[volt-nuts] Fluke 845A mystery

Frank Stellmach frank.stellmach at freenet.de
Sat Feb 4 16:28:18 UTC 2012


Following your description, any output deflection seems to load the 
+/-15V supply abnormally.

After having a look at the buffer caps C117/118, I would suspect the 
transistor pairs Q113/114, Q203/204, or Q111/112 for having a strong 
mismatch of current gain, or a simple malfunction.

(For the refs.: I own the old schematics from the 60's only)

Btw.: As your unit is of younger vintage, does it still have the optical 
choppers with neon bulbs, or has this been replaced by a MOSFET chopper, 
as in the 332/335 calibrators?

If the latter is the case: Do you have a schematic and would it be 
possible to get a copy, please?


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