Electronics > Repair

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

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lowimpedance:
 Was about to post some thoughts on the said 680uF and bipolar stuff but you have already found the culprit, excellent. :-+
Another nice old meter saved. I have two 195a 's (5.5 DIGIT) which wont win any beauty contests but are good solid performers and best of all nice LED displays like the 196.
Hopefully the two 196's at work will become redundant before me ;).
 BTW that scope shot is what you get with filter caps that have 'dried out' losing capacitance.
With the 'new scanned' schematics you can zoom in and actually read the part details!. I printed one on A3 and its clean with no fuzziness as well as easy to read at this paper size.
 

staze:

--- Quote from: lowimpedance on November 15, 2013, 04:03:55 am --- Was about to post some thoughts on the said 680uF and bipolar stuff but you have already found the culprit, excellent. :-+
Another nice old meter saved. I have two 195a 's (5.5 DIGIT) which wont win any beauty contests but are good solid performers and best of all nice LED displays like the 196.
Hopefully the two 196's at work will become redundant before me ;).
 BTW that scope shot is what you get with filter caps that have 'dried out' losing capacitance.
With the 'new scanned' schematics you can zoom in and actually read the part details!. I printed one on A3 and its clean with no fuzziness as well as easy to read at this paper size.

--- End quote ---

Yes, pretty amazing. And good to know about that. I thought it was the VR, but I guess the filter cap makes more sense. So really the VR is only getting enough current when the BR is peaking. Will get those ordered, and also replace the ancient 1500uF cap on the 5V analog rail... the gigantic cap for the 5V digital rail appears much newer than 1986 (when that meter appears to have been built).

staze:
Ordered some Nichicon HE (10000HR 105C) caps to replace the two on the ±15V rails, and the +5V analog rail. Those should last well past my lifetime (since I don't plan on leaving the unit on at all times).

I don't plan to sell the unit, but I'm curious... anyone know what they actual go for? I see working ones on eBay for like $460, but I can't imagine they actually go that high.

staze:

--- Quote from: lowimpedance on November 15, 2013, 04:03:55 am --- Was about to post some thoughts on the said 680uF and bipolar stuff but you have already found the culprit, excellent. :-+

--- End quote ---

Though, please do post about the bipolar stuff. I know I'm curious. :)

staze:
Re-capped the power supply (replaced both 680uF 35V caps on the ±15V rails, and the 1500uF 25V cap on the 5V analog rail). Also put the original -15V regulator back (figured it worked, why replace it).

Now I'm just waiting for the Polypropylene cap. I really hope the calibration is still good... though I guess it wouldn't be to bad to have it calibrated considering how inexpensive it was.

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