Re: Caps a poppin!

[Charlie Springer <RAM@regnirps.com>]

On Sat, 6 Jan 2007 02:38:23 -0800, Tristan Mumford wrote
(in article <459f7c41$0$38156$c30e37c6@lon-reader.news.telstra.net>):

> There were 2x 0.1uF burnt matchheads for a start.
> I also found evidence of a few other caps that have been replaced. The
> original caps (not the replacements) had also fried judging from remnant
> scorchmarks.
> However no other components show any signs of stress.
> I replaced the burnt caps (with unfortunately different values. better than
> lumps of carbon)

Wow!  A 0.1 mic is usually ceramic and rated at a lot more than 5 volts and 
without a failure mode due to age. I would suspect a power supply problem, 
especially with more than one failed cap. Would it wipe out caps but not the 
chips? It depends on how it happened. The anti-static protection in the chips 
might handle a spike that would cause a burn through in a cap, after which 
the cap would do a low resistance melt down at 5 volts.

Now, if they were tantalum electrolytic, I would suspect either backwards 
replacements or a voltage spike failure (and don't breath the vapor and wash 
hands after handling).

Either way, I would check the power supply. I get a lot of //e's with bad 
power supplies. Something in those Apple switchers does not age well. Often 
they will display symptoms much like you describe. Sometimes pulling all the 
boards out will lower the current enough for the supply to run correctly and 
boot OK. I have a box of new (new old stock, as they say) supplies from Sun 
Remarketing (and a box of new keyboards for Platinum //e) which 95% of the 
time is all that is needed to fix up a dead Apple.

-- Charlie Springer