[sdiy] Prophet 5 power supply issues solved - fuse resistorfrying now

[Mike]

> the power supply is new (I just built it) so I believe
> this is not the problem. I did use 6800uf gilter caps
> instead of the 6300uf the original used though. Could
> that cause the problem you mentioned ?

No: they should actually provide a bit more smoothing.

A definitive test however is to put  scope on the power rails, see if you
can borrow on -  a basic one will do for this: (try X at 5mS/division, Y at
10x probe,100mV/division and don't forget to set the input coupling to "AC",
then the trace won't go up/down out of sight), and see what the power line
looks like. If it's go big zig-zags after the regulators, you have a
problem. If the zig-zags are there off load, then the smoothing has a
problem. If they're only there on load, you have an excess current drw,
pulling the thing out of regulation.

HTH

Mike

> --- Mike <profpep at hotmail.com> wrote:
>
> > >
> > > So what seemed to solve the crazy voltage problems
> > and
> > > tantalum shorts, was simply using higher voltage
> > > tantalum caps !
> > >
> > > Although the ones I initially used are rated 25v,
> > > it seems they still could not hold the 15v rails
> > > efficiently, and simply got fried !
> > >
> > I haven't re-read the whole  thread, but have you
> > checked the ripple level
> > on these supplies. Excessive ripple will blow many
> > tantalums. The prime
> > cause of this could be the initial power supplt
> > electrolytics having dried
> > out. A ats check is to fit a known good new cap in
> > parallel. If the problem
> > goes away, change them out.
> >
> > I have a quite nifty capacitor ESR meter from Peak
> > Electronics. It will try
> > and read ESR in circuit, (power off!), and is useful
> > for checking suspect
> > caps from the parts bin.
> >
> > http://www.peakelec.co.uk/
> >
> > Their other little test instruments are good too.
> >
> > HTH
> >
> > Mike
> >
> >
> >
>
>
>
>
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