Re: I need help repairing a Yamaha SPX-90 (power supply is flaky)

[Richard D Pierce]

In article >,
Sam Lloyd > wrote:
>Anyone have any idea what might be wrong with mine? The PS is very
>"touchy" when adjusting the pot, and the voltages jump up above their
>proper levels (I get around 7-8 VDC on the 5V rail, and around 38VDC
>on the +/-18). I replaced the electrolytics and one of the
>optoisolators, but it's still screwy.

Sounds like it jas nothing to do with the electrolytics or
optoisolators. If it's jumping around when you adjust the pot,
it's a strong hint that the pot itself is flaky.

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| Dick Pierce |
| Professional Audio Development |
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[Gareth Magennis]

"Sam Lloyd" > wrote in message
...
> Anyone have any idea what might be wrong with mine? The PS is very
> "touchy" when adjusting the pot, and the voltages jump up above their
> proper levels (I get around 7-8 VDC on the 5V rail, and around 38VDC
> on the +/-18). I replaced the electrolytics and one of the
> optoisolators, but it's still screwy.
>
> Also, apparently this overvoltage has killed some of the digital ICs
> because the display doesn't display properly, and there's no audio,
> although the op-amps seem okay.
>
> Any advice?
>


Sorry, but supplying 8 volts to a 5 volt digital circuit is almost
guaranteed to blow some chips, and from the symptoms I think you're right.
I wouldn't waste any time or money trying to repair this unit and I don't
think many professional repair guys would either- pick up a used one
instead.

Gareth.