Thanks for all the info!
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Unfortunately, none of those schematics match the layout in my instrument. For example, the PCB I have has no C20 (connected to pins 2 and 3 of U4), or any provision for C20 to be fitted.
A few resistors in my instrument are different values too, as are all the opamp part numbers.
I also have an R21, that doesn't seem to exist on the schematics as well.
I found the following resistors are different values:
R14 is 33R instead of 1K
R15 is 8.45K instead of 6.19K
R28 is 8.2K instead of 6.81K
R33 is 6.19K instead of 5.23K
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I also found the current pot was only a single turn (factory fitted) so I replaced it with a 10 turn pot. I think it was the same value but it was so long ago that I can't remember.
Also the output binding posts were red/red/black instead of red/black/green (for +ve/-ve/GND) so I changed the colours, but that would have no affect on the operation.
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I'm not sure what is up with this instrument, but I am pretty sure that I am the first one inside as far as I can tell, as I replaced the original leaking capacitors, and the solder joints look untouched (until I replaced caps etc).
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I'm having a problem where all the functions appear to work, except when pressing the Current Set button, where the display shows between multiple amps across the range of the current control, which is far too high for the instrument to be capable of.
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I'm thinking of just changing the resistors to match the schematic, to see if that will pull things into line.
Jared Cabot