[sdiy] Roland SH 2 power supply issues

[elmacaco]

Ok,

My SH 2 is starting to act funny, and after poking around, I need to appeal
to the gods here.

What happens is I get brown outs on the synth, occasionally, the power LED
will go out, and the synth will let a sound out, low pitched, loud, and it
isn't the oscillators, it is louder, but the osc's and filter still sound,
just softer and on top of the main loud annoying sound.  The filters affect
the osc's sounds but not the loud sound.

Since the power LED is out, I am guessing the +15V supply is what is
dropping out.

I changed the fuse and the Electrolytic capacitors in the power supply and
no dice. it still happens.

There are a bunch of polyester looking caps in the PSU, but I'd rather have
an idea that it would actually help.

This happens with the machine open so it isn't anything shorting from the
top part of the case.

It was hard getting a reading off of the power supply when this happens,
because it doesn't happen for too long, and whenever I set the ground probe
on the ground of the power supply, then the other probe on the V+ out of the
PS, it stops.

I did get one reading of +14V while it was happening.  At this point I'm
hoping it isn't the transformer, or the power regulators. (the regulators
get +20 V on the outside pins and the middle pin outputs +15, and -20V on
the outside pins of the neg regulator outputting -15 on the middle pin.

I really don't know where else to look now, so any ideas will be very
helpful and appreciated.

Thanks

Ed


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