Re: FG502 problem?


Tom Lee
 

The schematic shows that the -20V supply is derived from inverting the +20V output. So, if the latter is good, then the problem is with the inversion. Check U664 and associated components.

--Cheers,
Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 6/10/2021 17:25, Chris van Lint wrote:
Hi

I recently tried to fire up my FG502.  The unit was not working and the green power lamp was not illuminated. I discovered that one of the 741 opamps in the power supply was faulty.  I replaced the 741 and the unit now appears to be working OK.  However although the +20V supply is within specs, the -20V is way out at -30V. The +20V supply is easily adjusted with R625, but I cannot find any adjustment pot for the -20V supply. _The +17V and -17V supplies are also within specs._

- Does this mean that I should not be concerned about the -20V being too high?

- Am I correct in assuming that R672 on pin4 of U664 is out of range?

Any advice would be appreciated

Chris




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