Quote:
Originally Posted by Beest
The purple wire was 3.38 V but dropped to 3.37 when the power button was pressed.
The green wire, the first time I measures it at 2.23V power on or off, when I measured it again after looking at the others it was 3.21 then dropped to 3.19 when the power button was pressed
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OK. First, a PSU is actually multiple power supplies. Purple wire connects a special voltage constantly and only to certain motherboard functions. That voltage is why all computer work must be performed with the AC power cord disconnected. Otherwise damage can result. That LED on the motherboard was also making the same warning. Only work on a computer when that LED eventually dims out.
Purple wire voltage (5VSB) is defective. Therefore a power controller cannot power on the system. However, the question is why? Is the motherboard shorted or is the PSU purple wire power supply defective?
Well, you measured the purple wire when disconnected from the motherboard at 5.02 volts. That only says it may or may not be defective.
Subsystems powered by the purple wire. Anything that might 'wake up' the computer including the keyboard, modem, and NIC. Also the Front I/O Panel is powered by the purple wire. It can be temporary disconnected where it connects to the motherboard.
In your BIOS setup would be a more complete list of those devices that can wakeup the machine. So, with AC power cord disconnected, remove any peripheral (ie USB device, modem card, keyboard, etc) that might be excessively loading the purple wire 5VSB. Reconnect the PSU to AC mains. See if that purple wire voltage rises up to about 5 volts. If yes, one of those removed devices might be defective.
We clearly see the defect. 5VSB (purple wire) well below 5 volts means the power controller cannot tell its power supply to power on. And cannot even let the CPU execute (power controller tells the CPU when it can work).
The green wire is the power controller telling the PSU to power on. But your numbers on the green wire confirm defective numbers from the purple wire. Therefore the green wire cannot go to near zero volts when the power button is pressed. Therefore the main PSU power supply is never told to power on.
Some will recommend jumpering the green wire to any black wire with a paper clip. In your case, the PSU will probably power on. So they will conclude the PSU is good. They would be confused. The meter says 5VSB - the other supply - has failed. Their 'paper clip' test would never see the defect. An example of why so many get confused when using observation rather than using a meter. An example of why the meter so quickly cuts through confusion.
Now, moving on to fixing it. The fault could be on the motherboard side or inside the PSU. If removing those other devices does not restore 5VSB. Then let's try any other test. After removing the AC power cord, then disconnect all PSU power connections to the system. Connect another PSU to that 24 pin connector (where you made measurements). Any PSU (even an undersized one) that has a similar 24 pin connector is sufficient. The second PSU need not even be in the system (if its wire is long enough to connect to the 24 pins on the motherboard).
Connect that second PSU to AC mains. Measure the purple wire voltage. It must be greater than 4.87 volts. If yes, then the first PSU has a defective 5VSB. If no, then the defect is somewhere else in your system (probably on the motherboard).
A second possible test. Again with the PSU disconnected from the motherboard. Buy some 100 ohm resistors from Radio Shack (maybe $1). Stuff maybe all four resistor leads into the purple wire connection hole. Connect the other end of those resistors to any black wire hole. Connect the PSU to AC mains. Measure the purple wire to black wire voltage. If not 5.02 (as before), then the 5VSB supply is defective - without doubt. If it is about 5volts, then the 5VSB supply 'might' be good. This 'load test' is a best option.
Or a third option. Buy a new supply. Connect it. Confirm the new PSU can provide sufficient purple wire 5 volts. Let me know if you choose this third option so that details can be provided.
Apparently the main supply inside the PSU is good. But a tiny 5VSB supply has either failed or has been shorted out by something on or attached to the motherboard. (Shorting out any supply does not harm that supply.) Above should help define which of two is defective. And says why the blue front panel light stays on constant.
Appreciate how much information was in those few numbers.