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computer power supply

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by warrenl

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I turn on my computer and it makes a strange sound and turns off. I wait a short time and try it again, and it will try to start, but shuts down again.Is there some way to test the power supply by itself? Is there usually a circuit breaker or some other protection device in the power supply unit? This computer was "put together" and has worked great for 2 years.

7 replies

by thechas

You can buy a load resistor to use for 'basic' power supply testing.

I say basic because the average power supply load only loads the 5 volt supply.

One source is www.cyberguys.com

The average PC power supply does not have a circuit breaker. It does have current sensing, and will shut down if the current draw is too high.

Check and see if both the power supply and CPU fans start to spin up when you attempt to boot up.
If either fan does not spin up, you have a clue as to what failed.

It could be the supply itself, the motherboard, any of your plug-in cards, or even a drive.

I would start by removing your modem and or NIC card.
These are the most common cards to go.
If the problem persists, the next step is to swap in a new power supply.

Even 2 years ago, a 250Watt power supply may not have had enough power for your system, and may have failed from over-stress.

Next, take a good look at the motherboard itself.
What you are looking for, is signs of burnt or bulged parts, and signs of liquid leakage around the capacitors.
If you see any of these, the motherboard may be bad.

Chas

by warrenl

Found it was the fan . Housing all melted. Replaced fan and works fine. Thanks Chas

by csmith

This can have a lot of causes.
This problem can also be a short.
Check for loose screws, etc.
There is a power protection device in the PS.
If there wasn't a fire would occur.
Fires do occur occasionaly in power supplies for other reasons.
Do you have, or can you borrow, a voltmeter?
If no, start by unplugging components and testing.
I usually start with the hard drive.
When you get to just the motherboard and video card installed its probably the PS.
If you can borrow a voltmeter, check the +5 and +12 volts.
The +5 volt is the red wire on any empty plug.
The +12 volt is the yellow wire.
The ground is black.
The problem will be in the +5 or +12 for 99.98 percent of the bad supplies.
Regards, Chris

by rboggio1

Another thing to check is the CPU Cooling fan. Is it a three-wire fan that plugs into the motherboard or a four-wire fan that plugs into a power supply connector? If it is a three-wire connector on the motherboard, make sure the fan turns freely. (your observation of noise) Some motherboards have a monitoring system for such components and if the CPU fan does not reach a preset minimal RPM speed in a specific time it will shut down the system. This will also occur if no fan is attached to the three-wire header (connector on the MB). This is a failsafe component to prevent CPU overheating and burnout.

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