On 24/10/05, Mauricio Santana <[EMAIL PROTECTED]> wrote:
> I would be interested to hear an engineer's reasoning behind this.. [not
> that I am complaining... =)]
IANAE, but...
Capacitors ("caps") are one of the 1st bits of electronics to fail in
older computers. By electronics, I mean non-moving-parts; machinery
with motors dies first, generall. Fans, then disk drives.
Caps work like tiny batteries with a very short charge/discharge
cycle, "smoothing out" the flow of current by absorbing bursts and
releasing it in a slow & measured fashion, like a dam on a river.
This means they effectively charge & discharge millions of times.
Cheaper caps are generally of the "electrolytic" type. They work via a
chemical reaction occurring within them each time, like batteries. And
like batteries, they eventually fail.
When they fail, like old batteries, their contents react in an
uncontrolled fashion. Often the volume of reagents increases, bursting
the seams of the cap and allowing electrolyte to leak out. Thus, the
computer suffers problems from some of its components not working
correctly any more, causing partial failures - things like sound
becoming fainter and fainter. However, it's worse than that. This
electrolyte is by nature reactive, so now the computer has dribbles of
conductive liquid running across its circuit boards. If these reach an
IC (an Integrated Circuit - a "chip"), the liquid might run across the
chip's legs, making a short circuit ("short") between them. It might
make short circuits over longer distances between components, too, but
caps are small things, so there's not a /lot/ of liquid, meaning that
this is less likely.
Short circuits cause major problems and are quite likely to make a
computer stop working altogether.
What's worse, the electroytes are often corrosive and with actually
corrode any metal they contact, causing it to go white and fuzzy
instead of smooth and shiny. This reduces the efficiency of contacts
between components and the fuzz itself can be slightly conductive and
thus cause shorts.
So, failing caps leak, and thus cause 2 stages of problem: first,
intermittent or transient or partial failures, like dimming screens,
sound output getting quieter or perhaps occasional crashes.
Secondarily, leaking electrolyte causes short circuits within the
computer, causing problems like "simasimac" and then total failure.
But electronics are tough. They're made of metal and ceramic and
plastic. As long as they're not working at the time, they're
waterproof. If they /are/ working, water is conductive, so causes
massive shorts. If the shorts occur between power circuits and logic,
the large electrical currents flowing through delicate little circuits
can blow them altogether, causing permanent damage. Even bringing a
computer in from storage in a cold place into a warm room can cause
condensation to form within it, leading to this damage, which is why
you mustn't turn on a computer that's been subjected to this for a few
days - time to allow the condensation to dry.
So if you can remove the part affected by cap leakage, isolate it from
any parts that might sustain water or heat damage, like electric
motors or displays or fans or power supplies, then it's safe to wash
it, so long as you dry it /thoroughly/ before you try to use it again.
So, you remove your dead logic board and run it through the dishwasher.
Why a dishwasher? Well, it's non-mechanical cleaning. There are no
brushes or anything in contact with the board and it's not moving or
being shaken or agitated as it would in a clothes washing machine. So
delicate components, such as those on legs, shouldn't be damaged, as
they might by simply scrubbing it under a tap. All that happens is
that the board gets repeatedly sprayed with hot soapy water in a hot
wet environment for an hour or so, time to loosen and dissolve
dried-on deposits of electrolyte and other nastiness. If it gets off
all the electrolyte, and the cap isn't leaking any more or has dried
up, the computer might start working again. If the cap is now only
working marginally or wasn't completely essential in the first place,
dishwashing can effect a cure.
It won't remove corroded metal, though, so in severe cases, it won't
help. But if the machine's already dead, there's nothing to loose.
It's also a *lot* easier than trying to remove and replace the failed
cap, especially if you are not familiar with component-level
electronics work, particularly soldering. Added to this, more modern
computers from the 1990s often used robots to do the soldering,
allowing tricky techniques for humans such as surface-mount attachment
instead of the older pin-through-hole attachment. These are really
difficult for even a skilled solderer to replace, and when you
consider that the parts may be hard to obstain and the contacts on the
board corroded, it's an uphill battle.
--
Liam Proven · http://livejournal.com/userinfo.bml?user=lproven
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