[sdiy] sem repair

[epeasant at telusplanet.net]

An ESR or low range ohm meter would work for this. Just 
measure them all in-circuit, the one with the lowest 
resistance is bad.

But I doubt that the problem is a capacitor in this case, 
since the fault did not spontaneously occur on it's own but 
rather when somebody accidently shorted something. This 
type of fault is most likely to be a semiconductor of one 
type or another, so the op amps would be a good start, 
especially if they are in sockets. I've seen op amps fail 
shorted numerous times.

Take care,
Doug
______________________
The Electronic Peasant

www.electronicpeasant.com

> I'm curious here, let's say it is a cap (perhaps more
> than one), a rail
> to ground bypass cap, in parallel with a bunch of others.
>  I can't
> think of any good "trick" that one could use to determine
> which cap or
> caps is shunted or shorted.  The only way I can think to
> do this is to
> lift one lead (and leave it lifted) of each and every one
> and ohm them
> out or use a cap tester.  Is there a more clever way?
> 
> 
> cyborgzero at comcast.net wrote:
> >yes, definitely caps of some variety..
> >
> >I have seen things screw up a synth that defied logic..
> But, 9/10,
> >there is a cap out there dragging down a rail somewhere.
> ;)
> >
> >Rob
> >
> >----- Original Message -----
> >From: "Gene Stopp" <gene at ixiacom.com>
> >To: "synth DIY" <synth-diy at dropmix.xs4all.nl>
> >Sent: Friday, July 19, 2002 5:50 PM
> >Subject: RE: [sdiy] sem repair
> >
> >
> >> Tantalum caps?
> >>
> >> Best Regards,
> >>
> >> - Gene
> >>
> >>
> >> -----Original Message-----
> >> From: mark verbos [mailto:a0284520 at addcom.de]
> >> Sent: Friday, July 19, 2002 2:42 PM
> >> To: synth DIY
> >> Subject: [sdiy] sem repair
> >>
> >>
> >> Hi,
> >>
> >> I am fixing an Oberheim SEM and need some guidance.
> The owner tried
> >to
> >> trim the V/Oct response and sharted something that
> caused the power
> >> supply to blow up. I have replaced the 723 and got the
> power working
> >> again, with the VCO's cut off from the power. However,
> when they are
> >> connected, the positive rail drops from 15 volts down
> to 8 volts. I
> >> can't check what's wrong with the VCO's if the power
> isn't working?
> >What
> >> could cause this? I have never seen a dead OP amp mess
> with the
> >power
> >> rail. could it? Anyone know this problem?
> >>
> >> please help!
> >>
> >> mark
> >
> 
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