Jerry wrote:
I traced the issue to a Chopper Stabilized Amp on the back of the power supply
board.
Unfortunately, the CSA has no schematic supplied. If it fails, it is to be
replaced.
I’ve been trying to reverse engineer it into LTSpice without luck.
There are two FETs, MFE3002 that cross to ECG220
Be careful of ECG and NTE parts -- sometimes they are so dissimilar to
the crossed part that one wonders how on earth someone thought they were
useful substitutes. I have data on the MFE3002, but not on the ECG220,
so I can't speak re: this particular pairing. I can tell you that
Mouser doesn't have anything even remotely similar (but I suspect that
some of the parts they do have can be made to work).
Alternatively, lots of great chopper-stabilized amplifiers are available
as ICs these days, so you might be able to replace the whole module with
one IC and a few other parts.
Do try to repair what you have -- if you post a schematic when you are
done tracing the circuit, we can help you get it working (if it isn't
obvious by then what is wrong).
I'm attaching the datasheet for the MFE3002 in case you don't have it.
Best regards,
Charles
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