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

[GRAHAM ATKINS]

Gil,

I would not worry too much about the slight variation in voltage
but you do not say if it is connected to the rest of the circuitry, if
not it will likely be even lower "on load". It sounds as though the
transformer is an unknown, any old transformer will not do. The
output voltage is a ratio of input to output voltage. It should have
a 110v primary side (In US) and a quoted secondary voltage. You
may be better off with the genuine item. Does the circuit diagram
not give you these details ?.

Graham
On Nov 8, 2007, at 9:18, Gil W. wrote:

> 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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