[sdiy] Roland SH 2 power supply issues

[Harry Bissell Jr]

I'd look for a broken solder joint myself. If it is
intermittant you could try GENTLY tapping all the
conponents with a non-conductive object (I like a BIC
pen).  Wiggle them a little bit and see what happens.

The Power LED could be going dim because of an open,
or
short circuit.  I'd suspect open circuit first, unless
you can see any evidence of a foreign object that
could have entered the enclosure (wire bit, solder
ball,
ObL whatever).

Putting the scope on it CURES it ??? That might be a
clue right there to the area the problem could be
in...

H^) harry



--- elmacaco <elmacaco at nyc.rr.com> wrote:
> 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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