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.


Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070

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

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


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