Electronics > Repair

Yes, I bought another Keithley (196) to repair (FIXED!)

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staze:
So, just took delivery of a Keithley 196 I got for dirt cheap ($40). Which, for a 6.5 digit meter, can't be beat.

Initial diagnosis says it's probably something similar to what was wrong with my 199, which was the counts pathway between the analog and digital board (199 was the 74HCT04). Anyway, interesting that the 196 doesn't use optocouplers, but instead has pulse transformers (weird!).

First question is, does anyone have higher quality schematics for these units? the ones in the online pdf manuals are terrible quality.

Anyway, I'm working on physical repair of the unit at this point (shipping was un-kind to the unit), then I'll start (of course) with power rails, then I'm guessing TTL pathway, and I'm guessing the HC00's, or the LM311's that are in that same pathway. We shall see. Anyone else repaired one of these? =)

lowimpedance:
 The only repair I have done was for one at work which was needed for a test setup (old software etc) and was powered 24/7.
The failure was bad mechanical mounting of the mains transformer leading to eventual dry joint fracture and then burning of the PCB around that area. So my only input would be at least make sure yours is sound in that area.
 I did not need the handbook at the time and the owner probably would be unlikely to put his hand on it any time soon unfortunately.
If you still need better scans I 'might' be able to find it !.

staze:

--- Quote from: lowimpedance on November 06, 2013, 11:53:41 pm --- The only repair I have done was for one at work which was needed for a test setup (old software etc) and was powered 24/7.
The failure was bad mechanical mounting of the mains transformer leading to eventual dry joint fracture and then burning of the PCB around that area. So my only input would be at least make sure yours is sound in that area.
 I did not need the handbook at the time and the owner probably would be unlikely to put his hand on it any time soon unfortunately.
If you still need better scans I 'might' be able to find it !.

--- End quote ---

If you have the ability, that would be awesome. Judging by the scans, they seem to have been done with a really crappy scanner, or someone that just didn't care. So anything would be great... but don't go out of your way. I think I can get it fixed with what I have, but it sure would be nice to have better quality schematics. =)

rastro:
I also recently picked up a 196.  It seems to be functional and maybe 8-10 counts out on DC voltage measurements.  I still need to figure out accurate tests for ohms/amps/AC - certainly none are grossly out.  I sure like the large LED display.

I probably have the same documents you have from the internet.  My firmware is B15 and I think the main PCB is revision "C".  Let me know if you want me to cross check any test points or component values if that helps.

One thing I noticed is that the front panel seems slightly warm (90F with room temp around 78F).  I'm not sure if this is normal or there's a problem brewing.

Anyway good luck with your troubleshooting. 

tsmith35:
Would anything like this be helpful?

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