On Sat, Apr 24, 2004 at 09:14:19PM -0800, [EMAIL PROTECTED] enlightened us
thusly
> Hi Declan, Maybe this will give us some more clues: What kind of
> shorts and faults did you find? and where?
18V tranzorb(zener type object for supression purposes) zapped on both
of them in one 15V supply o/p. Power mosfet short circuit in one of
them.
They seem to work this way
Switcher A makes 2 indepent floating voltages
Switcher B, & C regulate each of the floating voltages to 15V
via another switched stage. I haven't traced the aux voltage,
but it is not in use and doesn't matter.
> Have you tried force
> feeding 24V to the second stage? (with a suitable current-limited DC
> source) How about replacing the +/-15V inputs with dummy loads?
Not yet. I thought enough of that had been done already. I may well.
As for the capacitors, I can verify them in circuit with analogue
signature analysis. They are not short, and both 15V supplies (blown and
unblown look similar to the signature analyser.
I can't trace the circuit, which disappears up it's own backside in
several places :-). The only thing I have to go on is that after power
up there is a small voltage on the untorched output which is not there
on the damaged one. That would indicate some safety check is being
failed. There are 2 hybrids which seem unnecessary to function but
obviously are.
I was hoping others had met the bizarre form of switching strategy used
here, but this appears not to be the case. Thank you all for your
thoughts on this.
>
> -Tony
>
> Declan wrote: I have the repair job on 3 dc/dc converters, worth a
> lot, but very awkward. They have a switched transformer feeding 3
> further switched stages (+24VDC in , +/- 15V out, &aux supply). Some
> problem fed 24V back up a +15V line. I have removed all visible shorts
> and faults, and still the input switched stage will not run, so the
> second 2 receive no power.
>
> I have 2 questions: 1. Why - what's it thinking? How does it know the
> outside supply is/was buggered?
>
> 2. Any ideas on this thing in the middle of this pcb. It looks
> like a pcb 'sandwich transformer', and has loads of connections
> off the pins underneath. The black part in the middle is ferrite
>
> http://homepage.ntlworld.ie/e-tronic.genius/smpsucard.jpg
--
With best Regards,
Declan Moriarty.
--
Author: Declan Moriarty
INET: [EMAIL PROTECTED]
Fat City Hosting, San Diego, California -- http://www.fatcity.com
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