On Fri, 06 May 2016 12:05:35 -0700, wrote:

I have a computer that won't turn on unless it is warm enough. The
problem is in the power supply. If I use a blow drier to blow some
warm air through the exhaust holes in the power supply for a minute or
two the power supply starts working. I was told by someone here or on
the basics group that there is probably a bad electrolytic capacitor
causing the problem.
(...)

Those are the classic symptoms of a defective electrolytic capacitor.
You can't test an electrolytic with just a capacitance meter. you
need an ESR (equivalent series resistance) meter. Often, I see them
with the right capacitance, but with a high ESR. It's a common
problem:
http://802.11junk.com/jeffl/pics/repair/slides/bad-caps.html
Notice how some of them are bulging at the top or bottom. As others
have mentioned, it probably best to do an pre-emptive replacement than
to try an save a few pennies seperating the good from the bad caps. In
general, if one electrolytic is bad, they're all bad.

After some provocation by Phil Allison, I ran a temperature test on
various electrolytic capacitors:
http://802.11junk.com/jeffl/Electrolytic-cap-test/
Simple setup:
http://802.11junk.com/jeffl/Electrolytic-cap-test/test-setup.jpg
Test caps:
http://802.11junk.com/jeffl/Electrolytic-cap-test/caps.jpg
Spreadsheet showing results of temp test:
http://802.11junk.com/jeffl/Electrolytic-cap-test/cap-esr-test.xls
Notice how the ESR improves (goes down) with increasing temperature.
That's why your power supply screws up at room temperature, but works
when it's warmed up.

There are a number of different ESR meters available. If you plan on
doing such repairs in the future, you really should buy one. If
you're not sure which one is suitable, I don't have any experience
with this one, but it sure is cheap:
http://www.ebay.com/itm/131645169017


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558