On Mon, 10 Jan 2005 06:58:02 -0800, OldGuy
<(E-Mail Removed)> wrote:
>Why? One of the most common causes that happens *without* users playing
>or fiddling is that the caps in the circuits dry out and eventually
>*pop*. Caps start dying from when they are made.
Yep. With normal electrolytics, it takes about 20-30 years for the
oxide layer to deteriorate. I've sorta watched people at the Computer
History Museum resurrect some of the old "computer grade" electrolytic
filter cazapitors from apparent death by going through the same
process as was used to create the insulating electrolytic dielectric
layer during initial manufacture. I don't know much about it, can't
seem to find anything with Google, and only know that it takes about a
week with a programmable power supply. Raising the dead is possible.
>YUP, you guessed it; electronics has a 'shelf life'! Normal operation
>should give years of use, but as you know; sh.t happens.
Sh.t not only happens, it's often manufactured. Many of the dead
electrolytics I find were simply defective. See:
http://www.burtonsys.com/bad_BP6/story3.html
http://www.burtonsys.com/bad_BP6/story1.html
>Thermal
>cycling of equipment speeds up the drying process. Just leaving it on
>speeds up the drying process. Not turning it on doesn't speed up the
>drying process, it just drys at it normal rate depending on relative
>humidity...
Sigh. There is no electrolyte loss or outgassing involved. I can
demonstrate if you want, but that's not the failure mechanism (trust
me). What happens is that the insulating oxide layer plated onto the
surface of the aluminium plates breaks down or disappears. The common
term "drying out" is a misnomer. Were it true, then one could
rejuvenate a dead cazapitor with an injection of whatever electrolyte
was used. There may be some outgassing for capacitors carrying lots
of ripple current and literally boiling the electrolyte, but normal
low power use will not cause the rubber seal to blow or vent.
>One of the major non-truths is "power cycling kills equipment". In
>terms of the electronics, all caps have 'surge' ratings, and if the
>equipment is/was designed correctly, turn-on ( even at just before peak
>) should not harm the equipment as the surge limiting resistors ( or
>active devices ) protect the stuff from the inrush current.
I beg to differ slightly. Cazapitors only conduct current during
power transitions. Powering on and off isn't much of a transition,
but applying raw AC ripple to a capacitor is. In such a circuit, the
capacitor is conducting perhaps 120 times every second resulting in
considerable power dissipation during each cycle. That's why
cazapitors get hot. The same thing applies to the CPU power filter
caps on the typical motherboard. They're trying to filter literally
hundreds of amps of ripple voltage at 1.8VDC. They get hot.
>Soooo, if you buy electronics and are planning on putting it on the
>shelve for a *long* time, don't.
Old electronics isn't exactly a great investment. Such things usually
end up in my storage area, or in the e-Waste pile. Want some klystron
microwave radios and test equipment?
--
Jeff Liebermann
(E-Mail Removed)
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558
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