On 2019/06/25 6:54 a.m., Don Brown wrote:
I have a Hickok 440 curve tracer that I am having difficulty troubleshooting, even though it is a relatively simple circuit.

The base generator staircase is not stable, and will not stay in calibration. It looks like noise comes and goes and distorts it. I have replaced most of the semiconductors. The 15v power supply is a bit low at about 13.9v, though the regulator transistor and zeners have been replaced.

I have the manual, schematic, parts and usual test equipment.

Thank you,
Don


Have you replaced any and all electrolytic capacitors and verified that
the resistors are on spec?

Capacitors are bigger suspects than the semiconductors...

John :-#)#

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