[sdiy] Korg DW-8000 power supply

[Harry Bissell]

I'd agree. I find it really hard to believe that other caps were "re-forming" to make the voltage
slowly rise from 3.5V to 5V.  Re-forming usually does not take place politely unless you force it to do so.

Re-forming a dielectric in an electrolytic cap makes the layer thicker and able to withstand higher voltages.
Its likely that if you applied a higher voltage (5V) and the dielectric could not stand that voltage, it would
fail shorted. You would be relying on the regulator chip to limit the current in this case. I would not rule
out what you have reported, just that I'd look elsewhere (almost anywhere...) before settling on this as the
root cause.

I'd more suspect another capacitor that may have been shorted (like a tantalum) and that you heated it until
it opened up. Or some other explanation ???

Check your power supply current carefully on each rail if possible, and check to see if the regulator chips
are running hotter than you expect.

That sure is a curious observation. I'd look really hard, or put a lot of hours on the unit before I'd trust that
your repair is solid...

<twilight zone theme plays...>

H^) harry



----- Original Message -----
From: dragons <dragon.servicing at googlemail.com>
To: synth-diy at dropmix.xs4all.nl
Sent: Thu, 04 Nov 2010 12:46:09 -0400 (EDT)
Subject: Re: [sdiy] Korg DW-8000 power supply

Hi,
I wasn't sure if you just replaced one cap or all of them ?
I feel if one has failed then it would be worth replacing the others as 
they may have lost value and cause problems later on.
after all the cost of the parts is probably quite small !
regards Peter


On 04/11/10 08:25, Eric Frampton wrote:
> Resolved!
>

>
>
> Bingo. It was C11, the electrolytic that comes right after the block bridge rectifier.
>
> Interesting, I replaced that one cap and every rail came right back up. Re-connected the CPU board to the PSU, and

  one 5V supply immediately dropped to about 3.5V. Then, over the course 
of letting the machine sit for about a half hour,

  it kept rising until it finally settled at about 4.95V and remained 
there ever since. Might that be a result of bypass

  caps on that CPU board re-forming, or...? That was a new thing for me.
>
> Thanks for the help, y'all.
>
> Ericiy
>
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-- 
Harry Bissell & Nora Abdullah 4eva