David, I would approach it from this perspective (and I suspect you have already done this as well).
1. Is the problem on this PCB? Do you have another board to swap with? If not, where else could the problem be? Obviously, all the connections and a 'soaked' PCB would be problematic. Time for another 'bake'? 2. If it is on that PCB, can you replace or clean the pot? Can you replace the Op Amp? Hope this helps but suspect you have already done these. Joe -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of David C. Partridge Sent: Friday, June 08, 2012 11:46 AM To: 'Discussion of precise voltage measurement' Subject: [volt-nuts] Help with 7081 AC buffer circuit Guys 'n gals, I'm looking for some assistance with this circuit. The OP16 op-amp has an offset trim pot which I can use to adjust the output DC offset with the input to the meter shorted - so far so good. The catch is that it's really *very* noisy, wandering by as much as 20-100 uV in less than half a second, and wandering around the zero set point by as much as +/- 800uV over a period of time (say an hour). This is much better than it was before I cooked the PCB for 6 hours at 120 celsius, as before I did that there was a huge monotonic drift as the PCB warmed up with the result that after an hour or so the DC output of the buffer circuit was many millivolts off. The schematic is sheet 70817506 Sheet 4. In the soft copy of the service manual which can be found here: <http://www.ko4bb.com/manuals/index.php?dir=09%29_Misc_Test_Equipment/Solart ron> it is on pages 117 and 118. I'm looking for any suggestions as to what component in this circuit is likely to causing this problem. Thanks David Partridge _______________________________________________ volt-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there. _______________________________________________ volt-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
