Restoration glory of Keithley 2001 DMM

[plesa]

Wow pimped K2001, good start!! What about putting the ADC board on andle connector and soldering LTZ1000 board directly to analog board and isolate it from outside world.
Based on my experience with LM399 it is too sensitive to outside world. Only the metal case and insulation reduced it to acceptable level.

[saturnin]

@ManateeMafia

Actually, during further investigation I found out that I get 200.1 and 200.3 errors too (but not always - they are rarer than 200.2 error). Moreover, it is much more probable that I get these errors when I run test in "step" mode than in "continuous" mode. Strange...

I also made a comparison of my KEI2001 and KEI2000. I measured a stable 10V reference output:

-> KEI2000 (10V, MEDIUM speed = 1NPLC, no filter, 1000 samples)
average value: 10.04788 V
std dev.: 2.08 uV
min. / max. reading: 10.04787 V / 10.04788 V

-> KEI2001 (20V, 1NPLC, line sync, synchronous autozero, no filter, 404 samples)
average value: 10.048091 V
std. dev.: 7.86 uV
min. / max. reading: 10.04807 V / 10.04811 V

I also measured all supply voltages. They are in tolerance and without any unusual noise. The main +7V reference is stable too. Then, I checked reference signals in A/D converter circuit:

DC measurements with my KEI2000, same config as above:
Vref 6.4V : 6.22416 V, std. dev.: 2.28 uV
+Vref +10.25V : 10.26373 V, std. dev.: 9.59 uV
-Vref -10.25V: -10.26004 V, std. dev.: 25.92 uV (quite high noise, IMO)

When A/D converter is disabled, i.e. it is not measuring, local reference voltages are much more stable:
+Vref +10.25V : 10.26370 V, std. dev. 2.56 uV
-Vref -10.25V : -10.25980 V, std. dev. 1.00 uV

With my scope, I measured several signals in A/D converter. They seem to be ok, except one suspicious - a control signal at gate of Q807. It is a square signal with levels 0V / -15V. I zoomed at its 0V level and I can see there is a overshoot to positive values (as high as ~300 mV, see attached pictures), which could be quite enough to inject some noise current to integrator's input (because a diode in the jfet would be forward biased). My reference ground for this measurement was "signal common" (1). I wonder if this could be an error or not...?

[ManateeMafia]

@saturnin

I have looked at the gate of Q807, and zoomed in to the signal with a Fluke 199C. I do not see the overshoot that you have posted.

[TiN]

Q807 is nice and clean here too, measured with CSA7404 + P6245 probe.



Back to LTZ-mod. Separated heater supply from LTZ module to take power directly from analog board +15V node near LDO.
Will run longer term test next days.

[saturnin]

ManateeMafia, TiN,

thanks for your measurements and confirmation the signal is clean in your cases. I will continue with debugging...

Btw. TiN, I noticed your scope showed 10.47V p-p, but it should be 15V p-p, since Q807 gate is connected to U807, which is a comparator with open collector. Therefore its high state should be 0V and low state -15V, since its gnd (terminal 12) is connected to -15V. Did you really measure signal across R859?

[TiN]

Dynamic range of P6245 probe is +/- 8V only, so it's capped by probe, that's why 10.47V.
I forgot my TCA-1MEG buffer at work, so that's why it was not measured properly. 
I don't have any other "easier" scope.

[bson]

Hi guys.  My Keithley 2001 has B13 firmware and I'm looking to upgrade it.  Correct me if I'm wrong, but to upgrade it I download the odd/even banks (thanks TIN!!!), program a pair of 27C040s (I got Winbond W27E040 EEPROMs, -12 while the stock EPROMs appear to be -15) and replace the stock ROMs?  Or I might use ATMEL '040 OTPs, which I assume are just EPROMs without a window.   Will the instrument require recalibration (i.e. is the calibration data firmware specific)?  It's due for a calibration anyway, so no big deal.

Looking at the 68302 freescale data sheet for the bus timing combined with the 7.68MHz clock, it seems to me ROM speed is completely irrelevant, and even a 250ns read time should work just fine...

[TiN]

Hi bson,

Welcome. Do you mind to upload your B13 firmware and EEPROM dumps perhaps to my collection? You can use my FTP for that.
You can use latest B17 2001-M firmware with your dual-ROM 2001.

Also if you can take few photos of internals both analog, ADC and digital boards, would be great addition as well, seems your units is recent is you have EEPROMs there.

Regarding your questions, yes, it does not matter which ROM speedgrade you use, it's all slow and nice. And for recalibration, so far I'm not aware of any 2001 version changes which would need recalibration (except perhaps going from B-version to A-version firmware, but that's not your case anyway). I upgraded my original B08 to B15 and now B17 2001-M, calibration still no change, based on measurements with 2V, 10VDC, 1Meg, 10K, 19K, 190R resistors, etc.

[TheSteve]

This is a great thread - and probably extremely useful as I received a 2001 today. It has B09 firmware and needs a little TLC.
It has the following errors in diagnostics:

407.1 Front end
407.2 Front end
407.3 Front end
409.6 /500 Freq Comp
410.1 TRMS
411.1 TRMS
411.2 TRMS

I haven't opened it up but am told it has had the common bad capacitors replaced already.

Another fun project for the bench.

[dadler]

Do the caps in the 2000/2015 models similarly die and eat pcb traces, or is this a problem that occurs more frequently in the 2001 models?

The caps in my 2015 (I think it was manufactured in 2002/2003?) look ok to me, but I'll swap them if this is just a headache waiting to happen.

[McBryce]

Do the caps in the 2000/2015 models similarly die and eat pcb traces, or is this a problem that occurs more frequently in the 2001 models?

The caps in my 2015 (I think it was manufactured in 2002/2003?) look ok to me, but I'll swap them if this is just a headache waiting to happen.

It's not just common to 2000/2015 and 2001 models, it's common to anything that has electrolytic capacitors in it. Although obviously a device from Keithley will have used better quality caps than some cjheap Chinese device, so they should last longer. The question with caps is never "if" but "when".

McBryce.

[TiN]

This is a great thread - and probably extremely useful as I received a 2001 today. It has B09 firmware and needs a little TLC.
It has the following errors in diagnostics:

I haven't opened it up but am told it has had the common bad capacitors replaced already.

Welcome.

Don't forget to upload your B09 firmware into our humble collection. Also pics would be nice addition as well.
Replace caps asap unless your unit is 2010+ year (can tell from date codes on ICs). Caps are prone to leak and cause disasters because on 2001/2002 they are located in worst spot possible, just near hot regulators, transformer and getting cooked with temps over 60°C 24/7, still being under high voltage applied.
Most of 4xx series errors are due issues with bootstrap circuitry as well. In case you missed, i have this little summary of issues in few of my 2001's.

Replace caps on digital board too.

[McBryce]

2010+ ? Is that not being a bit over cautious? My Keithley 2000 is from 2005, but looks like it was rarely used. I opened it up and the caps look like new. Pulled one and checked capacitance and ESR which were also both well within tolerance.

McBryce.

[TiN]

Better be safe than sorry. Also 2001 is very different beast, compared to 2000 (which does not have bootstrap block with leaking capacitors).

[TheSteve]

This is a great thread - and probably extremely useful as I received a 2001 today. It has B09 firmware and needs a little TLC.
It has the following errors in diagnostics:

I haven't opened it up but am told it has had the common bad capacitors replaced already.

Welcome.

Don't forget to upload your B09 firmware into our humble collection. Also pics would be nice addition as well.
Replace caps asap unless your unit is 2010+ year (can tell from date codes on ICs). Caps are prone to leak and cause disasters because on 2001/2002 they are located in worst spot possible, just near hot regulators, transformer and getting cooked with temps over 60°C 24/7, still being under high voltage applied.
Most of 4xx series errors are due issues with bootstrap circuitry as well. In case you missed, i have this little summary of issues in few of my 2001's.

Replace caps on digital board too.

Thank you for the advice.

I was going to read the eproms but my reader/writer is just too vintage for a 27c4001, lol. I will visit a friend or buy something newer in the near future to get a dump for the group.
I see many of the caps of have been replaced in my unit and there was clearly some damage from the previous bad caps. I have attaching two pics of how I received it. One shows the area near the bad caps, the second shows Q339 and Q340(is this normal?). I checked and BS+ and BS- actually look fine on the scope and show the proper voltage. However +8VF varies between 5.8 and 6.2 volts. All of the other voltages look fine. I think I will order all new caps even if some have been replaced and I will replace the missing diode(s). Any thoughts on other parts I might want to order at the same time?

[TiN]

Ouch... Get all electrolytes (both digital board and analog) for replacement (your unit made in 1994).
CR513,CR514 are BAV103 in SOD80.
Bodgery around Q340 is NOT normal. I'd buy bunch of LM339, cheap digital logic, MC14094s, DG211's, 74HC00A and just replace those guys as well.
Highly suggest desolder U507,U508,U509, clean everything around there with clean alcohol very well, solder unobtanium U509 back, replace rest.

[TheSteve]

Ouch... Get all electrolytes (both digital board and analog) for replacement (your unit made in 1994).
CR513,CR514 are BAV103 in SOD80.
Bodgery around Q340 is NOT normal. I'd buy bunch of LM339, cheap digital logic, MC14094s, DG211's, 74HC00A and just replace those guys as well.
Highly suggest desolder U507,U508,U509, clean everything around there with clean alcohol very well, solder unobtanium U509 back, replace rest.

I replaced all of the caps on both analog and digital boards last night. I also installed the proper missing diodes and gave the board a good cleaning. This didn't change any of the faults but at least it has the correct parts everywhere now. The weird bodges around Q340 seem to match up with the schematic and the solder connections look original. I'll have another look this weekend but perhaps it was a short run with a bad PCB design.
I didn't replace any of the chips near U507/508/509 as the board was very clean in that area and doesn't show any indication of having had capacitor leakage on it. I will dig into the diagnostics this weekend and hopefully track down the bad component that is causing my faults - if anyone has any guesses let me know and I'll start the trouble shooting there.

My faults are:
407.1 Front end
407.2 Front end
407.3 Front end
409.6 /500 Freq Comp(this one may not occur 100% of the time)
410.1 TRMS
411.1 TRMS
411.2 TRMS

[TiN]

Well, bear in mind, that on two units with same faults I spent days finding fault but could not isolate any. After desoldering those chips, cleaning and putting them back - all errors were gone.

[TheSteve]

I am pleased to report my Keithley 2001 is now error free and working great!

The failed component was Q547 - it wasn't totally open but but didn't turn on properly so relay K503 never closed.
I didn't remove any of the other IC's  as they all looked very clean and didn't appear to have suffered any contamination.
Just to have it all in the same post the faults I was seeing were:
407.1 Front end
407.2 Front end
407.3 Front end
409.6 /500 Freq Comp(this one may not occur 100% of the time)
410.1 TRMS
411.1 TRMS
411.2 TRMS

When I swapped the caps C116 and C117 they were changed to 50 volts(as previously mentioned in this thread they should never have been spec'd at 35 volts).

Having the schematics made all the difference - I can't believe you guys slogged through this thing without them originally, especially being the PCB layout is not very refined.

I still plan to dump my firmware and calibration eeprom next time I visit a buddy with a programmer and will upload them. I guess I may as well convert it to a MEMS version at the same time.

[ManateeMafia]

Great work. These are wonderful meters and it should give you many years of use. It will be tempting to throw it in 8.5 digit mode now.

[TheSteve]

Indeed, I went into the special menu and then enabled 8.5 digit mode just to see all those numbers!

[bson]

FINALLY received my EEPROMs from China!  I'm now the happy owner of a B17 2001M! 
Uploaded the B13 firmware.  That was a little tricky - one EPROM was a national semidestructor and was easy enough to read, but the other was an ST device I couldn't get to the part number on; too much hardened sticker residue.  Instead of destroying the sticker with something nasty I tried all the various ST EPROMs, turns out it was a 27C4001.  Go figure.  The TL866A wouldn't read it unless I got it right, which is a bit silly...  Oh, and I couldn't use use my trusty old Xeltek programmer either... no more parports!!! 

Now I'm just waiting for my DS1245YK NVRAM (MEM2) to arrive so I can initialize it with my S/N, pop it into the socket and close this bugger back up!   

[TheSteve]

I will be doing the same when the programmer and DS1245Y I ordered arrives(probably a month from china). I will upgrade to B17 2001M MEMS2. I also noticed a 2001 with B17 firmware on ebay(no M) - item # 161779473828 for pics.

[bson]

Ooh, it'll be interesting to see how much the ROM dumps differ between the B17 2001/2001M...

It seems the 2001M has an extra ACV mode (average-responding ACV with calculated RMS) to make it an upgrade path from the 175-AV, for automated test systems.  Basically it's an averaging mode reported as RMS.  I bet this is all firmware.  Not much use for it with true RMS, other than for readout compatibility with older pre-TRMS setups.
http://www.keithley.com/data?asset=14876

[TiN]

Thanks for firmware, added to collection and document page.

I have teardown article almost ready about 2001M, just need translate it and readproof it.