Possible faulty PSU ?

January 5, 2009 at 07:45:09
Specs: Windows XP, 2gb
A friends PC froze yesterday so I had a look at it........I rebooted but nothing happened. I HDD spun up but I didn't see the POST screen and the monitor displayed the message saying it wasn't getting a signal.

Long story short, I rebooted numerous times and occaisionally it'd boot to windows. I found that if I unplugged the two optical drives and left only the HDD plugged in, it would boot everytime. If I unplugged the HDD and plugged in only one optical drive, it would also boot consistently (although obviously it was unable to find any OS).

The only things that pulls power from the PSU other than the mobo are; two nvidia graphics card, two opitcal drives and one 160gb HDD. I have to confess that I don't know anything about the PSU. I don't know the make or the wattage etc. What I do know is that this PC has been working fine for a couple of years and no new devices have been added to it.

Is it possible that the PSU is faulty and unable to supply enough juice to run everything at once ?. I don't know much about PSUs specifically, I always assumed that if they were faulty nothing would work. Could it be that something has gone wrong inside the PSU and it is no longer able to supply the power it once did ?

thanks in advance for any help.

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January 5, 2009 at 09:19:15
How about supplying the specs? We have no idea what type/wattage PSU you're asking about, which video cards, etc.

HDDs & optical drives don't pull much power...each one takes < 1A from the +12v & < 1A from the +5v. So if you have 4 drives, they consume < 4A on each rail. Unless the PSU is teetering on the brink of being overloaded, they shouldn't cause a problem.

Are the drives PATA or SATA or a combination of both? If they're all PATA, they should be configured as follows:

primary master = HDD w/OS
primary slave = optical drive (reader?)
2ndary master = optical drive (writer?)
2ndary slave = 2nd HDD

or as an alternative:

primary master = HDD w/OS
primary slave = optical drive (reader?)
2ndary master = 2nd HDD
2ndary slave = optical drive (writer?)

It's best not to pair up two HDDs or two optical drives on the same cable/channel. Also, make sure all the master/slave jumpers are properly set...do NOT use cable select. And if any of the HDDs are Western Digital, they generally have a jumper setting for master (single) & master (w/slave). If they're set wrong, the system won't boot.

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January 5, 2009 at 10:13:51
"I always assumed that if they were faulty nothing would work"

Unfortunately, the complete opposite is actually true: If you have a crummy PSU it can supply dirty power to a seemingly stable system for months, maybe even years. The PC can boot and appear to run just fine, all the while draining the life of key components such as motherboard, graphics card(s), harddrives, CPU, RAM...pretty much all the hardware that needs power.

It is a common "n00b" mistake to cheap out on a power supply because there is no easily quantifiable justification for spending $250 when you can get the same wattage rating on a PSU that costs $25.

But when you start getting the BSoD more and more frequently, you'll know that the few bucks you saved just cost you the life of the rest of your computer.

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January 5, 2009 at 12:16:27
a psu supplies various different voltages on different coloured wires. it is possible that only a very minor part of the psu is faulty (as opposed to simply being fully alive or fully dead). i have known all sorts of intermittent faults cause by a faulty psu. only way to tell is to replace it.
Some PSUs have failing capacitors in them (bulging at the top of capacitors instead of being flat tops on them). that could cause intermittent faults eg. under load

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