[sdiy] Prophet 5 -15v rail is shorting... Need advice

[Gil W.]

It was a 25v tantalum.

However, instesting finds...

I now find that the +15v rail is not stable, i.e
voltage changes randomaly at the range of 14.50v to
14.80v instead steady +15v....

To make you be able to help me better here's the full
story:

I've been given a dead rev 3.2 , which was missing the
entire bottom/rear panel (and the power supply, jacks,
harness etc.)

I built a custom P.S basing on the schematics, and
used a Polysix transformer. I also recapped all
polarized caps, and all functions seem to work so far
!

Other than the frying tantalum problem I manage to
"hide" by using a regular cap, now I found that the 
+15v voltage rail is unstable, as I mentioned above.
Pitch is changing all the time accordingly.

This is more or less the situation.

Question -

Could it be that the transfomer used it not 100%
suitable for the P5 applications, therefore I both get
fried tantalums on the -15v rail, and lack of voltage
stability on the +15v rail ?

I'm incontact with someone who will probably be able
to sell me a stock, almost unused, original P5
transformer. Could this solve those problems or do you
believe there are problems in the circuit which make
things look like that ?




--- "Cornutt, David K" <david.k.cornutt at boeing.com>
wrote:

>  
>  From: Gil W. [mailto:gil_we at yahoo.com] 
> > I asked myself the same question - does any
> problem actually 
> > *exist* or is the tantalum just not good enough
> for this task 
> > ? I think the original cap was a 10uf/10v
> tantalum...
> 
> If it was really a 10V type, it was definitely
> under-spec'ed.
> This needs at least a 35V type, and a 50V would be
> better.
> 
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