Keithley 2002 repair help

[nikonoid]

Hello guys,

I am new to this forum. I had been reading for a while, but this is my first post.

I have a Keithley 2002 that I am trying to repair. It is quite old, chips are from 1998 the serial starts with 072XXXX. The board looks clean and capacitors seem to be in a fine shape.

The major issue with the unit was the Front/Back switch. For now I hardwired the switch and was able to get the unit to pass self test. Can someone please recommend a source for replacement switch. I believe it is SW-468, but I cannot find a source for it. Would there be any special considerations for replacing it?

Also the unit came to me without a fan. I am not sure what to make of it. It had the opening in the black protective cover and plastic air guide, like in the newer 2007 unit TiN has. For now without a fan I am limiting the use of meter to 10 minutes at a time.  Can someone recommend a replacement fan and what sort of connector I would need to get to install it?

Thank you very much. If I can somehow contribute to the forum, please let me know.

[TheSteve]

Welcome to the forum! The 2002 is a great machine - certainly worth the effort to get it operating 100% again. I think your first call should be to Tektronix/Keithley and ask to speak to the parts department. You should be able to purchase the parts you need direct from the source.

[TiN]

Welcome to forums. K2002 is my second favourite meter  .

Ask Keithley/Tektronix, they might sell you switch for replacement. It's not too expensive considering the cost of the meter.
You can see my articles about 2001/2002 (here and here and here) but from my memory fan is 40x40mm 12V 0.1A. For my meters I've used this one from Digikey. Bit more powerful, as I tend to run meters in warmer ambient.

Also replace all electrolytics on both boards, even if they look good! They are badly thermally stressed in 2001/2002, so don't play gamble here.

If you can take photos of your unit, would be nice to have. What is your firmware version? Would be good to add into collection if it's not the one we already have.

[nikonoid]

Glad to be here.

Thank you for suggestion to call Keithley for spare parts, I did not even think about this option.
The switch was surprisingly less than I expected - $12 and fan surprisingly more - $47. Now I have to wait for both to arrive.

As firmware is concerned, on start is says "Rev. A06   A02 IEEE Adr. = 16". Not quite sure what A02 is referring too.

I will take photos and post in few days. Is it OK to post full resolution photos?

For electrolytics could it be sufficient to test them with LCR miter before replacement? My soldering skills are a bit less than expect, so I would not want to risk replacing something that is not necessary.

I am still going through complete checkout of the meter and just found that resistance reads wrong, but only on a single range (2MOhm) and only in 4 wire mode. Other ranges work fine and in 2 wire mode all ranges read fine. Any suggestions for what to look for? Can I re calibrate this single range?

Thanks.

[TiN]

Go for full resolution. Forum have limitation, so you can upload to my ftp (how-to link in my messages footer), I'll add them nicely to forum for you.
Always a pleasure to see one more 2002 saved from dumpster diving.

Just replace the caps, don't waste time with checking them. If you excercise bit of care, replacement will be just fine. Avoid touching board surface/components with fingers though, handle it by edges only to avoid leakage contamination.

Calibration is bit complex on 2002, so I'd wait till you get switch replacement to see if issue stays. Could be leakage in switch causing problem.

[Samogon]

Replacing caps is mandatory!
And if you hesitate to re solder caps how you are going to replace switch which is much harder to do and requires skills?
I can suggest my help replacing caps and switch, i have proper tools for it (your shipment and components). I have two 2001 on my queue for caps replacement.
K2002 is not device to gain soldering skills. I would start with something less gentle and expensive.

Dont want to be harsh. But i can suggest to buy desoldering gun for it
like https://www.amazon.com/Desoldering-Station-Digital-Temperature-Controlled/dp/B00KQ6PR6K/ref=sr_1_8?ie=UTF8&qid=1494359041&sr=8-8&keywords=desoldering+gun
or more advanced but more expensive
https://www.amazon.com/Hakko-FR300-05-P-Desoldering-Tool/dp/B00KWM69C4/ref=sr_1_4?ie=UTF8&qid=1494359041&sr=8-4&keywords=desoldering+gun
I personally use
https://www.amazon.com/gp/product/B00NS49ZB0/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
but it requires compressor to work. so whole set is bit expansive, but i like it.

[nikonoid]

Thank you, Samogon.

This is a very kind offer and I do appreciate it very much.

I am not a complete novice and have done a fair share of removing large connectors. However I do not solder on a regular basis and I never worked on the instrument this sensitive before, so I may need some guidance.   

I do have a vacuum desoldering station (very old PACE Micro that I bought used and fixed). I am planning to modify one of the tips to work with slightly bigger 40 mills legs on the switch. I also have an ESD mat to work on.

The questions that I would have are:
1) Should I wear gloves? What kind (rubber/cloth)?
2) Is using regular 60/40 solder with flux core good enough, or do I need some kind of low thermal solder for the switch?
3) Is alcohol (or samogon  ) sufficient for cleaning after soldering
4) Are there any special tricks or tips for removing Analog and Digital boards from the case?
5) Should I replace capacitors that are far away from the transformer and voltage regulators?
6) In some videos, including TiN's video of K2002 repairs, I saw new solder being added to the joint before desoldering it. Why is that?

Thanks in advance for answers.

In case someone would find this useful here is a list of every electrolytic capacitor in K2002 with their DigiKey part numbers. They all are Nichicon beside 15000uf that is Illinois Capacitor (Nichicon was not in stock anywhere). Most original capacitors are VX(M) series and these are these UVX series. I am hoping these are essentially the same.
 

Code: [Select]

Index QT Part Number Description                 Cust        Stock Backorder Unit Price USD Ext USD
1 1 UVZ1H102MHD CAP ALUM 1000UF 20% 50V RADIAL C104      1 0 0.94 0.94
2 2 493-1323-ND CAP ALUM 2200UF 20% 35V RADIAL C112,C113 2 0 1.31 2.62
3 1 493-1288-ND CAP ALUM 2200UF 20% 16V RADIAL C114      1 0 0.72 0.72
4 2 493-1358-ND CAP ALUM 470UF 20% 63V RADIAL C116,C117 2 0 0.76 1.52
5 2 493-1322-ND CAP ALUM 1000UF 20% 35V RADIAL C118,C119 2 0 0.7 1.4
6 1 493-1266-ND CAP ALUM 100UF 20% 10V RADIAL C206      1 0 0.28 0.28
7 3 493-15350-ND CAP ALUM 22UF 10% 16V RADIAL C247,C250,C253 3 0 0.38 1.14
8 1 1572-1350-ND CAP ALUM 15000UF 20% 16V AXIAL C611      1 0 5.15 5.15
9 3 493-1287-ND CAP ALUM 1000UF 20% 16V RADIAL C624,C630,C633 3 0 0.52 1.56
10 1 493-14496-ND CAP ALUM 47UF 10% 35V RADIAL C625      1 0 0.45 0.45
11 1 493-1369-ND CAP ALUM 2.2UF 20% 100V RADIAL C912      1 0 0.28 0.28



 

[Samogon]

He he i glad you have got my nickname properly

1 nitrile gloves probably will work keeping body oils off board.
2 60/40 is pretty much standard i use 70/30.
3 i use isopropyl 99% it is much better than 70% (samogon usually 70% but it has surrogates in it and cant be used to clen pcb)
4 most of the removal procedures are stright forward, but take extreme care removing input ferrite filters their plasric eclosures can be easily broken so disconnect cables from input connectors first then gently lift them from the grooves. Also desolder front white wire from analog board.
5 all capacitors have to be replaced, i had error 102.1 and thought it is eeprom, but it was small 47uf cap
6 adding solder really helps to break oxidized surface and adds thermal mass to the tip application point.

Hope it helps

[nikonoid]

Thanks a lot. This will be very useful when parts arrive.

Today I checked date codes on capacitors and they are all originals from 97 and 98. So I will be changing all of them.

[nikonoid]

While I am waiting for parts here are some images.

Digital side:


Appears to be revision 06K:



Firmware was possibly upgraded to A06 by Keithley. See the glue residue from previous sticker. The transformer looks very cruddy.







Analog side. See the plastic air guide, like in the later TiN's unit. The hole in the black shield was cut too.



Revision E of the analog board:


Capacitors to be replaced and again very questionably looking transformer. Should I bee worried?



ADC Board:


Precision resistor networks:



These regulators get really how and their heat sinks look a bit rusty. Is that normal?



More to follow after I receive parts and attempt to fix it.

TiN: Thank you or hosting photos.

[Samogon]

Tranformer is ok. They all look like this, melted, but it is not.
Accorfing to photos, you got nice unit. No acid damage.

[nikonoid]

Thank you for reassurance on the transformer, Samogon.

Today I took the analog board out. It took quite a bit of effort. I think the manual is somewhat incorrect. They are recommending desoldering the white wire when disconnecting the rest of input connectors. In practice it seemed that the best course of action is disconnect the rest of front and back inputs, keep the white wire attached until the Analog Board is out of the case. Only then you have direct access to the back side of the board and can easily desolder it.

The good news is the the faulty inputs switch is off. Once I customized the vacuum suction tip to have wider opening: 0.052", removing the switch was a breeze.

Will be changing capacitors in few days.

Meanwhile I have another question, the board I have seem to have a bit of dust on it, mostly by the fan (including spots under the shield).
Should I blow this dust away? Is there a preferred method?

Manual suggests compressed nitrogen, but I do not have it. Would air from a compressor suffice or should I use IPA instead? Thank you very much.

[macboy]

Meanwhile I have another question, the board I have seem to have a bit of dust on it, mostly by the fan (including spots under the shield).
Should I blow this dust away? Is there a preferred method?

Manual suggests compressed nitrogen, but I do not have it. Would air from a compressor suffice or should I use IPA instead? Thank you very much.

Don't use air from a compressor unless you have very good filtration. By that I mean 0.02 micron or better coalescing filter to remove oils in addition to particulates. Otherwise you will contaminate the board with compressor oils. You should be able to get ultra low residue canned duster from you usual electronic supply shops. Don't use the normal consumer grade stuff, in most countries it has a bitterant that will leave residue everywhere.

[nikonoid]

Thanks for the suggestion. Would "MG Chemicals Super Duster 134" or "MG Chemicals Super Duster 152" be a good enough for the task?

[macboy]

Thanks for the suggestion. Would "MG Chemicals Super Duster 134" or "MG Chemicals Super Duster 152" be a good enough for the task?

Either looks fine, both are "pure" (single ingredient) and residue free. The 134 is non-flammable and approved for use on energized circuits. The 152 is flammable under some conditions, but I think it is less expensive as well. Use with good ventilation.

[nikonoid]

Just ordered one. Thank you.

Changing the front/back switch was a breeze. I am surprised that changing capacitors is more difficult than I expected. Holes in the board are very very tight, so vacuum desoldering iron does not help much.  I have to move each leg a little bit at a time. Any additional tips there?

[Le_Bassiste]

well... not directly related to desoldering the caps, but to general handling of the p.c.b.
i'd suggest that you do not try to clean the entire pcb by any means, in order to absolutely avoid any contamination. just clean the areas that you have been working on, and you should be fine. this is IIRC also stated somewhere in the repair manual.
a pcb being contaminated by residues of foreign matter (that is otherwise just sitting on the components, not doing any harm at all) dissolved by cleaning agents, and then evenly distributed across the whole board will probably send your fine meter to the point of write-off.
of course, ymmv, and i'm being probably a tad too paranoid about this. it's just that my kitchen-sink equipment would simply wreak havoc on the pcb if i would try to do this, even with gallons of cleanest IPA, N2 and whatnot at my hand...
so, the way i tackled that on my 2002 was just to get out a pair of nitriles, stop breathing, remove all caps, clean the areas with KONTAKT LR and cotton swabs, mount the new caps, then again clean the areas and close the box, and breathe.

[nikonoid]

I am almost done recapping. Digital and analog boards are done. More high res photos and more questions to follow soon.

Meanwhile I am facing a new dilemma now. According to manual display board contains one electrolytic capacitor: 2.2uf 100v. However when I opened that board I saw the his:


I have never seen electrolytic like that. Should I replace it? What do I replace it with? I could not find the same Philips available for sale.

Thanks in advance.


Sent from my iPhone using Tapatalk

[coromonadalix]

they are series 139  Aluminium electrolytic capacitors  long life  models, i would substitue only with an original part ...  your dallas DS1243 "black chip" 64K NV SRAM with Phantom Clock is dated form year 96, if its not dead  change it.

WARNING :  i dont know if it retain any calibrations, i dont think so

[nikonoid]

Thank you, coromonadalix,

This 2.2mf 100v capacitor is a hard to find item: discontinued and non stocked.
I managed to locate and purchase 25 pieces, but I only need one.

If anyone here is recapping their Keithley and need one, send me a message and I will hook you up.

[Samogon]

You went too far with recaping

[Smith]

The new units have the same cap, but manufactured by BC. I replaced the cap on mine after replacing the VFD. It went bad within 8 hours and overloaded the 60v of the VFD. I placed the old Philips cap of the old VFD on the new VFD, and it's still working fine.

[nikonoid]

Smith, thanks for the photo. This is right on. And here is my display board:


As soon as I opened it, I could see signs of extreme overheating. See by the contact switches. The board became more transparent and showed rainbow colored fringe, sort of like you get with a drop of gasoline in the water. The damage almost looked worse on the switch side than on component side. The heat pattern seemed to be centered at Q901 component. It is near capacitor, but not directly next to it. The transformer also looked burned. That said when I powered the meter up, the display worked without any problems. Please let me know what you think.





Here is the rubber keyboard. I cleaned it and switch contacts with IPA. The discoloration on rubber looks strange:


When I removed analog board and lower shield, I also discovered another spot that looked like overheating. It is right at the spot where lower shield has a heat transfer sponge. It is in the lower right corner of the photo below and also magnified in the photo after, where I was able to photograph rainbow discoloration on the board.



What could it be? Should I be concerned?

Here is a quick grab of the back of a digital board and also the ESD safe sponges I used with IPA for cleaning:



And finally the badge of honor 




Please let me know if you have any ideas about two overheated spots (display and analog boards). Thank you.

[Le_Bassiste]

yes, these pesky VFD transformers are real cookers! don't know how to handle that, though.
as for the discoloration of the area under the heat sponge, that is not caused by overheating. it is caused by the sponge itself, sweating out some of the silicone over the years. if you look closely, you will find traces of that on top of the pcb as well, where it crept through the vias. the extra conformal coating on the pcb in the area, where the sponge sits, was discussed before:
https://www.eevblog.com/forum/repair/repair-94'-keithley-2002-8-5-digit-dmm-good-ol'-cap-leaks-destuction-derby/msg1016968/#msg1016968
i _assume_, that the seemingly useless and contradicting application of the coating over guard traces was intended to protect that area against moisture getting trapped underneath.
so, i would go with TiN's notion here: leave as is.

edit: see also:
https://www.eevblog.com/forum/repair/repair-94'-keithley-2002-8-5-digit-dmm-good-ol'-cap-leaks-destuction-derby/msg1017683/#msg1017683

[Le_Bassiste]

hmm, after another look at your photos, i now see that it is not the transformer that caused the brown spot on the pcb,    it's one of the two push-pull transistors on the primary side.
given the age of the instrument and the fact that the supply of the display is still giving the right voltages for filament and anode, you probably shouldn't be too worried about it.
the only thing that you could do is to exchange the transistors with some better ones. don't know from top of my head whether these are BJTs or MOSFETs, have a look at the KEI2001 schematics (VFD supply should be same as in KEI2002, but is located on digital board) on TiN's site to find out.