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.}---

On Thursday, December 5, 2019 at 5:11:08 AM UTC-5,

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.)


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, and banging them would compress what was left of the electrolyte inside. Squeezing 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 what 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 get to work, I'm going to try that on some bad caps and see if there's any improvement in value and ESR.

Getting back to your problem, I think gramps is right; it's probably a tired 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 to 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 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.

In article ,
says...

Getting back to your problem, I think gramps is right; it's probably a tired 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 to 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 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.



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.

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 computer (dragged over nylon rug), car clock (stopped after car was jumped), HPcalculator (displaying commas for decimal points)

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.}---

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 the 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 really bad and the ones on the board are not enough you might get erratic operation and maybe even data corruption. Even when it is not that bad those caps 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.

On Friday, December 6, 2019 at 1:28:52 PM UTC-5, wrote:
Thanks to all.

I let it run 24hrs, then shut it off for a few min and turned it back on,
seems fine.

Be aware that that is exactly the symptom you get with an older, dying electrolytic. Shutting off a few minutes will not be long enough for the warmed 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.