Re: Modifications to 577 Curve Tracer Main Power Supply

Ed Breya

OK, so with partial output to -7V, then it's likely the voltage on VR772 is stuck way too low (failed or dumped by C772), or Q772 is breaking down or leaking. If Q772 went open, it would go open loop overall, and the no-load output would be near the 40V raw supply. There are a number of ways it could have failed and makes -7V output, but I'd suspect the "772" parts at this point.

Yes of course Raymond, the output transistor would be turned on fully if it went open loop. I'm presuming it's still closed loop, with the failure limiting how high it can go. This appears to be the better kind of failure - not enough output rather than way too much, which could do some damage.


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