[sdiy] Prophet 5 power supply issues solved - fuse resistor frying now

[klosmon]

First thing to do is isolate the problem area -- have you checked for 
a short on the +15 rail for each board ? (CPU, voice, front panel)
All three boards have bypass capacitors (originally tantalum) that 
can die, short out, and cause the problem you describe.

~G

At 01:55 PM 12/3/2007, you wrote:

>Hi all,
>
>You probably remember my DIY power supply issues,
>well, they seem to be solved as soon as I got the
>original P5 transformer (part number DP-241-8-36
>available from Digi-Key), and changed the electrolyte
>capacitors to tantalums, as on the original PS.
>
>Just to remind, this P5 I got with no bottom/rear
>panel and PS. The +15v filter cap on the main board
>was an electrolyte instead of the stock tantalum, and
>the fuse resistor was burnt out.
>
>I then decided to build the a PS, and had a few
>problems, among them, a frying -15v tantalum capacitor
>on the main board each time I powered it up, dropping
>+15v voltage, some missing and bad ICs on the voice
>board.
>
>Well, I put all missing ICs on the voice boards,
>replaced the bad ones, recapped all polarizes
>capacitors with new tantalums, and replaced to broken
>pots.
>
>After reaching this point, I no longer have any of the
>above mentioned symptoms, but new were coming up:
>
>1. I now get the +15v tantalum capacitor placed on the
>main board, frying each time I power up.
>
>2. When I replaced the cap with an electrolyte one the
>fuse resistor blown up.
>
>This brings me to the point where the previous owner
>decided to ditch the instruments. The tech who
>serviced it probably replaced the tant. with an
>electrolyte, like I did now, and got a fried fuse
>resistor.
>
>One note - the cap doesn't fry when I connect the main
>board to the PS, without being connected to the front
>panel circuit. The above mention problem occurred when
>I connect the main board and the front panel boards to
>the PS, keeping the voice board unconnected (to
>prevent from damage).
>
>This brings me to think that the problem lays in the
>front panel ??....
>
>Any advice ?
>
>
> 
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