Electronics > Repair
Keithley 2002 repair help
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alm:
Maybe the silkscreen is wrong? Check the voltages on the pins of the 7805 and compare with the datasheet.
nikonoid:
Another update.

For power test 9 and 10, Voltage on the U105 is actually fine. Before I used a wrong point as an Isolated Common (it is not in the manual). This time using a negative leg of a bridge ratifier CR104 did the trick.

Power test 3 is actually a mistype in the repair manual (yes, another one). Sink screen is fine, but the manual was supposed to refer to Pin 1 not Pin 3 for 5V measurement on U108.

After these measurements I reran the self-test and only saw errors 306.1 and 306.2. Somehow other errors disappeared after diode change!

However this was only an open inputs test. I reconnected all the inputs and ran the full test. This time I got more variety of errors.
306.1/306.2
500.1/500.2/500.3/500.4/500.6/500.7     basically current measurements are shot
501.2
600.2

Regular spot checking of measurement functions showed that voltage works reasonably well, 2W/4W ohms work on everything but 2MOhm range, Amps do not show anything resembling input signal. It is almost like the amps path got blown somewhere. 


PS. I just realized that I forgot to recheck Power Test 4 results. This will be a task for another day.


 
TiN:
Stupid questions: Is the current fuse ok, and did you short HI input to AMPs jack before going with current test? :)
Btw, what's the FW rev?
nikonoid:
Yes, I shorted Input Hi to Amps and I did check fuses.  :-+
I also checked both front and rear connections in case of a switch problem. For the front I was shorting directly into solder pad on the board as my white wire for current is still de-soldered.

I got exactly same list of errors for front and rear connections. It sounds like some sort of protection on amps input is blown. There is also another possibility: when meter is going through tests I can hear that one of relays is making a strange sound rather than regular click. Maybe a have a bad relay that is responsible for switching in current?

Also I tried to measure resistance between input low and amp as I am going through different current ranges. It did change I think from about 2 Ohms to 90 Ohms, but was fluctuating. Tomorrow I am going to compare it to resistances I get from my other 2002. There is definitely a benefit from having multiples.

The firmware in the meter is A5. If you like a copy, I have a programmer and can load it in before upgrading the firmware.
TiN:
My older 2002 has A05, thanks. I'm still after miracleous B-version firmware for 2002 (saw once at ebay unit with B02).
Resistance from DCI jacks on my 2002 is:
200uA = 1.0194E3
2mA = 119.636
20mA = 14.5467
200mA = 1.2568
2A = 0.3491
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