how to check the serviceability of smps

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Sir,  my pc is not switched on, even the mother board lead don't glow.
so if i trace the problem,
how do i confirm  my smps is serviceable or not ?

Re: how to check the serviceability of smps

On Tue, 9 Dec 2008 20:39:46 -0800 (PST),

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How do you define servicable, what is this PSU worth, what
are the repair costs in your area, or what skills and parts
supplies do you have to repair it yourself?

You have not been specific, so I cannot be specific either.
Generally, hook the PSU up to an equivalent load and measure
the output voltage, and ripple if possible.

If that load can switch between high and low load conditions
rapidly, it becomes all the more similar to a real system.

Otherwise, the question is more fundamental.  Did this PSU
work to power the system originally?  If no, give up and
pick a different higher quality and/or capacity PSU.  If
yes, scrutinize what it's weaknesses are, where is it
llikely to fail relative to the load or line conditions
placed upon it.   One comon fault is capacitors, you might
examine them for signs of venting.  Another is transistors,
if system was subjected to a load too close to peak output
over time, or the line and/or filters were putting the input
voltage out of spec it could cause damage at the first
chance, if not later.

To test a PSU you have to subject it to (as close as
possible) the same environment as it saw in the system.
Otherwise, it may work for some kind of configuration of
load, but it is not proven to work for the load you need to
place upon it.

After removing it from AC then examinating it, the easiest
thing to do is measure  voltage and consider replacing it...
buying that replacement from a place with a good return
policy in case it wasn't the problem.

Re: how to check the serviceability of smps wrote:

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When the +5V standby voltage isn't present (what the motherboard LED
being dim typically indicates), it's an indication of the power
supply's main fuse being blown.  That fuse may be in a socket, but
more typically it's soldered in place.  If the replacement fuse also
blows, suspect a blown high voltage diode or transistor.

An old but still useful guide to computer power supply repair:

Re: how to check the serviceability of smps

On Fri, 12 Dec 2008 19:19:19 -0800 (PST), wrote:

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That's not necessarily true about the fuse.  I've repaired
quite a few PSU that had blown transistors but seldom is the
fuse blown.

The 5VSB circuit on the other hand, is indeed the subcircuit
that should be scrutinized if this motherboard LED is one
that indicates 5VSB power to the board (which it often is,
but not always).  

Generally speaking, a fuse should never be replaced until
the downstream part failure has already been replaced.  If
the fuse is replaced before this has happened, it can cause
more damage to the PSU or downstream, powered parts.  I
suppose I'm painting the wrong picture with this last part
since a PSU that has just been repaired or even merely had a
socketed fuse replaced should not be powering  computer
parts of any value until bench tested to at least meet spec
under ideal minimal load conditions.

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