[volt-nuts] DAS-46

[Charles Steinmetz]

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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