Re: Slowly dropping Vdd values

The message <Y1ElZGDHiDfDFw+T@xxxxxxxxxxxxx>
from Mike Tomlinson <mike@xxxxxxxxxxxxxxxxxxxx> contains these words:

> In article <2005111705265885168@xxxxxxxxxxxxxxxx>, Johnny B Good
> <jcs.computersbutt@xxxxxxxxxxxxxxxx> writes

> > Not all the caps of same value and ratings fitted to a MoBo are going
> >to be equally pushed to their limits, so the 'survivors' may well have
> >years and years of service life left in them.

> My suggestion that all caps of a certain make and value wasn't
> predicated on the basis of their "survivability", but on the fact that
> most failed caps on motherboards are from those manufacturers that used
> the stolen, incomplete electrolyte formula.

> Those caps have a serious manufacturing defect, and the failure rate is
> 100%, so if you're going to strip a PC down and take the board out to
> replace a few, you might as well do the lot. Note I'm _not_ advocating
> re-capping the entire board - just the caps from the dodgy makers.
> Luxon and OST.IQ are two. www.badcaps.net has more info.

I understand your thinking on this but, unless you have detailed info
on the failure process involved, I would tend to leave the 'survivors'
in place on the basis that they weren't being stressed to the extremes
that the failed caps had suffered.

We're talking chemistry here, and it's a well understood principle that
increased temperatures will accelerate chemical reactions which also
includes the process of deterioration at issue in this case.

On a general principle, I would expect such capacitors to survive
longer by more than the square of the reduction of ripple current. The
surviving caps may well have only been subjected to a half of or less
than the ripple current involved with the failed caps.

Another point, it wasn't just a select few of the capacitor
manufacturers that suffered from this problem, almost every manufacturer
was effected and it's likely that you can count those that did escape
this fate on the fingers of one hand.

It's certainly prudent to replace any caps that look the slightest bit
less than pristine, but, personally speaking, I wouldn't bother
replacing caps just because they are of identical type and manufacture
as the 'blown' ones.



--
Regards, John.

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