It's dead Jim, PC help required, others may also opine.

[Beest]

No external devices have been connected, keyboard etc.

So I disconnected everything I could from the motherboard, optical drive, disk drive, video board, memory card etc.

Plugged in mains, green wire tested 2.23 and purple wire 2.34, no lights on the front power button.

Plugged all those peripherals back in, voltages still the same.

I don't have a 24 pin PSU too try, i do have a 20 pin, the green purple and grey wires are all in the same place, almost all of the other wires are the same. one of the red wires on the 24 is white on the 20.

I saw the paper clip test early in investigations, it does make the fans power on.


I found some 600 ohm and 1K Ohm resistors lying around and tried plugging them into the purple wire, also 2 in parallel, no voltage drop.

I look for some 100's

[tw]

Originally Posted by Beest

I found some 600 ohm and 1K Ohm resistors lying around and tried plugging them into the purple wire, also 2 in parallel, no voltage drop.

As you may have already seen, a defective supply can act good when not connected to a load. That is why the paper clip test says so little useful. That is why power supply testers are almost useless. That is why a power supply is best measured by not disconnecting a single wire.

The 5VSB should output maybe 2 amps (its label may say more). A full load is 5/2 ohms or 2.5 ohms. Radio Shack may still sell 10 ohm 10 watt ceramic resistors. One of those might be easier to use than four 100 ohms in parallel (25 ohms).

5 volts divided by 10 ohms is a half amp. If the 5VSB is defective, then a half amp load should cause some voltage reduction.

If those 10 ohm resistors are sold in pairs, then two ten ohm resistors means a full 1 amp load. A great test of the 5VSB. Those two 10 ohm resistors (that will get hot when held) should not cause the 5VSB to drop. If 5VSB does drop, the PSU's 5VSB (and not anything in the PC) is defective. That is a definitive and "you have found the problem" conclusion.

5 volts divided by 25 ohms (four 100 ohms in parallel) is 200 ma. Not a great load. But enough that can be purchased cheaply. The ten ohm ceramic would be better but I don't know if it remains available.

600 ohm or 1k ohm resistors are only 10 milliamps (only one LED) or 5 milliamps (less than 1 LED). Virtually a near zero load.

If the PSU 5VSB does not drop with that load, then the problem (excessive load) is probably located on the motherboard.

[Beest]

OK,got it.

Thanks for all your help with this.

[Beest]

Originally Posted by tw

Radio Shack may still sell 10 ohm 10 watt ceramic resistors. One of those might be easier to use than four 100 ohms in parallel (25 ohms).

5 volts divided by 10 ohms is a half amp. If the 5VSB is defective, then a half amp load should cause some voltage reduction.

If those 10 ohm resistors are sold in pairs, then two ten ohm resistors means a full 1 amp load. A great test of the 5VSB. Those two 10 ohm resistors (that will get hot when held) should not cause the 5VSB to drop. If 5VSB does drop, the PSU's 5VSB (and not anything in the PC) is defective. That is a definitive and "you have found the problem" conclusion.

.

Yes they do.
Purple to black
no load 5.02V
10 ohm resistor 1.26 V
2x 10 ohm in parallel 0.82 V

The green light on the back of the power supply dims out when the resistors are connected.

I tried the same test on another PSU I have borrowed (20 pin connector), minimal voltage drop with this test.

So is that definitive on the PSU ?

[tw]

Originally Posted by Beest

So is that definitive on the PSU ?

Yeph. That type of failure is typically a manufacturing defect. The defect may have existed many months ago. It was not a switch. A coin cell battery. Heat. A surge. Mishandling. The wife. Mystery currents from the plug. Failed motherboard. Defective BIOS. Bad CPU. Undersized video card. Intermittently getting loose wire. Dust. Undersized supply. Defective disk drive. Stuck fan. Or many suspects blamed on wild speculation to justify replacing parts. Another part of the supply that more often fails did not fail in yours. You had a failure of a tiny supply that should rarely fail. Sometimes, that entire 5VSB supply is only a single integrated circuit. A part that typically costs about $0.90.

Now, replace the supply. Ignore all discussion about watts as taught by advertising, hearsay, and A+ Certified computer techs. That supply should list an amp numbers for each voltage. A replacement supply must meet or exceed each DC amp number.

Of course, a new supply must have similar connectors, screw holes, and dimensions. Those dimensions are usually industry standard. Most important are ampere numbers for each DC voltage. Simply meet or exceed the number for each DC voltage.

A supply costing less than $60 is typically missing essential functions. That does not say a greater than $60 supply is better. That only says anyone selling a supply for $40 should be selling it for near zero profit. Or the supply must be missing essential functions.

When installed, one simple test will confirm the new supply is not defective. A defective supply can still boot a computer. But about one minute of labor quickly identifies some defects before its warranty expires.

[Beest]

any suggestions on where to look, or good brands?

$49 for a refurb, no detailed voltage info.
http://www.discountelectronics.com/i...detail&p=13852

or
http://www.amazon.com/Original-Genui...N%3DB005W39F7O