Restoration glory of Keithley 2001 DMM

[TiN]

Meter reports errors 401.1, 402.1, 404.1,2,3,4,5, 405.2,4,6,8, 406.6, 407.1,2,3 , 409.6, 410.1, 411.1,2.
If switch to ACV or ACI mode it just shows 470VAC or overflow, and DCI current on 200mA,20mA,2mA,200uA is overflow too.

If I remove Q516 transistor which routes ACV stuff thru U526 mux into measurement front end - I can see some right-ish readings on DCI, so something is going on on AC-side.

[michaeliv]

I'm trying to swap the VFD of the Keithley 2001 with a compatible one from a different board. I'm having quite a bit of difficulty removing the VFD from the board. Anyone who has done this successfully -- any tips on how to go about it ? The problem is that there are lots of pins which are soldered all the way through the 1.6mm PCB. The pins are about the same diameter as the hole they plug into -- so not much wiggle room. Any tips on desoldering the VFD ? I basically only have access to one side of the PCB so it doesn't look like I can use solder wick.

[TiN]

Solder wick and lots of patience is the way I went with my 2400 repair. Add lots of flux, remove solder with wick, and then wiggle pin till it's free. If you have large enough solder bath large enough you can reflow whole row as well, but I don't have such things, so I went with wick and wiggle.

It took me about an 1.5 hours to get display free from PCB, so patience is a key.

[JoeO]

I'm trying to swap the VFD of the Keithley 2001 with a compatible one from a different board. I'm having quite a bit of difficulty removing the VFD from the board. Anyone who has done this successfully -- any tips on how to go about it ? The problem is that there are lots of pins which are soldered all the way through the 1.6mm PCB. The pins are about the same diameter as the hole they plug into -- so not much wiggle room. Any tips on desoldering the VFD ? I basically only have access to one side of the PCB so it doesn't look like I can use solder wick.

ISJ has a video about how he did it.

[plesa]

Use solder extract tool (vacuum one) and make rotation movement during sucking solder. This should free almost all pins.If not, repeat it. After that use heat gun to heat up the double side tape and peel the display carefully.

Or ask nearest repair center, for them it is piece of cake.
What did you use as VFD donor? 7001?

[michaeliv]

ISJ has a video about how he did it.

The 2015 in the Youtube video is not nearly as hard enough to desolder as the 2001. Mainly because the pins are spaced much farther apart and they have lots of wiggle room in the through-holes -- compared to the 2001 which are a very snug fit.

What did you use as VFD donor? 7001?

I used a 7002 as a donor -- the one from here: https://www.eevblog.com/forum/testgear/keithley-7002-switch-system-teardown/
I actually tried with 2 solder extract vacuum guns but the pins are so close together that I couldn't generate a good contact so I couldn't easily melt the solder or if I did manage to I couldn't create a seal in order to suck out the solder. I imagine it should be doable with the adequate tip for the solder sucker - but I don't have one and I think they don't make tips that narrow.
BTW no need to heat the board to detach. It's very easy to cut / detach the tape with a box cutter. Took me 5 seconds with a sharp cutter.

In my attempts I manage to over-heat the pins and they're not making consistent contact with the VFD glass-printed metal any more ... so I'll be trying it again with a new VFD board. I also bent up the VFD from the board which turns out is a big no-no and may have added / caused some pins to not make contact.
The good news is that I was able to experiment some more with reviving the VFD(that's how my original VFD got damaged, by applying too much voltage/current in trying to revive it).
From new experiments 15V for 2-3 seconds would be ideal for this type of VFD. I did get a decent bump in brightness by doing so.
VFD damage(it actually got dimmer) started to occur once I got to 22-23 V, even for only 2 seconds.

[TiN]

Meanwhile I got some progress on redrawing schematics of 2001, as I cannot follow what goes where on vendors schematic.
Draft as of today:



I need another lifetime to understand everything in there completely though. 

[pelule]

If you don't need the old VFD anymore, the secures method is, to cut the leads to remove the old gals first.
Reduces the thermal capacity of the leads und allows easier unsolding.
We did it in that ways when I was working for a Japanese VFD company...
BR
PeLuLe

[Macbeth]

I don't see what the problem is with these VFDs. Every VCR back in the '90s had a similar display and I replaced plenty with nothing more than a handheld solder sucker (ORYX was the best IMHO) and a regular Iron (Weller it has to be said, but a good old mains power Antex was no problem)

Of course the unleaded crap wasn't around then, but you can always just pre-solder with leaded, Chip-Quik or flux. Really though, two layer is nothing to deal with. It's the multi layer boards are kryptonite!

[TiN]

Fixed my third 2001. Problem was bad chopper LTC1050 with 145 ohm from -V to +V, which caused floating supply from +38/-38V booster to get screwed.
VR502,VR504 and Q543 were checked and found OK. VR504 was bit off, so i replaced it with new 4.4V zener.
After replacement of LTC1050 meter passed all self-test steps and both ACV,DCI,ACI working like a charm now.



Now one more 2001 left to fix, on which issue is already likely narrowed down to LT1223, but I need get replacement part next week to continue troubleshooting.
I'll post my redrawn schematics once all checked and cleaned up.

[TiN]

One more thing, I was always curious how Keithley able to deliver those ACV specs using just a AD637JR. Answer is here in this US patent. They use standalone full-wave rectifier with crest factor detector and lot of balancing around R530 to improve accuracy ~20 times and extend frequency range of TrueRMS converter, using some smart analog voodoo.

Obviously, Keithley 2002 is exactly same in this respect as ACV/ACI is 100% copy of 2001's circuit for it.

[ManateeMafia]

You are running out of broken meters! What's next?

[TiN]

Perhaps K2000. I stolen few DG211's from there today..

[ManateeMafia]

Great job on repair. Hopefully broken ones don't go up in price now. The empty 3458A's are selling too high already....

[macboy]

One more thing, I was always curious how Keithley able to deliver those ACV specs using just a AD637JR. Answer is here in this US patent. They use standalone full-wave rectifier with crest factor detector and lot of balancing around R530 to improve accuracy ~20 times and extend frequency range of TrueRMS converter, using some smart analog voodoo.

Obviously, Keithley 2002 is exactly same in this respect as ACV/ACI is 100% copy of 2001's circuit for it.

Fascinating.

Good job on another repair, another top notch meter saved from scrap and ready to get to work.  I am really looking forward to your redrawn schematics as I too have a hard time following the seemingly randomly chopped up multi page schematics from Keithley. (Not that we can complain about just having factory schematics at all!).

As for my own, I did repair my one faulty 2001 by simply replacing all the electrolytic caps. None of the originals had leaked, and all measured at a sensible capacitance but had maybe 3 to 5 times the ESR of the new ones. Maybe that was the issue? I also touched up dodgy looking soldering on a bridge rectifier. Maybe that did it. In any case it is back on duty now alongside its three friends.

[TiN]

Assembled unit, now it's ready for some tests .

Here are some photos for you, precision gear fanboys.



Boards in place:



Digital board is the only one I have with dual ROMs. I pimped it up with fresh capacitors, latest firmware 2001-M B17 and MEM2 option with knockoff Dallas (not dead yet). Note on photo incorrect dallas position, should be rotated 180° .



First self-test after assembly.



All pass with flying colors. Calibrated it quickly with 2V,20V,20KOhm,1MOhm, measured 10V off my 3245A.

One thing I found interesting in 2001M B17 f/w is presence of extra config option for DCV : Analog filter.
url]


2001M's user menu says:

The Model 2001 has an analog filter for use with the DCV function. This filter reduces the number of overflow errors caused by noise seen on the input signal. The analog filter is most effective when measuring voltages greater than 2 Vp-p frequencies ranging from 10kHz to 1MHz.

The analog filter is a single stage, single-pole, low-pass RC network that rolls off the signal at an approximate rate of 20dB per decade above the cutoff frequency of 10kHz. The analog filter has a zero at 600kHz. Figure 3-41, part B shows the general frequency response for the analog filter.

The analog filter is most effective on the 2V or 20V range with line synchronization enabled. On the 200mV range, a noisy input signal may cause overflow readings even though the analog filter is enabled.

I wonder if it should be somewhere on analog board, as my analog board is Rev.J, definately not real 2001M's Rev.R. Perhaps I should take my googles and look on photos for extra resistor and capacitor, compared to my analog PCB.

Since these last units were bought as scrap long ago, I don't have black shield cover. Anyone have 2 for sale? Also need bottom part. I bodged paper "air tunnel wall" around power parts to direct most of airflow to exhaust on side, just like stock K2001 does. Seems some of air still go elsewhere, as with DCV measuring 10V even with filter readings jump ~75uV (other 2001, with native cover stays ~10uV stable).

[macboy]

Interesting that you haven't seen the analog filter before. All four of mine have the analog filter, they range from firmware A06 to B15. I think I had posted the analog board revisions in this thread long ago.

[TiN]

I think A06 dont have that, as mine A08 does not have it either too.
I'm sure It's only B-version feature, and B10 don't have it (no text strings in firmware binary), but B15 does have. If it's analog, then there should be hardware somewhere for it.

[macboy]

I think A06 dont have that, as mine A08 does not have it either too.
I'm sure It's only B-version feature, and B10 don't have it (no text strings in firmware binary), but B15 does have. If it's analog, then there should be hardware somewhere for it.

I stand corrected. My A06 version does not have the analog filter.
My B10 had been upgraded to B17, so I downgraded it again (with original ROMs) and checked... it does have the analog filter with B10. The analog board is 2001-012-04N. I checked the firmware dumps of those B10 ROMs and I do see the strings "AAO ITR" in one and "NLGFLE" in the other, which combine to make "ANALOG FILTER". As a sanity check, I downloaded the B10 firmware from your server and the files are identical to my own.

[michaeliv]

Got myself a new 7001 to pull the display from and put it in my 2001. As expected the display is not like new and could use some brightening up. I was thinking to increase the runtime current through the filament. However, the filament seems to be driven directly by a winding on the DC-DC converter that also generates the 55V for the VFD.
Any bright ideas on how to get a 6-7V peek-to-peek to apply to the VFD filament?

Thanks!

[TiN]

Is your DC-DC open board, or molded epoxied box?

[michaeliv]

Is your DC-DC open board, or molded epoxied box?

It is the open board type, identical to the one in the 7002:

[TiN]

Here's schematics of it which I reversed a year ago.



Perhaps try on bad VFD first and reduce R102/R101 a bit, to see if higher current can be delivered. Check output voltages during this.

[michaeliv]

Here's schematics of it which I reversed a year ago.



Perhaps try on bad VFD first and reduce R102/R101 a bit, to see if higher current can be delivered. Check output voltages during this.

Thanks for the suggestion, but I had no luck with this, unfortunately.

[kada]

Hello Keithley fans! 

I got my first 2001 (actually 2001M) #1 a one year ago. It mentioned in this thread. It is working properly and regarding to calibration date string it was calibrated in 2012.

I also got another one 2001 #2 not working from eBay without cover and board shield.
Analog board revision K. Digital board revision J. ADC board revision G. Firmware version A06.



Desolder caps and see familiar picture:



Board washing/cleaning:



New caps soldered (thanks to TiN  ):



Replaced leaked 1000 uF caps on the digital board with new 2200 uF as well.

Also some retrobright experiments:



...and result:


After power on the VFD does not display anything. The problem was in burned DC/DC converter on the digital board.
After replacing (taken from 7001) the VFD start working. Multimeter operates good except some errors:

200.1   A/D Zero
200.6   x0.02 Line Cycle Integration
200.7   x0.01 Line Cycle Integration
201.2   7V Reference

SKE encountered with the same errors:

Self test reported these error codes:
200.1   A/D Zero
200.6   x0.02 Line Cycle Integration
200.7   x0.01 Line Cycle Integration
201.2   7V Reference

Did you find a solution?

What I tried to do to localize the problem:
1. Insert ADC board from my working 2001M #1 to #2 - same errors 200.1, 200.6, 200.7, 201.2
2. Insert ADC board from #2 to 2001M #1 - no errors
3. Insert digital board from 2001M #1 to #2 - no errors!
4. Insert digital board from #2 to 2001M #1 - same errors 200.1, 200.6, 200.7, 201.2

Looks like the problem is defective digital board. In the meanwhile I can do all measurements with unit #2 without problems. So the analog <-> digital board communication works properly.
I also expected damaged EEPROM and tried to load various images to EEPROM which TiN posted without luck.

Are there any thoughts?
Thanks,
Andrey.