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?
Apple iMac G5 PSU With Ambient Light Sensor Shown
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 |
| 11. GND | 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 comment #13 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.
Thank you.
Regards,
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Jim Warholic says:
Hi Kim,
The powering down and powering up problem is typical of the the bad capacitor problem. I always say, you’ve got to fix what you find bad. In this case, having bulging caps on the MOB can in fact cause the problem you describe. I would definitely fix the MOB with new caps to begin with. Then, if you still have a problem, the original bad capacitors on the MOB could have caused something to go out in the PSU other than the PSU caps themselves.
Refer to my other Apple articles for more information.
Regards,
Jim
Kim Damsgaard says:
Hi Jim
Thanks for the fast response and help:-)
Regards,
Kim
Peter says:
Jim, I am testing the PSU from an iMac g5 20″ and only getting voltage from pin #9 at 5.2 v and #22 at 20.8 v while #15 and 16 are jumpered together. So that means my PSU is going to need some repair right, I saw, on visual inspection, only one cap with a slight bulge on top. Is my assumption correct as I am not getting any voltage or really about .27 volts out of the other pins that I will need to repair this PSU?
thanks for all your info on the website, so helpful really appreciate it.
Peter
Jim Warholic says:
Yes, you are correct with the fact the PSU is missing those other voltages. I would first start with the capacitors. It is also possible that something else may be blown on that particular power supply.
Guy says:
Jim,
I have a 20″ Ambient Light Power supply that does not work. I have not checked voltages, but visual inspection shows no bulging caps. I am trying to figure out if I should replace the power supply or try the caps first. I have seen many of these bulgig caps over the years so I know what to look for and none of these caps look bad. what do you suggest?
Thanks
Guy
Jim Warholic says:
Hi Guy,
I would say that you probably need to check those voltages first. Also, if the first LED does not light on the logic card with the PSU plugged in to the AC, but not turned on, then that is showing that something else is probably wrong with the PSU other than the capacitors.
Regards,
Jim
Guy says:
Jim,
I can’t figure it out but all of the voltages are like you said above. Could one of these things start working again after being discharged all the way? I am going to put it in the computer and see what happens. I have one of these and my parents also have one. Theirs stopped working so I took mine out and traded with them. Weird that it seems to be working.
Also on your pinouts #8 PG-Blue is 5 Volts. Another thing to note is that you can’t use the case for the ground on your meter. I used a paper clip to jumper 15 & 16 so I used an alligator clip to clip on to the paper clip for ground.
I was also told by a Dell tech to look for the X pattern on top of the capacitors, these were the bad ones. We had hundreds of GX270 motherboards go bad because of these bad capacitors. The replacement motherboards had capacitors with a K stamped into the top of the capacitors. This might help folks to figure out which ones an likely to be bad.
Thanks
Guy
Jim Warholic says:
Hi Guy,
It could be that when the PSU is placed under load, that is when the problem shows itself. It could be that something else is bad on the PSU.
Thanks for the input about the Dell motherboards. Dell was not the only one to have problems. I just heard a report that Samsung TVs had a similar issue with bad capacitors too.
Regards,
Jim
Kev says:
Hi,
Could you please explain what A3B, A4B, C4B etc do mean?
Thanks
Jim Warholic says:
Hi Kev,
That is what someone supplied to me for labeling. It may be where the wires go on the circuit board as a reference point. However, don’t worry about those specific references, just the wire numbers when measuring the voltages.
Jim
Steve says:
Hi,
Would you happen to know the pinout voltage for the backlight inverter? For a imac G5, 1.6ghz. (6 pinout)
Jim Warholic says:
Hi Steve,
Sorry, no information in that area. Maybe someone else that reads the comments knows the pinout voltages for the inverter or can point us in the right direction.
Regards,
Jim
Joe says:
How can I confirm that my iMac 17″ G5 PSU (P/N 614-0293) is working properly? I have removed it from the unit but I want to make sure it’s working before I proceed to repairing the logic board. When this PSU is out of the unit, do I also jump pins 15 and 16 in order to turn it on so that I can test the voltage values? Any help would be appreciated.
Jim Warholic says:
Note that the voltage pinouts should be the same between the 17 and 20 inch iMacs. Follow the procedure above for testing.