[sdiy] Oberheim OB-Mx PSU question

[Sebastian Kuehnl]

--- Tony Allgood <oakley at techrepairs.freeserve.co.uk>
wrote:
> Hi Seb and all,
> 
> OK, that plate near the actual inlet socket aperture
> is removable
> without too much force. I actually can't remember
> how its actually
> removed, but it took me only seconds to work out how
> to do it with the
> unit in front of me. [Now if it were very hard to
> get off I would have
> remembered this all in detail :-) ]

I figured it out and it was easy as you say, but too
complex for my English to describe :^o


> There is a little switch underneath that simply
> selects between either
> 110 or 230V. The new voltage setting will appear in
> the window once the
> plate goes back. And its not paper but a white piece
> of printed plastic
> and part of the switch itself.

It's a piece of plastic that just needs to be removed
and inserted 180 degrees flipped. The OB is up and
running now. BUT...


> Also change the fuse inside to half the original US
> fitted value... I
> think you'll need a 250mA from memory.

The inscription on the lid says "use only with 250
volt fuse", and that's what's in there, so I thought I
shouldn't change anything. The local computer shop
told me they'd never seen anything like this, and
advised leaving the fuse where it is.

However, while the instrument runs, it hums like a
refrigerator. The 50 Hz sound comes from the PSU's
corner, is not audible in the signal path, and is
completely static (that is, no phase cancellations or
frequency changes were observed during several
minutes).

Conclusion?

Thanks again, any help appreciated.

Sebastian Kuehnl


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