[sdiy] Do Electros Die Slowly?

[Harry Bissell Jr]

"Tantalum as intentional fuse" is a really good
idea...
as the basis for a novel or urban legend.  :^P

I'm sure that no Tantalum manufacturer specifies
(specified) the voltage their caps would "blow"
at... or how long they would take to "blow" or
how much current they would handle if they did... and
guarantee that they would remain shorted.

In most cases, the damage to other components would
probably be done by then.

Usually engineers do not rely on unspecified component
parameters.  Next weeks part can/will be different.

If the tantalum goes and is saves your @ss... you are
lucky, nothing more.

Much more likely is the difference in PRICE of a 16V
tantalum and the next size up, the 25V tantalum.
This is a massive difference, especially as the
capacitor size (uF) gets larger.  Check out a Mouser
or Digi-key catalog.

Now... they had a regulated supply, so they threw the
dice and said that 16V is good enough for a 15V
regulated supply.  I doubt they anticipated, or
planned
for failure.

People who planned for failure, even then... used a
zener diode, an SCR and a fuse to crowbar the supply
voltage if it gets too high.

Don't make the mistake (always) of choosing the same
voltage part if it was marginal in the application.
No reason not to sub the 25V part if it is available
and it fits in the board.

H^) harry

--- Bob Weigel <sounddoctorin at imt.net> wrote:

> Yeah it was kind of funny.  The customer said "Hey I
> tried even swapping 
> in this other board I had out of an omni 1 since
> they looked the same. 
> It heated up in exactly the same place! "
> 
> I promptly mailed him a cheap meter I had here which
> I precalibrated.  
> He reported 14.9V on the supply to the 100ohm
> resistor that isolates 
> that section.  That's about right.  They pair up 2
> 22uF tantalums in 
> paralell to get 44uF there.  At least one of them
> failed on both 
> boards.  I was thinking possibly we had an
> overvoltage situation but it 
> appears the power supply was fine. So he just
> soldered in the 47uF cap 
> that I sent him and hopefully all is well. Haven't
> heard back. --Bob
> 
> megaohm wrote:
> 
> > I never knew that, Bob. Thanks for the heads-up.
> This section has a 
> > fuse, but... if the 16V electros worked/work for
> 28 years (it was made 
> > in'78), maybe I'll stick with what is specified.
> >  
> > peng
> >
> >  
> > On 4/3/06, *Bob Weigel* <sounddoctorin at imt.net 
> > <mailto:sounddoctorin at imt.net>> wrote:
> >
> >     I just advised a guy today on an arp omni
> where they DO use that exact
> >     setup.  I think the tantalum caps are designed
> to be a kind of
> >     fuse....so that they soak down the power in
> that section so
> >     nothing else
> >     gets fried if the PS regulator fails.  -Bob
> >
> >     megaohm wrote:
> >
> >     >
> >     >
> >     > On 4/3/06, *Loscha* < loscha at gmail.com
> <mailto:loscha at gmail.com>
> >     <mailto:loscha at gmail.com
> <mailto:loscha at gmail.com>>> wrote:
> >     >
> >     >     running 16v caps at 15v is much too
> close for comfort
> >     >
> >     >
> >     > I agree. This is what is called for on the
> schematic and what was
> >     > actually used in the tape echo. If I replace
> them, it will be
> >     with 25V
> >     > or 35V. The pcb is tightly spaced but caps
> now are generally smaller
> >     > so it should be no problem fitting them.
> >     >   Still, I think this has little to do with
> the problem I'm
> >     facing (of
> >     > course I could be wrong about that).
> >     >
> >     > peng
> >     >
> >     >
> >     >
> >     >
> >     >
> >
> >
>