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

[Travis Shire]

> 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 ?
>

Since you *built* the supply from scratch, I'd  check your layout/lead dress
and make sure the grounding is solid. The polysix is  similar  to the
prophet for power requirements (just +/-15 and 5v for the logic right?) so
there's no need to chase down a "real" prophet xfmr.
Perhaps you'd be further ahead to get a regulator board from something like
a poly61 or similar semi worthless board.