Restoration glory of Keithley 2001 DMM

[michaeliv]

The manual with part numbers is here ...
https://xdevs.com/doc/Keithley/2001/2001-902-01.pdf

The transformer part number in the manual matches what is printed on the side (TR-280). I have had a few issues tracking down new part numbers with Tektronix as some have changed. For example a letter (A,B,C,etc.) has been added to the part.
The manual also lists test voltages. I don't think any real t/s procedure has been written. The current method of repair is to remove all the electrolytic caps around the supplies and inspect for leakage. I have done this for three 2001 and one 2002. At least two had pcb damage to traces.

Mine look fine to me .





It even melted away CR513. Seems I was too concerned with the pre-regulator not working to notice the bigger issue. I'll do a restoration and see what can be done.

[ManateeMafia]

I have one 2001 that needs similar repair. It is sitting there waiting for me to test it. I had C117 burn through the board. I have scraped and cut out most of it and filled the hole with epoxy but I will not be surprised if it is BER.  The A/D board was also defective but was repaired so at least I have some spare parts.

Good luck with the fix.

[TiN]

ManateeMafia

2001? BER?  It's nothing after 3458A, believe or not. 
There are just few nodes going on inner layers under C117,C116, so it's reasonably easy fix even if there is a hole in PCB. Actually my calibrated "golden" 2001 is with hole on C117 and bodge-wire running other side of PCB Still works a charm after 2 years (I think, lol, did not sent it for official cal second time. Will know for sure after volt transfer ).

I did not know you had that many 2001's too.

michaeliv

I think i need to work on my 2001 repair article a bit, but here's summary for first steps for you.
Keithley transformer was tested in here, with VAC data presented. It's 3458's repair log, but just scroll down a little, you will see K2001's xfmr used for power supply tests. I have extra transformer, but not sure how viable it would be shipping to you.

see what happens on the secondary .. would this be a bad idea ?

That's a good idea, it's just 50Hz xfrmr with good shielding/low noise construction, but no magic there. If your transformer heats up, or voltages are not as on mine, than it's likely shorted internally.

Your board does not look too bad to me, should be fixable with some cleaning and care. Make sure to remove all black burnt FR4, as carbonized board is conductive! You don't want that there. Don't be afraid to scrap thru layers a bit, you can fix broken connections later with bodgewires.

[michaeliv]

michaeliv

I think i need to work on my 2001 repair article a bit, but here's summary for first steps for you.
Keithley transformer was tested in here, with VAC data presented. It's 3458's repair log, but just scroll down a little, you will see K2001's xfmr used for power supply tests. I have extra transformer, but not sure how viable it would be shipping to you.

see what happens on the secondary .. would this be a bad idea ?

That's a good idea, it's just 50Hz xfrmr with good shielding/low noise construction, but no magic there. If your transformer heats up, or voltages are not as on mine, than it's likely shorted internally.

Your board does not look too bad to me, should be fixable with some cleaning and care. Make sure to remove all black burnt FR4, as carbonized board is conductive! You don't want that there. Don't be afraid to scrap thru layers a bit, you can fix broken connections later with bodgewires.

Special thanks to you TiN for all your work on this - I would be lost without it.
I did connect the White-Black to 120VAc and the transformer started drawing 150W from the mains (with no load on it) and I quickly pulled the plug. It heated up by 15C in just 2-3 seconds.
I will inquire with tek if it is possible to get a replacement transformer.

According to https://xdevs.com/doc/HP_Agilent_Keysight/3458A/img/a4_keitr_1.jpg
Red-Red/White-Red is 0-16VAC-32VAC and Violet-Violet is 0-7.1VAC.
I haven't managed to find what voltage is in between BLUE-BLUE.

Would it be possible to feed in DC voltages to the header where the transformer secondary connects in order to test the meter ? Looking at the schematics there are no obvious problems. I don't think I even need the caps to do it(though the voltage regs may require the output caps to be happy). Thoughts ?
Also I understand that CR513 is a BAV103 (missing, blown off, from my board) - Could I just put in a 1N4007 instead until replacement parts arrive ?

Thanks!

[ManateeMafia]

Yeah I have a little Keithley fan club going on here too. 

The 2001 is a good bench meter once all self tests are passing. Unless a graphic lcd is needed, it is one of the best used bench meters available. Having the full service manuals is also a plus.

[michaeliv]

While I was waiting for parts to fix my 2001 I decided to try and bleach the front face of the instrument with I think good results.
The procedure is simple : Apply hydrogen peroxide + UV to the yellow plastic.
For UV I think the sun works best - It should be done in a few hours with 12% peroxide, but there's no sun here at this time of year. Best I had was 100x5mm UV leds(395nm) that I used.
For peroxide - I used hair developer cream 40 volume (12% peroxide) - easiest to obtain.
Other options for peroxide:
- 3% liquid peroxide ~50c/L - found at any supermarket --- this however might take a LONG time and results might not be optimal
- 12%(40Vol) or 15%(50Vol) Hair developer cream (recommended) - You can find it at beauty salon shops for around $3-$5 -- You will probably need 4oz -- 16oz to be safe. The advantage of the cream is that you can apply only where needed so you don't have to remove the metal input jacks to dip the entire face in peroxide.  http://www.ebay.com/itm/-/161694949754
- 35% hydrogen peroxide teeth whitening gel (make sure it's not carbamide peroxide) - http://www.aliexpress.com/item/-/32393540490.html
- 35% hydrogen peroxide liquid - http://www.ebay.com/itm/-/311387951479

I also found a YouTube video describing the procedure: youtube.com/watch?v=9hRI6b-49Pw

[McBryce]

Nice results.

In the retro computer scene there's a huge community of people that are regularly doing this on old Amigas, Commodores and other beige / white computers. They call it "Retrobrite" (Retrobriting). You'll find loads of tips / do's / don't from them. Checkout the site Amibay.com.

McBryce.

[saturnin]

@michaeliv

One of my Keithley DMM has yellow front panel too, so I am thinking of renew it. I would also use UV leds. Please, what was exposition time in your case? Thanks.

[michaeliv]

One of my Keithley DMM has yellow front panel too, so I am thinking of renew it. I would also use UV leds. Please, what was exposition time in your case? Thanks.

In my case (100 UV LED's @ 30ma each + 12% gel peroxide) I exposed basically each side(5 sides total) for about one night (12 hours). I did each side at a time because the LED's are directional and because the gel is not dense enough to stick if not supported directly against gravity.
One thing I would like to mention is that UV seems very important - I did spot tests without UV and the bleaching was 10 times less intense.
Also don't scrub the instrument face with anything -- bleaching won't affect the painted text (Power/Range/Display ... etc.) but scrubbing will.

[Muxr]

Nice results.

In the retro computer scene there's a huge community of people that regularly doing this on old Amigas, Commodores and other beige / white computers. They call it "Retrobrite" (Retrobriting). You'll find loads of tips / do's / don't from them. Checkout the site Amibay.com.

McBryce.

Yup, I was looking at doing this to some of my gear. But I was sad to learn though that the plastic goes back to its original form after a short while.

[michaeliv]

Yup, I was looking at doing this to some of my gear. But I was sad to learn though that the plastic goes back to its original form after a short while.

Yes, I've also seen some info that the yellowing will be accelerated now. Not sure how true / universal the info is. But still even if what took originally 20 years to happen will now happen in 2-5 years, that's pretty good considering that if I had sunlight I think I could have done this in 10 min + a few hours wait, without even taking the instrument apart.

[pelule]

It may help to use ARMOR ALL as fnish and protection.

PeLUle

[McBryce]

Yup, I was looking at doing this to some of my gear. But I was sad to learn though that the plastic goes back to its original form after a short while.

Yes, my experience is that it lasts about 4 years before it's back to yellow. Some people claim that coating it with a UV blocking laquer slows this down, but that's not my experience and the people in the know (my sister is a doctor of chemistry) says that the UV blocker would have absolutely no effect on the process.

McBryce.

[saturnin]

Well, if it lasts ~4 years until it gets back to yellow, it is not so bad (at least for me).

@ michaeliv: thank you for your very informative feedback!

[michaeliv]

After installing a new transformer donated by the very generous TiN, replacing the caps and replacing the burnt 470R input resistor, my 2001 booted right up with only 6 self-test errors which I'll try to fix.
105.2 - System trigger bus -- Probably burnt MOSFET or hopefully not 5064 ASIC.
302.2 - Ohms Protect
304.6 - Ohms sources; 70nA and 770nA - Probably contaminated PCB
304.7 - Ohms sources; 4.4nA and 770nA - Probably contaminated PCB
305.2 - Test 305.2 – Input divider; divide by 100
307.3 -  Cal divider; A/D mux/buffer (x-0.5)

I also try to increase the brightness of the VFD with not so good results - the display got even dimmer.
I probably got over-zealous with the heating -- I heated up the filaments to low-medium red hot for about 30 sec then medium-high red hot for another 30-40 sec.
The filaments were not visibly physically damaged, their cold impedance is the same as before (6.8R) and the signal applied to them is the same (5v AC, waveform attached).
Any idea what happened to them and maybe of a way to undo it ?

The display is actually dimmer than it appears in the photos -- if looking at the before shot you would think the display is totally OK, however, while it was usable, it was certainly dim.

[TiN]

Glad that package arrived ok.
I see cap on mains side in not replaced? Replace them all

304.6 and 304.7 are likely due to dirty PCB or front/rear switch. We talking nanoamps there, so area around ohms muxes (two DIPs near LTC1043) must be cleaned very well for that.

105.2 - probably some resistor knocked off on digital board.

VFD - wow, that's bad. Unexpected. Perhaps you can share which currents did you run thru for more details? Also did you check your high voltage DC-DC output, to make sure you getting +55V or so?
In worst case you looking for 50-150$ for Keithley 7001 to donor VFD....

Also don't run it for too long without chassis, as big MOSFET at mains circuit, LDO on digital board are using chassis as heatsink. Without chassis, with boards laying around those will get very hot within minute.

[plesa]

Damage of VFD is strange. On single line instruments I saw big differences between the filaments. On some instruments are filaments orange and shining ( in dark room and with DISP:OFF) and on other are almost invisible. The VFD brightness seems to be same.

For 7001 I paid 35 USD and it was brand new with protective foil still in place:)
Try to ask Keithley/Tektronix for replacement part only ( DD-51C ). Smith mentioned that Keithley/Tekronix response time, so be patient.
We were discussing the displays in Electrometer thread
https://www.eevblog.com/forum/repair/electrometer-output-stage-keithley-6517

[michaeliv]

From what I recall the "high" current that I applied for 30-40 sec was 550ma @ 22.5v. See picture for how the filament looked at that load.
From what I read online the filament is coated with a film of good oxides which I might have evaporated away. It's these oxides that have the property of emitting electrons when heated up.
Also the DC-DC output is 56.3, same as before the "rejuvenation".
Funny enough for me it's not the power MOSFET that's getting hot when running without the heatsink -- it's getting to around 64C. But the voltage regulator on the digital board is getting to around 107-117C.
The capacitor near the preregulator has also been replaced -- It's just a different color than the rest.

"[...] The filament consists of a very thin tungsten wire coated with barium, strontium and calcium oxides [...]"
"[...] the lifetime of a VFD is dictated by the extent of evaporation of oxide materials coated onto the tungsten filament wires [...]"

I'll be getting a unit from which I can transplant the VFD. plesa where did you get yours -- was it eBay or somewhere else they can be found for cheap ?

[TiN]

That's likely way too strong you had it there.

[plesa]

I'll be getting a unit from which I can transplant the VFD. plesa where did you get yours -- was it eBay or somewhere else they can be found for cheap ?

My unit is from ebay, I found it and send offer which was accepted.
The damage of the VFD you have can be explained by evaporating thin layer on tungsteen wire. By this you needs higher energy to generate electron (work function).
Maybe you can try to heat filament for longer time to make brightness consistent and after that increase  bias voltage ( acceleration voltage ).
But I'm not sure how long it will last. Try to contact Keithley and ask for new VFD.

The problem of overheating voltage regulators is the same on 2002  ( 5V stabilizator has without airflow and cover 90°C 0.

[michaeliv]

105.2 - probably some resistor knocked off on digital board.

This is exactly what this was. Took me a while to realize that it was knocked off of the bottom side of the board.
My front/rear switch does not latch all the time -- I remember you mentioning that it is possible to disassemble & clean -- any tips on this ?

VFD - I have a Keithley 7002 heading my way that I will use as a donor. Tektronix gave me a quote of $417 for the display board( display by itself is not available ). Add shipping and perhaps tax. I haven't done anything to the damaged VFD because I wanted to avoid destroying it completely so I would be able to continue troubleshooting. I will try to re-heat it after I receive the 7002.

All other errors(105.2 302.2 304.6 304.7 305.2 307.3) - These were caused by a faulty R394. R394 is a 100k / 9.9M divider resistor. The 9.9M was reading infinite. I replaced that leg with a 10M that reads 9.9M. With this fix I get no errors - all tests pass. The 10M resistor has a ppm of about 1500. If I heat it up even 5C I start getting 304.7 errors (Ohms sources; 4.4nA and 770nA).

Anyone know what is the exact purpose of this divider(what measurements/ranges does it come into effect) ? I'm guessing high voltage measurements ?
It seems to be a Keithley custom part(Anyone know more ? Pic attached) . I will ask if they have it available.  Perhaps someone has a for-parts analog board and want to sell the resistor ?
Found a similar one on DigiKey but not sure if the performance matches -- http://www.digikey.com/product-detail/en/HVD5-B10M-050-05/HVD5-B10M-050-05-ND/2929140

[TiN]

Yes, that Caddock will be fine replacement. It's high voltage divider for DCV/ACV 200V and KV ranges, and probably high ohms (used as current divider). On newer units this HV divider is already formed with two Caddock's glued together for matching tempco.

Happy to hear overall progress, now should be easy to get all sorted out.

7002 is a big beast, do you plan on it's teardown? Will be interesting, as I never saw one inside. It can make a good chassis for other DIY projects

With switch it's all straightforward. Desolder it from board, remove front lock spring, slider switch rod out. Make note on direction of metal contact elements. Do NOT put them opposite side, or they will stuck inside! If its not loking it may be lost springy things at front. Then you may want new switch. They should be available from Tek.

[michaeliv]

Do you happen to know the manufacturer part numbers for the new Caddock resistors used for HV divider ? I'm interested if they're the same resistance (100k/9.9M) or just the same ratio 1:100.
Sure, I'll do a teardown and upload pics to your ftp.

[TiN]

You can see photos of them in Model 2001M review and Model 2002. I'm 99.9% sure they are same 100k/9.9M, but did not measure.

[TiN]

Let's fix another 2001...



This one have 4xx self-test issues after capacitor replacement and PCB cleanup...