i have fix a few pc supplys,
try replaceing the caps and resistors
that connect to the bases of the two
main switching transistors, you see some
values like 470k around them as well.
check all resistors around them transistors,
you may fine one or two near open or high.
and check for bad soldering joints.
these caps and resistors i call starting
resistors and caps. be cairfull thay are
dangeres!

john

"Sal Holland" wrote in message
...
I have a generic power supply that had the two main 470uF/200V caps
fail about a year ago (physically leaking, one had the top pretty well
opened.)

I replaced them with new caps from mouser (computer grade caps and
105c rated), and all was working well.

This year, the power supply is again exhibiting problems..upon a cold
boot, the computer will do about two reboots before it finally powers
up.

I was wondering if these voltage ratings on the caps, were too
low..seems like they should have higher rated caps then this I would
think.

On the -12V line, C1 is rated 16V
On the +12V line, C2 is rated 16V
On the +5 or -5V line, C3 is rated 16V
On the +5 line, C4,5 is rated 10V
On the +3.3V line, C6, C10 are rated 10V and 50V respectively
On the +5VSB (+5 Standby I am guessing?), C11,C12, and C13 are all
rated 16V

Reading from the BIOS, the computer shows these voltages:

CPU Co 1.69v
+3.3 is reading 2.94V
+5V reads 4.99V
+12V reads 11.49V
-12V reads 11.86
-5 reads -5.25
Battery Voltage (should be 3V) reads 2.88V
Standby Voltage (should be +5) reads 4.80V

As you can see, +12 Volts is pretty low, as is the +3.3 volt line. I
suspect these are what is causing the computer to reboot about two
times.

Are the 10 volt ratings of C4,C5,C6 all too low? Seems to me they
should have put some capacitors that had a little higher rating in
order to better handle transient surges, etc?

Are the 16V caps also too low for the +/- 12 volt lines? Would 25V
have been better or perhaps 50V caps? Or is 50V too high?