[R-390] Shorting cap consequences

[Bob Camp]

Hi

The normal self healing event is a brief short to ground that quickly clears. It shorts (fails) and then un-shorts (heals). The sort of resistors and inductors running around in an R-390 are not going to burst into smoke from a very brief short. They die from heat and a short burst isn't going to heat them up much. You can indeed have a self healing event that does not even take the cap all the way to ground, they can clear that fast (very small mass, lots of energy). 

A dead short to ground that does not clear - yes that will do something. A dead short to ground is a full blown capacitor failure. That makes it an MTBF issue. I have yet to see any part that is rated for an infinite MTBF. They all fail some way some time, more so in a hot boat anchor than sitting at room temp. 

Bob

On Apr 28, 2013, at 8:14 PM, Perry Sandeen <sandeenpa at yahoo.com> wrote:

> 
> List
> 
> Wrote:>If it's a cap to ground, in general the answer is "not much".  Yes there are a few exceptions, but in general there is no massive belch of smoke from any vital part of the radio. Replace the cap and all is well.
> 
> I respectfully disagree with this generalization.  There are numerous bypass caps to ground after the use of a dropping resistor in the R-390A and SP 600 that will joyfully smoke upon a bypass capacitor short.
> 
> Regards,
> 
> Perrier
> 
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