[Coco] OT -- PC needs TWO Shut Downs

[Gene Heskett]

On Tuesday 04 April 2006 00:11, KnudsenMJ at aol.com wrote:
>In a message dated 4/3/06 11:44:36 PM Eastern Daylight Time,
>
>gene.heskett at verizon.net writes:
>>>Generally it's the bigger caps by the PWM drivers for the CPU  core
>>>voltage that die first. All sorts of bizarre things begin to 
>>> happen.
>>
>>yes, and the majority of those are big enough to need  thruhole
>> mounting, so replacement is a piece of cake for someone  familiar
>> with hot solder.
>
>Great -- let's hear it for human-repairable.  The real question is, to
>diagnose whether these caps are bad, so as to justify the trouble and
> danger of taking the motherboard out of the case and subjecting it to
> the desoldering a soldering bench.

Well, the first and most obvious clue is that the tops of the cans, 
where they have the cross pattern embossed on them, aren't flat, but 
probably bulged upwards a few thou.  This comes from the heat generated 
by their riseing ESR (Equivalent Series Resistance) as they age.  The 
confirmation is of course when you measure the ESR at some suitable 
high frequency, like the 100 kilohertz that a gizmo called a 'capacitor 
wizard' ($175 when you can locate a dealer that has one) uses and find 
the ESR is well above 1 ohm.  Thats a definite no-no in those circuits.  
The go-nogo point in those should be not over 250 milliohms.

An enterpriseing individual could make this 'capacitor wizard' thingie 
and peddle it for a lot less than $175 too, its not really that complex 
a circuit.  Hey Roy, are you listening?  For those interested, see

<http://www.awiz.com/cwinfo.htm>

They may also have actually leaked a light tannish substance, usually 
out thru the bottom seals and onto the pcb.  This is slightly corrosive 
and should be removed by scraping the majority of it loose, and then 
rising it in warmish running water for a few minutes, with a final 
rinse of distilled & then cooked slowly with a hair dryer for long 
enough to get the water back out of the pcb.  That may take a while 
since it will migrate into the fiberglass of a good board worse than it 
will a cheap phenolic board.  Its the byproducts of the reduction of 
the ethylene glycol (yup antifreeze folks, but absolutely pure when it 
went in, no resemblance to that stuff in your cars radiator) and the 
kraft paper dielectric in the capacitor under high temps for an 
extended period of time.

Unlike the leakage of a nicad battery, which I have had destroy the pcb 
around it in relatively short times, this stuff is fairly benign.

Occasionally, one will actually get hot enough to pop that precut top & 
spew stuff all over, but in this application thats rare.
 
>FWIW, I assembled this whole PC from a "kit" consisting of the SB
>motherboard and custom case, plus other parts I ordered myself, all
> from Tiger,  Inc. When finished, I transplanted the HD from my old
> Win95 machine into  it, and it booted right up!
>
>Say, anyone remember the DOS command to make a HD bootable?
>Thanks, Mike K.

-- 
Cheers, Gene
People having trouble with vz bouncing email to me should add the word
'online' between the 'verizon', and the dot which bypasses vz's
stupid bounce rules.  I do use spamassassin too. :-)
Yahoo.com and AOL/TW attorneys please note, additions to the above
message by Gene Heskett are:
Copyright 2006 by Maurice Eugene Heskett, all rights reserved.