[sdiy] Prophet 5 -15v rail is shorting... Need advice

[Gil W.]

Barry,

the first time I powered it all up I used small heat
sinks for the PS regulator (which I build, as I said).

Could the -15 regulator partially go defective, in a
way that it blows tantalums but works fine using
electrolytes ?

Thanks all !




======================================================



	I would wonder what would create high ripple on the
supply.
Tantalums should be fine.  Heck, we use em on disk
drives... tell me
 about
ripple...
Feel the electrolytic cap itself in use to see if it
is getting hot.
I just got one of those pc fan controllers that had
electrolytic caps
 all
over and they were blowing up and failing/getting hot.
 Poor design
 (extreme
ripple if you put it across the PWM output!), under
rated caps.
Could be there is a bad ground in the supply circuit
or a bad
 regulator.  It
may be oscillating etc.  A more tolerant cap may just
be covering up
 the
problem.

Barry




--- "Gil W." <gil_we at yahoo.com> wrote:

> Hi, thanks .
> 
> This particular v3.2 I got without its bottom/rear
> panel. I build the power supply myself, following
> the
> schematics, so you can imagine yourself that the
> powering system is not completely compatible to the
> designed one (I used a polysix transformer).
> 
> One thing for sure - with regular electrolytes used
> as
> main filter caps, I get perfect voltages. Could it
> be
> that the tantalum is too sensitive for heavy
> filtering
> applications ? I might consider taking it to a
> friend
> once I complete restoring it, and scope it. What
> should I ask him to look at ?
> 
> Thanks very much.
> 
> 
> --- GRAHAM ATKINS <gatkins at blueyonder.co.uk> wrote:
> 
> > Mmm,
> > 
> > I always think if the "designed" component is
> > failing it
> > suggests as you say an underlying problem before
> > this
> > stage. It does not pay to cover up problems which
> > could
> > lead to more serious damage to the keyboard later.
> > If it
> > was my Prophet 5 I would want to ensure it was
> > safe.....
> > PCB's not readily available !!!!!!.
> > 
> > I'd like to get a scope across the rails.
> > 
> > Graham
> > On Nov 7, 2007, at 16:23, Gil W. wrote:
> > 
> > > I asked myself the same question - does any
> > problem
> > > actually *exist* or is the tantalum just not
> good
> > > enough for this task ? I think the original cap
> > was a
> > > 10uf/10v tantalum...
> > >
> > >
> > >
> > > --- GRAHAM ATKINS <gatkins at blueyonder.co.uk>
> > wrote:
> > >
> > >> David,
> > >>
> > >> The electrolytic may be more tolerant than the
> > >> tantalum but
> > >> the underlying problem with high ripple off the
> > >> rectifier may still
> > >> be there, are you sure it is OK to connect to
> the
> > >> rest of the circuits.
> > >> Are you just covering up the problem ?
> > >>
> > >> Graham
> > >> On Nov 7, 2007, at 9:46, Gil W. wrote:
> > >>
> > >>> Hi,
> > >>>
> > >>> The problem has been solved by replacing the
> > tant.
> > >>> with regular 10uf/50v cap...
> > >>>
> > >>> Thanks all !
> > >>>
> > >>>
> > >>> --- "Cornutt, David K"
> > >> <david.k.cornutt at boeing.com>
> > >>> wrote:
> > >>>
> > >>>> Possibly either the rectifier has an open
> > diode,
> > >>>> or something else is causing the supply rail
> to
> > >>>> oscillate.
> > >>>> Tantalums don't like a lot of ripple current.
> > >>>>
> > >>>>
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