PSU Problem or Not ?

  cosi 15:02 16 Jul 2007

My PC won't start; nothing runs - I hibernatede it some days ago, tried to start it today, no go. I suspect a PSU problem, but would appreciate another opinion.

Opening up the box: the mobo led is lit & when I connect pin 13 & 14 on the 20-pin connector, the PSU fan turns; however, I am not measuring the expected voltages at all the pins - I can find an occasional 5v, almost a 3.3v(2.5v actually), but no 12v; & all other PSU connectors read 0 on the red wires & 0.75v on the yellow.

It's the PSU, isn't it - please tell me it is :-(


  €dstowe 15:27 16 Jul 2007

PSUs do fail and they do fail in parts (some parts still show the voltages whilst the remainder is duff.

I've have several PSUs fail on me over the years. It's as though they wear out but I don't see how they can "wear" as there are no moving parts except the fan.

  cosi 13:35 20 Jul 2007

From other postings I have read, it sounds like my problem is the motherboard. Again I would appreciate a second opinion. Unfortunately I wasn't around when the PC broke, so I did not see or hear anything. Are there any other checks I can make or, if nothing works, it definately has to be the motherboard ? For example, what woud it do if the processor had failed ? does the little battery have any influence ?

Have just had a thought: do motherboards (in my case an ASUS P4T533) have fuses onboard, or anything like that - although the onboard power light is lit.

  umbongo(uk) 16:40 20 Jul 2007

proccesor are hard to fail

and usually you,d smell somthing acrid if it did
and it would make a pop when it did

onboard fuse,s no
they have built in thermal cut out this is to stop overclocking going its up
also they wont boot if they are grounded ie a screw or one of the motherboard risers is grounding it

1.make sure you dont have a usb stick in when booting

2 visual check
look on the mother board for burnt chips or leaking capacitors
capacitor are the cylindrical looking jobbie also check they havnt popped you can tell if they have because the top will be exposed

3.unplug all unnesersary devices only have the motherboard plugged in and the hard drive
try and boot
also only have 1 stick of ram in if you have 2
and do again with the second stick of ram if it dosent boot with the first one in this will eliminate bad ram

if it dosent post and no bios beeps are heard assume it is the psu

if it goe,s to the post screen
start adding each dvd drive and floppy drive
if it wont boot as you add components the psu on its way out

like edstowe points out it can be a voltage line tht goes yet it still give a false positive that power is being used

  sunny staines 16:45 20 Jul 2007

psu's often have a slight burnt smell to them when they go.

  woodchip 16:54 20 Jul 2007

When Testing volts did you Back Prob the ATX plug ? or remove it to Test! As it should be done by Back probing with tester while connected and switched on

  Fruit Bat /\0/\ 17:04 20 Jul 2007

I can find an occasional 5v, almost a 3.3v(2.5v actually), but no 12v; & all other PSU connectors read 0 on the red wires & 0.75v on the yellow.

Yes its the PSU.

  cosi 18:07 20 Jul 2007

I will run all the tests suggested & let you know.

In the meantime ...

I am fairly sure it's not the PSU, as I just replaced it, & unless I am very unlucky it's a pucker one, but still no joy.

No smells , but then I don't know when exactly it went ... but I know I wasn't around. I will have a closer look for leakage, discolouration etc.

To all, again thanks for the help.

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