Re: Computer power supply capacitors - generic question

From: larrymoencurly (larrymoencurly_at_my-deja.com)
Date: 06/26/04 

Date: 26 Jun 2004 14:03:53 -0700

Sal Holland <salholland@ihatespam.com> wrote in message news:<lutmd0h7bt03el3mm8e3qb4h0k55hikuv1@4ax.com>...

> 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..

> 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, C11,C12, and C13 are all rated 16V
>
> Reading from the BIOS, the computer shows these voltages:
>
> CPU Core: 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

I've found that BIOS voltages aren't very trustworthy, and I've
personally seen one differ as much as 6% from my digital meter's
reading. Windows software readings are even worse.

Almost all the capacitor problems with mobos and PSUs were with the
low voltage capacitors because only they were the low-ESR types
involved in the counterfeit electrolyte problem that plagued some
Taiwan capacitor brands a few years ago, including Jackcon, JEE,
Luxon, and JGE but not Jamicon or Teapo. See www.badcaps.com and
www.motherboardrepair.com for more details.

I had a cheap PSU where the 16V capacitors for the +12V rail were
getting 50V peak spikes, but I saw nothing that high in a better PSU's
+12V.

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