At 03:03 PM 8/6/99 -0400, you wrote:
>A beginner's question:
>
>One of our PC's decided not to power up this morning.  I checked outlet,
>power strip, fuse, voltage setting and power cord with no resolution.
>I'm guessing next thing to check is internal power supply.  I've never
>had to check/replace a power supply and I have a very healthy respect
>for things electrical.  What are the steps I need to follow up to and
>including replacing the power supply.  Thanks.

Power supplies will shut down in the event of a short cicuit condition.
Some rare ones shut down in the event of an absolute no-load condition as
well.

Is this an AT or ATX power supply?  For AT:

Look for a stray paper clip or staple laying inside the case (don't laugh,
it happens).  Then, if you find nothing unusual, unplug the MB, all drives
and auxiliary fans.  Turn on the power switch.  If the fan in the power
supply turns normally, the power supply may be fine.  If you have access to
a voltage meter, you can check voltages at the power connectors.  All
measurements are with the negative lead on the black wire:  Red is +5VDC,
Yellow is +12VDC.  Other colors may vary, but they are -5VDC, and -12VDC.
If all those check out, plug things back in, (turn power off before
plugging/unplugging) one at a time until the problem returns.  That can
tell you the bad component.

For ATX:

The stray paper clip etc. still applies here.  An ATX power supply has 5VDC
standby power for a simple momentary switch on the front of the case.
These switches are very light duty, and cheap.  They seem to fail
frequently (I've repaired two, and heard of many more).  I am not quite as
familiar with ATX as I am AT, so I do not know of the specific voltages or
characteristics of these power supplies.  If you want the voltages, some
other listers can get them for you soon, or I can get them in a few days.

If you don't know which type of supply you have, an AT has two connectors
going to the MB, a total of 12 wires.  An ATX has one connector, with a
total of 20 pins.

HTH


J. Paul Jones
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http://www.mindspring.com/~jpjcet/

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