PSU wont power PC up

kaaloo

Im confused and need help.

Im putting a PC together which is bog standard P4. The problem Im getting is that even though I know that all the components are working 100% (because I have checked them invidually in another PC), I cannot get my project PC to power up.

When I plug it in, my motherboard light comes on but the PSU fan will not power up. Occasionally, the heatsink fan may spin for literally 3 seconds but thats it.

Any ideas??

Mattjimf

Do you know for the power supply is the right one for the motherboard you are using? Some motherboards use more power than others and therefore need a bigger power supply.

T4i

If its not powering its own fan up then its fubar!

kaaloo

its a 300w PSU and the book says 250-300w is adequete. Is also has the P4 connectors so it looks right.

T4i

Yup, just sounds like its dead. Failed rail or something.

kaaloo

whats a failed rail?

fremar

kaaloo wrote:

whats a failed rail?

The term used above refers to a voltage rail.

The PSU will output various voltages ie +5v +12v -12v etc.

One or more of these voltages may be missing or low.

In short a new or replacement PSU required


fremar

Joe_Bloggs

Try and get the minimum you need to boot the PC. No hard drives CD/DVD rom remove their cables too. Pull out network,sound card, mouse, etc. Make sure that you have connected the heatsink fan to the correct heatsink fan socket. This socket is often monitored for fan speed and the system will not boot if it does not detect any fan revolutions.

Buy a higher rated PSU of a reputable brand rather than another 300W if the PSU is the problem.
J_B.

T4i

Joe_Bloggs wrote:

Try and get the minimum you need to boot the PC. No hard drives CD/DVD rom remove their cables too. Pull out network,sound card, mouse, etc. Make sure that you have connected the heatsink fan to the correct heatsink fan socket. This socket is often monitored for fan speed and the system will not boot if it does not detect any fan revolutions.

Buy a higher rated PSU of a reputable brand rather than another 300W if the PSU is the problem.
J_B.

Not too sure what this is gonna prove. If the CPU fan spins for a split second the PSU canot deliver the amps needed for it. If all the other components work on another the PSU is dead. Even if the PSU works without all the HDD's/CD's etc........the p.c will become pointless cas nowt will be attached to it.

Joe_Bloggs

I've done this to myself. The chasis fan header was next to the cpu header. I connected the chasis one to the cpu fan. You have to give a fan time to spin up before an rpm reading is valid. In my case the system would not POST.

Damaged drive cables connecting drives to the motherboard could be a factor as could a short underneath the motherboard.

The PSU is a component. Have you tried switching it. To a known good system ?
J_B.

drlight_2

I've had a problem with a not working PSU in a situation the same as kaaloo, it took me ages to find out what was wrong (psu was dead) in the end i hooked up a PSU to a working PC and that didn't boot. I'm sure I tested that before. Anyway it could of been a failed rail wich confused me and the fact that the processor psu was spinning up for a few seconds.

Anyway it was the main psu unit, send it back because it dosn't do what you wanted for or buy another one, although buying a brand name is a good idea if you want it to work, if you buy one that dosn't work don't accept it, send it back.
Al