considered extracting all the schematics and having them printed on C size paper at Staples, but not sure I want to devote the money and time to troubleshooting this at the moment.

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: July 28, 2022, 02:53:37 am
content: I totally get what you are saying. This is not an easy unit to troubleshoot at all. I agree with all the complaints you mention. Two U600s is just not acceptable.Not sure if I have EVER seen that on any set of schematics before. No, I have not. However, when the unit works, it is great, no complaints, and good specs... well, except maybe the uppercase lowercase display junk. I wonder if SRS will even quote a repair on these... more likely want to sell you a new one.

author: bostonman
author_rank: Super Contributor
timestamp: July 28, 2022, 03:01:35 am
content: Having worked in repair for many years, I'd be willing to bet someone who works or worked at SRS knows exactly what is wrong with these units.In all my years, it was rare we ever had a one-off failure.Having said this, it's a tease that someone knows how to fix this and yet, we are stuck with a broken unit.You're correct, they are nice when they work. I wonder if a logic analyzer on some of the digital lines would help see what is going on.

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: July 28, 2022, 03:22:33 am
content: Possibly, but I think (at least in my case) there is an analog DC voltage offset creeping up, or down, in one of the many op amps, or the AD834 Doubler just before U601 is actually bad. Anyone??? Bueller???

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: July 28, 2022, 03:34:05 am
content: Sorry meant U600 in the Output amp section. Not the other one that's another AD834 Doubler.

author: bostonman
author_rank: Super Contributor
timestamp: July 29, 2022, 02:13:36 pm
content: I was thinking yesterday, maybe searching on LinkedIn for a SRS employee may lead to someone who works in repair.I don't have a LinkedIn account, nor am I sure if it's possible to search by company, but thought to throw that out there.

author: bostonman
author_rank: Super Contributor
timestamp: July 31, 2022, 12:53:53 am
content: I found an interesting problem. I put a logic analyzer on U100 of the good SRS and it failed power on test 100% of the time. Sometimes it gave the same Offset 0 Err as my broken one, sometimes Offset g Err.I had leads on pins 3,6,9-15 using a IC clip. Once I removed ONE logic analyzer lead from pin 13, it booted fine. Gently placed the wire on the IC clip pin, and it failed boot, off, passed, on and failed. I thought the IC clip was shorting pins, but I proved that wrong because all it took was the impedance of the wire to fail boot.Also, i pulled the positive side of the battery to ground to reset the RAM and that didn’t solve anything.In a precision post I said the 15 is 13.5, but realized I need to use circuit ground and not chassis.On another note, U107 pins 1,2, and 3 should have +107mV on pin 1, and +49mV on 2 and 3. The broken SRS only has -11mV, -5mV, and -4mV respectively.

author: bostonman
author_rank: Super Contributor
timestamp: August 01, 2022, 01:16:45 am
content: Sorry, I typed that last update on my phone and noticed I made a few errors.Shorting the battery was done on my bad SRS in an attempt to reset memory as previously and briefly discussed.I also typed 'in a precision post'. I meant: in a previous post

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: August 01, 2022, 04:36:39 pm
content: Sounds eerily like you are re-tracing my troubleshooting efforts. As mentioned earlier replaced U100, U110,U107, all to no avail. Eventually led to the collector outputs on AD834 (U702) drifting (these are Current outputs so difficult to check as voltages). These lines are pulled up to over 6 volts roughly by resistors R615, and R616 (57.6 ohms each), in the Output Amp., and driving the inputs (2,3) of U600 in the power amp ckt. Really hard to check the currents driving the input of U600, and if you can actually see voltage levels unmatched there at pins2, and 3, you know there are large differences in current, as well. Are you able to actually enter user offset voltages using the keypads, or no? Any changes seen at U600 if you do so?

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: August 02, 2022, 12:29:50 am
content: Shorting a lithium battery is not recommended, or one of the best ideas... probably much safer taking it out of ckt.https://industrial.panasonic.com/cdbs/www-data/pdf/AAA4000/ast-ind-183090.pdf

author: bostonman
author_rank: Super Contributor
timestamp: August 03, 2022, 06:16:14 pm
content: QuoteSorry for not responding sooner as things have been hectic.I haven't messed with the offset settings while measuring anything. I don't want to bail on this issue, but, as you stated earlier, you can only go so far sometimes before you need to work on other projects.Unfortunately I can't even do any soldering because my Weller is broken (I have a thread on this already), and it looks unrepairable because I've tried everything several times over leaving me without the ability to solder and a hefty bill to get a new (decent) iron.Thinking out loud for a moment, and also with less experience in trying to repair this unit than you, U600 isn't getting fed a voltage that's far off one end leading me to believe (as I mentioned) a LSB isn't working correctly. I don't have the schematics in front of me to see which components you changed (I'll look later), but I think we can almost rule out a component that would cause a severe voltage difference. Since it's a feedback circuit (or I believe it is), I'd think a noisy internal oscillator, oscillator that has drifted out of spec, a bad capacitor, or a DAC/ADC that has a bad LSB.

author: bostonman
author_rank: Super Contributor
timestamp: August 04, 2022, 02:28:55 am
content: I have been looking at the schematic and the components you replaced.There is something I question about this design that baffled me last week. U100 gets the output channels selected by the ABC lines and Enable line. If the output is switching between which one of the five op-amps is fed voltage, how are the outputs of the op-amps not jumping due to momentarily having zero volts on the input?As an example, the input of U107A will go low for a short time causing the output to hit the rail momentarily. There must be some capacitor holding the voltage for that moment.I'm thinking U203 has drifted causing clocking issues. I don't see another oscillator, so this is what leads me to this one. Let me know if you've seen other oscillators.Let me know what you think because what I could try: connecting a frequency counter to the output of U209D referenced to an atomic clock. I can compare it to a good unit too.

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: August 04, 2022, 03:33:59 pm
content: U203 according to the Schematic is the optional ovenized oscillator (OVEN_OSC), and is not part of the standard unit.Even with that option, it only provides a correcting sync signal to the main oscillator X200 at the varactor diodes from U206, as does the external timebase as well... Does yours have that option? None of mine do. If yours has it, disconnect it. Is it fixed now? Doubt it.Or put your GPSDO into external oscillator. Fixed now? Probably not.But... according to the Parts List, U203 is a SN74HCT373 Octal Transparent D-Type Latches With 3-State Outputs. So go figure. Doubt that drifts.Who drew these diagrams and parts lists?The board layout shows U203 not as an IC (they have notches on them indicating Pin1 end) but as a connector, and all other connectors are drawn accordingly. I don't have access to the unit right now to confirm visually. I also did not search any drawings for the IC version of U203 if there is one.I don't think the exact frequency of the oscillator has any effect on DC offsets at all. Just my opinion...

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: August 04, 2022, 03:48:53 pm
content: Apparently SRS decided it was not redundant to use the same designation for parts if it was on another board...U203 is on the lower board.

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: August 04, 2022, 04:04:45 pm
content: U203 is the ovenized Osc option connector... on the TOP PCBA. You can see Shahriar disconnecting it at9min 12 seconds here...

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: August 04, 2022, 06:32:32 pm
content: Helps to save some time using PDF Page# when troubleshooting using the Elektrotanya manual which contains these drawings...PDF Page Desc. Sheet140 Upper PCBA Layout DWG n/a141 Lower PCBA Layout DWG n/aSCHEMATICS:BOTTOM PCBA:142 PWR Supp, Fan & Reset SHT1143 MicroProc Sys SHT2144 Display, Lamps, KYBD SHT3145 Ribbon Cable, Trig, & Sync Sel SHT4146 GPIB & RS232 SHT5147 OUTPUT AMP SHT6148 OUTPUT ATTN SHT7TOP PCBA:149 Ribbon, A/Ds & D/As SHT8150 Clocks & Ref PLLs SHT9151 Phase Accumulator & Waveform RAM SHT10152 DACs for Amplitude & Sweeps SHT11153 Waveform DAC SHT12154 Filters & Doubler SHT13155 Sync & Gain Adj. SHT14Front Panel PCBA:156 Front Panel Disp/KYBD SHT15157 Front Panel Segments SHT16

author: bostonman
author_rank: Super Contributor
timestamp: August 05, 2022, 10:55:26 pm
content: I'll look. I didn't get a follow up notification for some reason, so I didn't see your recent postings.Did you already post this, do you know there are two U111 ICs?I'm growing frustrated chasing reference designators. By the time I find what I'm looking for it's either a duplicate number and/or I've forgotten what I'm trying to measure.I checked the crystal on the top board (I don't have access to the schematics at the moment) on a frequency counter and that circuit seems solid.Since chasing these components is making things difficult, maybe cross referencing our measurements will improve efficiency. I was thinking, maybe a reference voltage has become noisy causing a DAC or ADC to have noise on it.Page 1 has most of the reference voltages from what I can tell. This issue has to be very sensitive since adding a logic analyzer caused the same error on the good unit. I'm still thinking a LSB issue which a noisy voltage would cause.

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: August 08, 2022, 03:09:45 pm
content: More than a few topics here.addressing them in order..."I'll look. I didn't get a follow up notification for some reason, so I didn't see your recent postings."Unsure what is being refernced here."do you know there are two U111 ICs?"as mentioned earlier... SRS has made it clear...they reserve the right to duplicate any reference number as long as it is on a different PCBA!!!"I checked the crystal on the top board (I don't have access to the schematics at the moment) on a frequency counter and that circuit seems solid."It is actually wildly variable though, unless your ambient room temp is held constant, which is why they offered the OVEN option, and an external sync 10MHz input available for even greater stability."I was thinking, maybe a reference voltage has become noisy causing a DAC or ADC to have noise on it."The only real reference voltage (5v ref) is created at the AD586 5 volt Reference IC, and that is for theDACs. AD Spec is: OUTPUT NOISE 0.1 Hz to 10 Hz 4 μV p-p. So you could look at that easy enough."Page 1 has most of the reference voltages from what I can tell."As above... there is ONE 5 Volt reference voltage, the AD586, but it is on page 142 of the PDF, which is SHEET 1.Page 1 would be the cover page.All the other voltages are from regulator circuits, and Vreg IC's.

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: August 08, 2022, 03:59:10 pm
content: Sorry, there is also on PDF page 153 (sheet 12) the -1V Ref U501 LM337L for the Waveform DAC U500.

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: August 08, 2022, 04:33:20 pm
content: Another thing to add to the list of annoying things in the "Manual"...The description of getting the unit into CAL mode, or CAL mode "off" is pretty straightforward.However, when they state that the values can be entered either way by using the MODIFY keys (UP/DOWN) or the Keyboard numbers directly is not telling the entire story. Only when the CAL VALUE is flashing will it accept a real change, and when using the Keyboard numbers directl you MUST hit one of the VALUE keys to get the flashing CAL VALUE. Hit DEG MHZ KHZ or HZ, otherwise it does not take your entered value. They also go on and on in several places about STORING the values into RAM... as if you need to do something special to get them stored. Nope, just switch off the #2 switch on sw300. too hard to tell you that. Assumption?

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: August 10, 2022, 03:04:27 pm
content: Shahriar uses his nice Oven based option timebase DS345 in his latest video of the SRS SR830 Lock-in Amplifier. Quite an interesting video.

author: bostonman
author_rank: Super Contributor
timestamp: September 25, 2022, 02:26:09 pm
content: Have you got anywhere with your unit?Due to many other ongoing projects, I was forced to screw it together and stick it on my shelf.Something odd that I noticed: the PCB has a rubber foot, I think it's there to prevent the PCB from touching the metal case when it's swung open. For whatever reason, the thing began going from rubber to a thick liquid state. At first I thought it was touching a lamp I had near it (and maybe it did), but it never seemed to re-harden. Each time I tough it, I'd have black tar residue on my finger.Before screwing the cover on, I removed it and applied some electrical caulking in place of the rubber foot. To make sure I didn't forget to connect anything, I powered the unit (with the caulking still wet) and the screen displayed a different error.I'm wondering if maybe some impedance issue is causing these units to fail. Maybe it's coincidence, but seems odd I've got the same error during many times I've powered the unit, and suddenly get a different error when I put caulking on the board.In any case, it's on my shelf still in a broken state in hopes someday I return to working on it, or find a solution online.

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: September 26, 2022, 03:11:52 pm
content: Sadly, I was burning it in, and all seemed stable for a few weeks, then suddenly offset drift began again at output of u600 LT1008. So still trying to know why it happens.One thing that does happen on early s/n units... the 60 pin connector comes loose, and you lose display LEDs... front panel goes completely dark. Happens from repeatedly opening and closing the top board.On later s/n units they put silicone on the top board connector, and the bottom board connector as well.Interesting about the melting foot. I would also check the 60 pin connectors.

author: bostonman
author_rank: Super Contributor
timestamp: September 27, 2022, 02:24:04 am
content: I've removed that connector and cleaned the pins with cleaner, however, I've also experienced a screen display loss when I've forgotten to connect it.Between connecting a logic analyzer previously to an IC chip and the wet caulking causing different errors, I wonder if an ECO exists at the SRS due to an improperly sized trace on the PCB. Or maybe a small capacitor that has gone out of spec causing an issue with the feedback circuit (which would be similar to an impedance mismatch with an etch).Just seems odd I got a different error just by connecting a logic analyzer to an IC (I forget which one, but it's listed in a previous post) and a different error with wet caulking.

author: bostonman
author_rank: Super Contributor
timestamp: January 23, 2023, 12:34:14 am
content: I haven't seen any updates and wondering if you've got anywhere with this issue.

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: January 30, 2023, 06:43:43 pm
content: I just now noticed your post.I have taken a break from it, but yesterday I returned to it.I am now concentrating once again on my original assumption the problem is in the output amp.I found several open transistors, including the finals. I replaced them. I found more, and am taking another break from it. The lower board is not anywhere near as easy to work on as the top board. I will be back at it again. I am determined to not let this unit win the fight.

author: bostonman
author_rank: Super Contributor
timestamp: January 31, 2023, 01:47:17 am
content: You found several open transistors?I'm assuming you mean a bunch were bad, however, this indicates the problem isn't with one or two components, but an entire group, correct?

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: February 03, 2023, 04:50:32 pm
content: Yes... mostly on the Positive Half of the diff amp ckt. NPNs, and the Finals of both halves of the single ended output. There may be more. best to find them all before powering up again.Lots of work ahead. Might be a good idea to power from external +/- 15V supply measuring current.

author: bostonman
author_rank: Super Contributor
timestamp: February 03, 2023, 05:38:37 pm
content: This is somewhat upsetting news. I didn’t realize several bad transistors were part of this failure. I thought it would be a single component.

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: February 06, 2023, 05:33:07 pm
content: There could be considerable collateral damage in this ckt. as I mentioned, working on the bottom board is difficult. Getting close enough to it wearing magnification to see what you are doing is tough. Especially when almost half blind. Hopefully this round will have a better outcome using current limited, and display indicated, external supply for power.

author: bostonman
author_rank: Super Contributor
timestamp: February 07, 2023, 06:14:03 pm
content: Due to the recent pieces of information regarding potential collateral damage and the amount of damaged transistors, maybe it's not worth the time to repair?Are the bad transistors an indication someone plugged something into the output connector that shouldn't have been and blew up the whole input section?

author: bostonman
author_rank: Super Contributor
timestamp: June 21, 2023, 02:28:28 am
content: Did you ever get anywhere with this or give up?