Author Topic: Repair : 94' Keithley 2002 8.5-digit DMM , good ol' cap leaks destuction derby..  (Read 14444 times)

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Offline TiN

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Some of 8.5d-nuts might notice this poor 2002 gone recently on ebay.. And wonder no more, which pesky Keithley-maniac got it..

Just got back home after trip, could not resist to take a sneak peak inside, to get idea what's we dealing with.

Appetizer photos for starters...



Hood removed..



Firmware is A05, unit already equipped with MEM2 DS1248Y option (very old NVRAM chip though, likely dead/near death).



A/D board 2002-162 Revision B, very same as my newer 2007-year Model 2002. :



LTZ1000A reference circuitry, DCV/Ohm blocks with VPG foil resistors, pair of LTC1043-based reference converters... All looks good in this area. Date codes on chips are 1994, so this meter is 22-year old.



What this means? It means capacitor disasters! This is reason of why unit get destroyed and require bit of advanced repair now...



1000uF 50V cap at earth-references circuitry leaked it's nasty electrolyte on PCB, corroding PCB tracks, components pins and causing short. Stuff die and blows up as a result.



More crispy tasty photos:




So if you still have some instruments more than 10 years old and did not replace all electrolytic capacitors, close this thread and do it NOW. :)

To be continued...

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Offline ManateeMafia

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Do the transformer windings still measure ok? It looks like it cooked in its own juices for a while before someone noticed the smell of burning pcb.
 

Offline TiN

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Yes, xfrmr is OK. Resistance measurement fine and it's working ok in one of 2001's.
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Online TheSteve

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Wow, this one should be quite the challenge - those are some seriously hungry capacitors, they want to eat everything.
VE7FM
 

Offline quarks

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Looking forward to follow another excellent thread from you.
Thanks for sharing and good luck
 

Offline ketil b

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Hi

So the pic of the bottom of the power supply looks familiar. I go a 2001 just before the new year that wood not power up, turns out that the big mosfet and power resistor on the primary side of the power supply had both failed open, one of the symptoms of this was R102 and R103 where being cooked, almost got throw the pcb before I caught it.

thanks

ketil
 

Offline TiN

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One of my 2001's had exactly same issue before, and working well repaired, so that was one of reasons why I hit bid button on this 2002. Second reason was due to my wish of making complete schematics of 2002 as well, not only 2001, and I did not want to risk my first 2002.
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Offline TiN

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Day 1 - cleaning analog board, check digital & FP

Repair will start from removing all affected by electrolyte gunk parts and cleaning PCB till it's shiny.



No visible damages on secondary analog power, which is good news, making high chances that all analog circuits is still nice and working.



Methodology is simple. Desolder EVERYTHING in all areas where electrolyte was spread. Jelly-bean parts replace with brand new components without any testing, expensive/custom parts to be cleaned and washed in IPA, checked and then soldered back. I'll make a list of everything need replacement and place order on Digikey next days.

Now, test digital board and FP, using recently bought Keithley 2304A PSU to provide +6.3V at U629 LDO input.



Good news, digital board works fine, VFD is OK too.



It's bit aged on edge segments, but overall pretty good shape for 22-year old unit. I'll use it as is. Overall current consumption of digital+FP boards = ~0.66A.

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Offline krivx

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You have some very nice images of that 2-sided power board, probably good enough to make some reverse-engineered gerbers to provide cheap replacement boards. Have you seen this thread? https://www.eevblog.com/forum/eda/image-to-gerber-converter/
 

Offline TiN

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I'm not really seeing how that can help in this particular case :) Nice idea though.
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Offline krivx

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No, I guess it's not needed in this case. It just seems likely that might end up a few more of these units at some point  ;D
 

Offline TiN

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Ordered parts from DK.

Started assembly of what I already have.



Mains area cleaned and ready for repairs...

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Offline TiN

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Someone forgot this poor DMM? That ain't me.

Yesterday night I replaced all components in earth-referenced area before the transformer, as well as 2xDG444,DG408 (interesting to note, 2002 using different switches there, instead of DG211 on K2001, shooting for lower leakage?), 1xAD711, 1xLM311, pair of 4094 SRs, 79L05 etc.

Also enforced few vias by putting small copper strand thru them and soldering both sides, as well as few traces were repaired as they were eaten away. One of pads of bridge rectifier was loose, so I had to jump wire it on bottom side. Blown resistors were fixed on same location above hi-temp mylar using piece of copper plate.



PCB was delaminated in few areas, but nothing we can do about that. Should be still fine, as these areas are not high importance of analog path.

End result look like this:



Power switch, Q101 transistor, 2 and 5 pin jacks, fuse holder, LM317T were checked, thoroughly cleaned and reused. It ain't looking pretty, but should do the job well.

Bottom side:



Every single resistor and cap were replaced here, some parts taken from my donor 2001, most of parts brand new from DigiKey.

And, first power on, smoke test passed, no surprises. Moment of truth, self-diagnostics test..



Yay, this fella want to play! I ran it 10 times in a row, all tests pass flying colors.

Hooked it up in parallel with 3458A, which is now calibrated to measured LTZ1000A module (live log data), it read 10ppm high. Not bad, considering last calibration in 2009 and repairs :)

So the outcome of this project was just like I expected and hoped for, just fix of electrolyte mess, replace gunked parts and all is back again.  :-DMM
Seems it's time to sell few 2001's..
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Offline ManateeMafia

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 :-+ Another Keithley returned to service.

Interesting fix with the burnt area. Will have to remember that.
 

Offline TiN

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Interesting fix with the burnt area. Will have to remember that.

Professional way of doing that would be milling/cutting complete burnt area, putting FR4 patch inside and fixing it with board epoxy. Then jump-wiring missing/broken connections with proper wire around. Carbonized FR4 is very leaky/partially conductive, so you don't want any signals running over it.

I think we will be back to proper way of doing it, on some 3458A board which you may know of. Time, time...  :phew:
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Offline ManateeMafia

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I thought something like this anchored to the pcb with epoxy ...

http://www.robotshop.com/en/prototyping-board-sop8-dip8.html?gclid=CNGruPOc08sCFUc2gQodnhMJ7g

Couple bits of wire through the pcb on each side and you are back in business.
 

Offline doktor pyta

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In my K2001 I used plastic spacer to lower heat transfer from the hot PCB to the body of the capacitor.
I may find the TME part number if someone is interested.

Offline NANDBlog

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Very nice fix so far.
But if corrosion started on a trace, it will slowly eat the trace the entire length. Would not it be better if you would cut the traces somewhere and completely remove them?
 

Offline TiN

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All open traces were cleaned to shining copper and I had tinned them with solder. There was a lot of cleaning with IPA many times as well, to ensure all electrolyte is removed.
I'll let you know if that's not good enough in 2026 of before that if meter fails earlier :)

doktor pyta

Neat tweak, but I'm afraid it would not help much, as case is closed and there is nowhere for heat to escape. So with spacer or without it will all be cooking there.
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Offline doktor pyta

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Tin
1. For sure this changes the ratio of radiated heat to conducted heat. I haven't made the measurements so I cannot give You the numbers.
2. In case of the leak the spacer should slow down the PCB destruction process (+ I hope that the leak could be easier seen on the surface of the white spacer).

All in all we will see in few years how much this helps.
« Last Edit: March 22, 2016, 01:18:53 pm by doktor pyta »
 

Offline NANDBlog

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All open traces were cleaned to shining copper and I had tinned them with solder. There was a lot of cleaning with IPA many times as well, to ensure all electrolyte is removed.
I'll let you know if that's not good enough in 2026 of before that if meter fails earlier :)

doktor pyta

Neat tweak, but I'm afraid it would not help much, as case is closed and there is nowhere for heat to escape. So with spacer or without it will all be cooking there.
Yes, I'll make sure to check back in ten years whether or not it is working. Although probably in ten years we will not be using FR4 anymore, but the information is still going to be useful for repairs.
 

Offline TiN

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I'd expect FR4 would still be around just as we have it still. And overall concept (remove damaged parts, put good ones back in, mate the connections) is to remain valid more decades from then. You and me will have a gray beard by then, so bigger question remain would we care about this meter then :).
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Online TheSteve

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Nicely done, seemed just a little too easy!
VE7FM
 

Offline Le_Bassiste

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seemingly not entirely on topic, but still...
there are a lot of tear down pictures of KEI2002 and KEI2001 out there, but only a very few give a clear view on the top black plastic shroud that covers most of the analog circuitry. what i've noticed so far:
the shrouds for KEI2002 and KEI2001 are different:
KEI2001 shroud doesn't have any air vents at its circumference, thus protecting the analog circuitry from any "busy" air.
KEI2002 shroud has a vent at the fan-side and an exhaust vent at the opposite side, somewhere in the area of connector P1027. also there is a transparent air duct installed over the fan.

and here is my question: what is the correct placement of the transparent air duct in a KEI2002?
is it like this, allowing for some airflow onto the mains controller V105?
https://xdevs.com/doc/Keithley/2002/photo/Chuck/img_0113_fan%20baffle%20detail.jpg

or is it like this, where the entire airflow is directed into the shroud?







 
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Offline TiN

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On my 2007 year unit - yes, it's like on your photo, all air goes into the shroud (which is confusing to me, to say at least).
On older unit shown here in thread - shroud is 100% same as Model 2001, without any vents or openings.
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