computer power supply

ATX by far the most common supply, often on sale _cheap_ and connectors are standard. The best 'test' is to simply put in another supply. They do fail occasionally especially if left on 24/7 and yours sounds like a dead one.

I think everybody should have a spare especially if they have more than 1 machine. Latest Fry's sale had a CoolerMaster 500 watt for $10 after the rebate so it won't break the bank to have one waiting.

Sounds like the 12 volts has died.

I would go for the new option too.

The most common problem I find is bad electrolytic capacitors. If it's a standard ATX power supply I usually just replace them unless I need it working in a rush.

In general they're not worth the bother of fixing as they're so cheap. Unless you have the required spare parts lying around.

I'm not using a PC for this task and when the power supply failed on this machine it was easier to adapt a PC one and fit it to this PS case than repair it.

Thanks to all. Yes the supply is dead. No 12 volts and the two sockets readings at 5.25 and 6.5 volt are not correct.

The above link was helpful. I do have a question though from the link. It says at the bottom of the page: "To power up an ATX or ATX-2 PSU for testing, short pin 14 (PS_ON) with one of the grounds" I did this and it made no difference. Does this mean on a good supply on the bench that these pins have to connect to get all the various voltage readings on the various pin outs?

Yes, and you should also have a load on the power supply, some less expensive supplies won't work correctly if not loaded.

If you plan on doing any computer h/w work, a p/s tester can be picked up for

Just like many other thingys,,, there is a big difference in Quality computer power supplys.You buy cheap, you get cheap. cuhulin

Personally, I prefer this one.

Unfortunately that test can only result in a probable result - a 'maybe'. Test that would have reported 'definitively good' or 'definitively bad' means disconnecting nothing, less labor, faster testing, and numbers that mean the better informed will reply. Less than two minutes using a 3.5 digit multimeter. A tool so 'complex' and 'scary' as to be sold to K-mart, Radio Shack, Lowes, Tru-Value Hardware, and Walmart customers.

Some good power supplies will not power when disconnected from computer with pin 14 grounded. Some defective power supplies will power when pin 14 is grounded. Some power supply problems may actually be created by the power supply controller which is also not found using a 'pin 14 grounded' test. Best way to identify a defect faster and to obtain numbers so that others will provide useful replies is summarized in "When your computer dies without warning....." starting 6 Feb 2007 in the newsgroup alt.windows-xp at:

Power supply testers are also inconclusive as the 'pin 14 grounded' test. Money for a power supply tester that will not provide a definitive answer, that has no other purpose, and that still cannot report a replacement supply as good? Same money is better spent on a multimeter. A computer can still boot even if the new supply is defective. Is a new supply good? Only useful answer means numbers from that multimeter when a best load - your computer - is connected to that new supply.

Grounding pin 14 can result in 'maybe the supply is defective'. Power supply tester can only imply a good supply. 'Maybe' means the supply and the rest of that 'power system' is still unknown. A 'system' has three possible states: definitively good, definitively bad, and unknown. Only way to establish 'definitively something' means numbers from a meter during maximum load.

my 3year old dell started having problems and it was the power supply . it would turn on fine and the lite on front came on,but it didnt compute right. lucas

I tested the power supplies at work and found some had the -5v line not working. Ive put these into systems and cant notice any difference between the ones with the -5v and the ones without. What is the -5v used for?

Most systems don't use it anymore. If it is used, it will be in an analog circuit, like the sound card. It was used for some of the early memory in the PC & XT, and has been carried over for 'Backward Compatibility'.

On Sun, 14 Sep 2008 17:07:02 -0400, "Charles" put finger to keyboard and composed:

That requires +/-12V. Some RS232 chips can generate both rails from the +5V supply via their internal charge pumps.

- Franc Zabkar

On Sun, 14 Sep 2008 01:08:57 +1000, Sleepy-Tom put finger to keyboard and composed:

The PCI bus does not use -5V:

I believe the -5V rail could have been used by ISA data acquisition cards. Some early DRAMs and EPROMs also required it.

- Franc Zabkar