This Keithley 2001 IS NOW saved!

[Kleinstein]

If the signals are all DC, U514 is not working normal.
The current through R436 is rather high and there must be a way for it to go - looks like some path not intended: U514 is the main candidate, U515 is possible too.  Q546 could be the culprit too though unlikely to be partially broken and the gate driver must be strong to still get 4.95 V.

[Zucca]

Yes all DC in Volts.
U514 is already been shipped to me. U515 was replaced before.

Funny thing it was the last AD847JR in stock at TME. After my order stock TME=0 Unit. 

Another gossip is that U514 started up either generating an always positive -COMP signal or a always negative one (maybe the nature of a sick unit in a positive feedback). That's why I was getting either one set of errors or the other one.   

[Kleinstein]

For a fist test one could try a more normal, slower OP for U514 (e.g. LM318, maybe LF356 or similar). Chances are one would install a socket for the suspect OP anyway.

A broken (conducting)  Q542 could also cause the comparator to stay at it's state, as the hysteresis would than be quite large. However it can not explain the high current through R436  (unless R436 is broken). One could measure the other side of R279 and this way check if U515 is the culprit.
With the positive voltage at the inverting input the AD847 should normally be all the way negative, so there is something wrong with the OP (unless the circuit is oscillating).

[Zucca]

Well U514 was replaced,

Now I got:

404.1, 2
405.6, 8

there is another bastard on the board. 

EDIT: I forgot to point out that Q542 and Q546 are p-ch JFET
http://www.learningaboutelectronics.com/Articles/P-channel-JFET
http://pdf.datasheetcatalog.com/datasheet/calogic/J270.PDF

[Zucca]

Unbelievable, check out U507 [everything in VDC]:

TEST	Pin 2	Pin 3 (-COMP)	Pin 7	Pin 8
404.1	2,5m	-0,294	+0,29	+4,49
404.2	2,5m	-0,257	+0,29	+4,49
404.3	3,29m	+0,42	+0,29	+4,55
404.4	3,25m	+0,59	+0,29	+4,57
404.5	3,3m	+0,628	+0,29	+4,57

None of the circuits are oscillating. Because with the faulty U514 -COMP was always positive I could not detect that U507 was stuck and not switching.... FUUUUUUUU --> other 7€ to DHL for the next chip... 

[tagchen]

hi,  last weeks how i have some time, i begin repair two 2001.

first defect spend parts for second repair.
pcb blow up neer caps, repair pcb and caps, change relais and parts from power supply part, change all chips marked in blue!, change fan and pcb is running with many erros, but run . too many party needed so i do nothing more.

defect now :transformer frontinterface, completed frontinterface (display+chips), thermalfuse (ceramic), transformer ...
offer for new 2001 with many of discount is 2600euro, needed parts cost more!
(offer for rebuild front transformer 580euro, offer transformer 960euro, offer frontinterface 1800euro)


second repair same, blow up caps, change many of chips same other repair (blue marked), use transformer and thermalfuse from 1. (transformer positions needs new screwhole to mount, hole now left bevor in middle of transformer , change fan ...

last error, Software 1991, A06, A01:
200.1 A/D
200.6 A/D
200.7 A/D
201.2 Testcal
412.1 ACA Switch

the 200.x are errors from firmware??
i reading her https://www.eevblog.com/forum/testgear/restoration-glory-of-keithley-2001-dmm/500/
what can i do as next step??

for test i calibrated the 2001 and runs without errors. voltage and current looks like good.

[Kleinstein]

The 200.x Tests are supposed to be mainly for the ADC itself. So this may be the ADC board. With a 2nd K2001 bad at hand one could try swapping the ADC board - however only after checking the supplies, to make sure not to damage the ADC board.

[tagchen]

2nd board has the same error 200.x.
i read that the firmware A08 has not the problem with 200.x. it is? must change from A06 to A08?

https://xdevs.com/fix/kei2001/
https://www.eevblog.com/forum/testgear/restoration-glory-of-keithley-2001-dmm/

[Kjelt]

No the 200.x tests can be many things, causes. Often has nothing to do with the A/D board it self as with some of the needed signals , reference floating voltages.
I am still trying to find my cause, even have a good friend who has 20 yr repair experience on it but it is hard when the cause is not continuous.
His last thought about it is that due to the cap leakage some pcb trace inside the pcb has corroded might even make contact with other trace which influences the floating voltage reference.
Hard to find.
The meter it self is working and in calibration range on all inputs/settings, still get these weird ST errors.

 https://www.eevblog.com/forum/testgear/restoration-glory-of-keithley-2001-dmm/msg2303367/#msg2303367

[tagchen]

thanks, idea in wich part of board is to search?

[Kjelt]

Iam concentrating on the traces near the powersupplies where the caps leaked.

[Kleinstein]

thanks, idea in wich part of board is to search?

A first part could be looking for the signals that are measured in the self test. The general idea of the test is to generate a test voltage and measure than. AFAIK one can run the self tests in a kind of single step more and thus have a more static mode of operation.
So one could than follow the path of the signal and do extra measurements with a scope or DMM, e.g. at the ADC inputs, DAC to generate the signal or amplifier input. This way one can often narrow down the area where the defect is.

Different firmware version could be slightly different in the acceptable limits for the tests.

[Zucca]

AFAIK one can run the self tests in a kind of single step more and thus have a more static mode of operation.

This, that's why I am investing time and energy in this old piece of equipment. The manuals (service + schematics) are awesome and the diagnostic test steps will make easy future fixes (I hope).

[Zucca]

thermalfuse (ceramic)

So R100 is a thermalfuse and not a power resistor? I am confused.

EDIT:
Original Part is:
RES, 470, 5%, 10W, VERTICAL MOUNT Keithely Part Number R-401-470.
Made by KRL/BANTRY code R-LF3476.

I replaced it with:
https://www.tme.eu/de/en/details/hs10-470rj/10w-resistors/arcol/

[Zucca]

U507 replaced, no more errors!

[bitseeker]

That was quite the adventure. Congrats, Zucca!

[Specmaster]

Well done 

[Kjelt]

  great result.
You tortured me a bit with the jodelahi video, but I'll survive.

[Zucca]

some pcb trace inside the pcb has corroded

How about let some current flow through the suspected traces and check with your Flir E4 if there are any hot spots? If a trace is corroded R goes up ---> heat will be generated there.

[Zucca]

must change from A06 to A08?

Try to upgrade the firmware and see what happens (Not wasting time, I would do it anyway). Are both your K2001 old A-Units?

[Zucca]

Guys slowly is time to think about low prio little parts.

I would like to buy:

1) 2 Nuts and 2 washers for the rear coax
2) If the rear writings are still good maybe I could upgrade the entire metal case
3) GPIB connector screws
4) Front Bezel with oder without display-key board

see the pics below regarding 1), 2) and 3):



If anyone has something for cheap please PM me.

[tagchen]

thermalfuse (ceramic)

So R100 is a thermalfuse and not a power resistor? I am confused.

EDIT:
Original Part is:
RES, 470, 5%, 10W, VERTICAL MOUNT Keithely Part Number R-401-470.
Made by KRL/BANTRY code R-LF3476.

oh no, it is a resistor with thermalfuse. You find it in many device from HP and Agilent. Its an producer in USA, you can order it by them or keithley.

i open the ceramic resistor case and in this you find them in picture. i fixed it for testing device with new thermalfuse (red is original) and have order new in USA.

[Zucca]

Thanks now everything is cristal clear, and finally I know why R100 goes open so often.
I do not like thermalfuse, I think I will take the risk to live without it.

[Zucca]

This constant regulation of effective resistance in series with the transformer regulates the power delivered to the instrument.

Interesting, now I understood how the Pre-regulator circuit works (service manual page 2-17).
Since the previous owner moron put his dirty handy on R100, I need to check if this circuit is working since is it not tested in the self test.

Moreover I have to be carefull around R100, it is main voltage territory.

 

[Kjelt]

I am in despair, my second batch of 27C4096 eproms i ordered is also not good.
They all fail on some bits , some can't be programmed at all.

Is there a modern flash chip, pin equivalent for this chip that anyone knows or a  trustworthy source ?
I still would like to update the firmware to see if it solves my last error.