Author Topic: Standford Research DS345 Error  (Read 10142 times)

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Offline bostonmanTopic starter

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Re: Standford Research DS345 Error
« Reply #50 on: July 28, 2022, 02:39:53 am »
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.

Quote
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.

This 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.
 

Offline SoundTech-LG

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Re: Standford Research DS345 Error
« Reply #51 on: July 28, 2022, 02:53:37 am »
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.
 

Offline bostonmanTopic starter

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Re: Standford Research DS345 Error
« Reply #52 on: July 28, 2022, 03:01:35 am »
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.
 

Offline SoundTech-LG

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Re: Standford Research DS345 Error
« Reply #53 on: July 28, 2022, 03:22:33 am »
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???
 

Offline SoundTech-LG

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Re: Standford Research DS345 Error
« Reply #54 on: July 28, 2022, 03:34:05 am »
Sorry meant U600 in the Output amp section. Not the other one that's another AD834 Doubler.  :scared:
 

Offline bostonmanTopic starter

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Re: Standford Research DS345 Error
« Reply #55 on: July 29, 2022, 02:13:36 pm »
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.
 

Offline bostonmanTopic starter

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Re: Standford Research DS345 Error
« Reply #56 on: July 31, 2022, 12:53:53 am »
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.
 

Offline bostonmanTopic starter

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Re: Standford Research DS345 Error
« Reply #57 on: August 01, 2022, 01:16:45 am »
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
 

Offline SoundTech-LG

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Re: Standford Research DS345 Error
« Reply #58 on: August 01, 2022, 04:36:39 pm »
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?
 

Offline SoundTech-LG

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Re: Standford Research DS345 Error
« Reply #59 on: August 02, 2022, 12:29:50 am »
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
 

Offline bostonmanTopic starter

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Re: Standford Research DS345 Error
« Reply #60 on: August 03, 2022, 06:16:14 pm »
Quote
Are you able to actually enter user offset voltages using the keypads, or no? Any changes seen at U600 if you do so?

Sorry 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.

 

Offline bostonmanTopic starter

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Re: Standford Research DS345 Error
« Reply #61 on: August 04, 2022, 02:28:55 am »
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.

 

Offline SoundTech-LG

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Re: Standford Research DS345 Error
« Reply #62 on: August 04, 2022, 03:33:59 pm »
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?  :palm: 
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...
 

Offline SoundTech-LG

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Re: Standford Research DS345 Error
« Reply #63 on: August 04, 2022, 03:48:53 pm »
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.
 

Offline SoundTech-LG

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Re: Standford Research DS345 Error
« Reply #64 on: August 04, 2022, 04:04:45 pm »
U203 is the ovenized Osc option connector...  on the TOP PCBA. You can see Shahriar disconnecting it at
9min 12 seconds here... 

 

Offline SoundTech-LG

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Re: Standford Research DS345 Error
« Reply #65 on: August 04, 2022, 06:32:32 pm »
Helps to save some time using PDF Page# when troubleshooting using the Elektrotanya manual which contains these drawings...



PDF Page      Desc.                                                                      Sheet

140                Upper PCBA Layout DWG                                     n/a
141        Lower PCBA Layout DWG                                      n/a

SCHEMATICS:

BOTTOM PCBA:
142                PWR Supp, Fan & Reset         SHT1
143                 MicroProc Sys            SHT2
144                Display, Lamps, KYBD         SHT3
145         Ribbon Cable, Trig, & Sync Sel      SHT4
146         GPIB & RS232            SHT5
147                 OUTPUT AMP            SHT6
148         OUTPUT ATTN            SHT7

TOP PCBA:
149                 Ribbon, A/Ds & D/As         SHT8
150         Clocks & Ref PLLs         SHT9
151         Phase Accumulator & Waveform RAM   SHT10
152         DACs for Amplitude & Sweeps      SHT11
153         Waveform DAC                                                       SHT12
154                 Filters & Doubler         SHT13
155         Sync & Gain Adj.            SHT14

Front Panel PCBA:

156         Front Panel Disp/KYBD         SHT15
157                 Front Panel Segments                                           SHT16            
« Last Edit: August 04, 2022, 06:42:10 pm by SoundTech-LG »
 

Offline bostonmanTopic starter

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Re: Standford Research DS345 Error
« Reply #66 on: August 05, 2022, 10:55:26 pm »
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.

 

Offline SoundTech-LG

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Re: Standford Research DS345 Error
« Reply #67 on: August 08, 2022, 03:09:45 pm »
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 the
DACs. 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.


 

Offline SoundTech-LG

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Re: Standford Research DS345 Error
« Reply #68 on: August 08, 2022, 03:59:10 pm »
Sorry, there is also on PDF page 153 (sheet 12) the -1V Ref U501 LM337L for the Waveform DAC U500.
 

Offline SoundTech-LG

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Re: Standford Research DS345 Error
« Reply #69 on: August 08, 2022, 04:33:20 pm »
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?
 

Offline SoundTech-LG

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Re: Standford Research DS345 Error
« Reply #70 on: August 10, 2022, 03:04:27 pm »
Shahriar uses his nice Oven based option timebase DS345 in his latest video of the SRS SR830 Lock-in Amplifier. Quite an interesting video.



 

Offline bostonmanTopic starter

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Re: Standford Research DS345 Error
« Reply #71 on: September 25, 2022, 02:26:09 pm »
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.
 

Offline SoundTech-LG

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Re: Standford Research DS345 Error
« Reply #72 on: September 26, 2022, 03:11:52 pm »
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.
 

Offline bostonmanTopic starter

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Re: Standford Research DS345 Error
« Reply #73 on: September 27, 2022, 02:24:04 am »
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.
 

Offline bostonmanTopic starter

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Re: Standford Research DS345 Error
« Reply #74 on: January 23, 2023, 12:34:14 am »
I haven't seen any updates and wondering if you've got anywhere with this issue.
 


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