Exactly how how do you test the PSUs out on the Apple iMacs?
How do you turn on the iMac G5 power supply when it is out of the computer?
iMac G5 Power Supply Connector – P-1
|1. +3.3 – BlackA3B
|12. +3.3 – BlackA3B
|2. +3.3 – BlackA3B
|13. +12v – BrownA3B
|3. GND – BlackB4B
|14. GND – BlackC4B
|4. +5v Gray/PurpleA4B
|15. On/Off – Gray
|5. GND – BlackB4B
|16. GND – BlackC4B
|6. +5v Gray/PurpleA4B
|17. GND – BlackC4B
|7. GND – BlackB4B
|18. GND – BlackC4B
|8. PG – Blue
|19. +12v – BrownA3B
|9. +5.1Vsb – Purple
|20. +5v Gray/PurpleA4B
|10. +12v – BrownA3B
|21. +5v Gray/PurpleA4B
|22. +20v to +24v – Brown
On the 661-3350 power supply and other similar PSUs, jumper pins 15 (gray) and 16 (blk/gnd) to turn the PSU on. With the power supply on, you should be able to read all the voltages listed above with a DC voltage meter. Between pins 22 and any GND pin, you will see approx. 24vdc, which is needed for the backlight. Note that the plug is numbered on the wired side of the connector plug. You will need some good lighting to see the numbers. A small flashlight comes in handy.
When reading the voltages, it is always a good idea to check both for proper DC voltage and AC ripple voltage. Note that AC ripple voltage should be relatively low, in the low millivolts range.
From what I have been able to tell, the other power supplies in both the 17 inch and 20 inch iMac G5 computers all used the same DC voltage pinout arrangements. I believe the voltage pinout arrangements are different on the Intel iMacs and some of the iSight models.
Please read the detailed information for repairing Apple iMac G5 power supplies.
Note: (see below) PG acronym represents the Power Good signal and VSB represents Voltage Stand By.
If anyone has more information for any of the power supplies (especially the pinout arrangement) used on the various Mac products, including the various PPC models, Intel Models, and Power Macs, please send it to me.
PG acronym represents the Power Good signal. I found the following reference in the Wikipedia when it comes to talking about power supplies in general for PCs.
In addition to the voltages and currents that a computer needs to operate, power supplies also provide a signal called the Power-Good signal, sometimes written as Power_OK or Power_Good or you can distinguish it by its gray color. Its purpose is to tell the computer all is well with the power supply and that the computer can continue to operate normally. If the Power-Good signal is not present at startup, the CPU is held in reset state. If a Power-Good signal goes down during operation the CPU will shutdown. The Power-Good signal prevents the computer from attempting to operate on improper voltages and damaging itself.
The ATX specification defines the Power-Good signal as a +5 volt (V) signal generated in the power supply when it has passed its internal self-tests and the outputs have stabilized. This normally takes between 0.1 and 0.5 seconds after the power supply is switched on. The signal is then sent to the motherboard, where it is received by the processor timer chip that controls the reset line to the processor.