[sdiy] Roland SH 2 power supply issues

[elmacaco]

Well, the meter probes cured it all times but once.

I tried resoldering all posts that had wires on it, but nor the components.
I'll give that a try Harry.

This thing doesn't look like any PSU I've seen, it has a 14 or 16 pin IC
where I would expect the bridge rectifier to be, and a SIP package further
down, in addition to the regulators.

I did replace the 10uF caps as well.

I am hoping it is something on the PSU board and not a wonky tant cap, or
them heated pairs :o

Ed
----- Original Message ----- 
From: "Harry Bissell Jr" <harrybissell at prodigy.net>
To: "elmacaco" <elmacaco at nyc.rr.com>; <synth-diy at dropmix.xs4all.nl>
Sent: Wednesday, March 17, 2004 11:34 AM
Subject: Re: [sdiy] Roland SH 2 power supply issues


> 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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