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

[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.

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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 ?