| Electronics > Repair |
| Keithley 2002 repair help |
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| nikonoid:
I am certainly not complaining. This was a great purchase. My reaction was more to a condition of the unit being an insult of a fine instrument. I like the challenge and am looking forward to restoring it, hopefully with the group's help. The help and advise I got while repairing my first K2002 was invaluable. For now my plan is this: 1) Remove analog board 2) Identify and replace burned parts and repair traces. I expect replacing bridge rectifier, diodes and caps. 3) Power up the meter and self test with analog board outside of the case 4) Address self test issues 5) Decide on overall cleaning and decontamination procedure 6) Recap, new shield, case |
| alm:
I would probably clean the board(s) after removing suspect parts, and before mounting new parts or testing. The leakage may very well mess up the self tests anyway, so I see no reason to test it before hand. It may also make it easier to see defects and nicer to work on. |
| TiN:
Yea, item number 5 should be after number 2, not the other way around. However PSU section for 2001/2002 analog domain is bit tricky, because of capacitor bootstrap doubler. That's exactly what two of the big caps near transformer are for, doubling unregulated +18/-18 to +36/-36 BS rails, which float around input to provide high impedance on main ranges. These rails power many opamps on frontend, and risk is high that one or more of those are taken out. Schematics for that part almost same as 2001. |
| nikonoid:
Thank you for suggestions. On another note, today I got a call from local calibration lab (New Jersey) telling me that my first Keithley 2002 failed the calibration. The tech said that meter was in spec everywhere but in DC Volts that were out of spec by a bit. However his attempts to calibrate it were not successful. His exact words were that "unit does not hold cal on DC Volts". He tried several calibrators but could not get new constants to store. It sounds like EEPROM problem or new constants are too much outside of normal range and firmware is refusing to use them. I will have it back on Thursday. I am considering doing a dry run calibration myself. Not that it would be a good calibration, but just to see what exactly is not working. I got calibrated K2000, EDC 520A, GenRad 1433-B for resistances and Agilent 6611C for 2 amps range. I might also consider changing calibration parameters manually though secret menu. Have you ever had a similar situation with Keithley 2001/2002? Do you have any other suggesting on what to try? Thank you. |
| Zucca:
--- Quote from: nikonoid on July 19, 2017, 05:00:20 am ---Have you ever had a similar situation with Keithley 2001/2002? Do you have any other suggesting on what to try? --- End quote --- One fo my 34401A has same issue... fully story https://www.eevblog.com/forum/repair/hp-34401a-drift-in-the-2w-r-mode-in-the-100-ohm-range/25/ At the end it was a bad cell in the EPROM that would not get written... and this drive you crazy because you triple check all the analog circuit, but in the end is a tricky digital failure. Fortunately your cal lab pointed you in the right direction, mine was just saying 2WR 100Ohm is out of spec... good luck. |
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