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

[Gil W.]

hmmm.... this is strange...

The panel board runs on +5v, no +15 / -15 there.

The +5v rail (which goes to the panel board) is
regulated from the +15v rail.

When I check the panel board out of the system, no
short is detected between +5v and ground.

Can an IC placed on the panel board short only when
being applied with current, causing a short on the
+15v rail ? As I said before, when I used electrolytes
instead of tantalums for filtering, the synth did
play, and all front panel functions did functioned
correctly,
but I had a voltage drop on the +15v.... Does it make
sense that I got only a half voltage drop on the +15v
rail *because* the short is on the +5v line and not
directly over the +15v line ? because has it was
directly over the +15v line, I'd get much lower
voltage read on that rail ??

As I said, when the only the main board connected, no
short at all - only when I add the front panel board
this happens.... But how do I determine the bad front
panel IC easily ??

Thanks for your help !!




--- klosmon <klosmon at sbcglobal.net> wrote:

> 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 ?
> >
> >
> > 
>
>____________________________________________________________________________________
> >Be a better pen pal.
> >Text or chat with friends inside Yahoo! Mail. See 
> >how.  http://overview.mail.yahoo.com/
> >_______________________________________________
> >Synth-diy mailing list
> >Synth-diy at dropmix.xs4all.nl
> >http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
> >
> >
> >--
> >No virus found in this incoming message.
> >Checked by AVG Free Edition.
> >Version: 7.5.503 / Virus Database: 269.16.13/1165 -
> Release Date: 
> >12/2/2007 8:34 PM
> >
> >
> >
> >
> >--
> >No virus found in this incoming message.
> >Checked by AVG Free Edition.
> >Version: 7.5.503 / Virus Database: 269.16.13/1165 -
> Release Date: 
> >12/2/2007 8:34 PM
> 
> 
> -- 
> No virus found in this outgoing message.
> Checked by AVG Free Edition. 
> Version: 7.5.503 / Virus Database: 269.16.13/1165 -
> Release Date: 12/2/2007 8:34 PM
> 
> 
> 



      ____________________________________________________________________________________
Be a better pen pal. 
Text or chat with friends inside Yahoo! Mail. See how.  http://overview.mail.yahoo.com/