Power supply (capacitor) works after months

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My 2007 AOpen PC would not turn on for months. I got a small flash when I
pushed on and then nothing. Today I was surprised with a miracle, it turned
on.  

THe computer I am using right now (1995 GW2K) behaved similarly a few years
ago and now works fine. (But it recovered more promptly).

WHich begs the question: do I need to replace both power supplies (one ATX,
the other microATX)?  If I turn the 2007 off in a few hours, will it turn on
again when I return?

In both cases the culprit seems to have been prolonged non-use.

My uncle, a frail 86yo EE, insisted he could fix it by just finding the bad
twenty five cent capacitor. And I've seen him fix bad capacitors by just
tapping them. (He sepnt the 1950s on WW2 submarines the USA give Greece.)


                    - = -
     Vasos Panagiotopoulos, Columbia'81+, Reagan, Mozart, Pindus
  blog: panix.com/~vjp2/ruminatn.htm - = - web:  panix.com/~vjp2/vasos.htm
   facebook.com/vasjpan2 - linkedin.com/in/vasjpan02 -  biostrategist.com
  ---{Nothing herein constitutes advice.  Everything fully disclaimed.}---





Re: Power supply (capacitor) works after months
On Thursday, December 5, 2019 at 5:11:08 AM UTC-5,  
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ad

Old timers used to (allegedly) *fix* bad electrolytics by tapping them with
 the back end of a wrench.  These were the metal chassis mount varieties, a
nd banging them would compress what was left of the electrolyte inside.  Sq
ueezing with pliers was another option.  Be aware that I heard of this as a
 lad back in the 1960s, so this would have been on older types caps, not wh
at we see today.

Compressing those old style metal can caps might have bought some time but  
I think squeezing modern paper electros would do no good at all.  When I ge
t to work, I'm going to try that on some bad caps and see if there's any im
provement in value and ESR.

Getting back to your problem, I think gramps is right; it's probably a tire
d electro (that would be "swell").  These almost invariably work far better
 when heated, so if the brick was sitting in a warm area, it might spring t
o life. Alternatively, you can heat the brick with a hair dryer or heat gun
 to get it to work, but these are only temporary solutions.  Crack the bric
ks open and change the electros with the bulged tops.  That will get most r
unning. If not, you'll have to either ESR or replace the rest of the caps.  
 Lower value caps on the primary side of the SMPS bricks generally go weak  
but don't swell or bulge.

Re: Power supply (capacitor) works after months
snipped-for-privacy@gmail.com says...
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are only temporary solutions.  Crack the bricks open and change the electros with the bulged tops.  That will get most running. If not, you'll have to either ESR or replace the rest of the caps.  Lower value caps on the primary side of the SMPS bricks generally go weak but don't swell or bulge.
Quoted text here. Click to load it

I agree, many of the capacitors made for switching supplies seem to go  
bad.  Often the tops will bulge out.  Sometimes heating them  will make  
the supply work but if you turn it off you have to heat them again.  

I have replaced capacitors in several pieces of gear and that seemed to  
be all that was wrong with them.  I had one piece of test equimpment I  
bought surplus.  It was made around 1995 and cost about $ 50,000 back  
then .  It was to test the older cell phones.  Bought it a few years ago  
and sometimes it would take about 2 to 5 minuits to come on.  It should  
start within a few seconds.  Replaced about 5 capacitors in the power  
supply and now it starts up in a few seconds like it is suppose to.



Re: Power supply (capacitor) works after months
There is physics behind with just letting it sit. CMOS logic chips can semi
-permanently change state with a surge.  Waiting, "along time", can fix it.
  I've used an accelerated method multiple times to fix stuff.  Bike comput
er (dragged over nylon rug), car clock (stopped after car was jumped), HPca
lculator (displaying commas for decimal points)

Re: Power supply (capacitor) works after months
Thanks to all.

I let it run 24hrs, then shut it off for a few min and turned it back on,
seems fine. The lesson for the last time seemed to avoid prolonged non use.

Aside:

A few years a had a supercapacitor watch. Spozably charged by moving.
I loved it. Then I got sick for over a week and the watch got uncharged and
never worked again. Bummer.  


                    - = -
     Vasos Panagiotopoulos, Columbia'81+, Reagan, Mozart, Pindus
  blog: panix.com/~vjp2/ruminatn.htm - = - web:  panix.com/~vjp2/vasos.htm
   facebook.com/vasjpan2 - linkedin.com/in/vasjpan02 -  biostrategist.com
  ---{Nothing herein constitutes advice.  Everything fully disclaimed.}---





Re: Power supply (capacitor) works after months
There is usually a cap in the startup circuit that can cause that. It will  
be on the hot side. Sometimes you got a resistor to the raw B+ which hits a
 source from a tertiary winding that powers the drive circuitry. Caps on th
e secondary side don't generally cause that, and even if they get slightly  
weak there are more caps on the mobo to take up the slack. If they get real
ly bad and the ones on the board are not enough you might get erratic opera
tion and maybe even data corruption. Even when it is not that bad those cap
s being bad can cause it to be more susceptible to momentary power glitches
 one of which just destroyed the OS in one of my boxes. I'm going to reload
 it one of these days but haven't gotten around to it. Lazy, and when I get
 unlazy I got work to do. In that one if the caps were in better shape they
 would have held a charge long enough, there were three outs of duration in
 milliseconds. It shouldn't have affected anything.

Re: Power supply (capacitor) works after months
On Friday, December 6, 2019 at 1:28:52 PM UTC-5, snipped-for-privacy@at.biostrategist.do
t.dot.com wrote:
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Be aware that that is exactly the symptom you get with an older, dying elec
trolytic.  Shutting off a few minutes will not be long enough for the warme
d up capacitor to cool it's core, particularly if it's a brick supply that  
isn't generally well ventilated.

I'm not saying a lazy cap is your problem, but it's a high probability from
 your description of symptoms.

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