Testing a Imac G5 Power supply... Need Help

[ClassicII]

Hey Guys, I have done some searching here and came up with some of the basics of testing my Imac G5 power supply. The unit board shows #1 LED on but the unit will not power on at all.

I found this pin out here.
http://www.xlr8yourmac.com/images/im...ply_pinout.gif

I have a 20" though I would guess the psu is the same but I am not sure. On that pinout one of the leads i think 12 is actually black on mine.

Anyway I would like to test the leads to see if this power supply is good.

I plugged it in and have 20v on one of the end corner plugs and 5v on the stand by. Thats it though nothing any where else.

I saw that i need to "power on" the psu by jumping it. how do i go about doing this on the G5 power supply? does it need to still be plugged into the board or can i do this with it unplugged?

Thanks in advance!!!!!

[Toasty]

Re: Testing a Imac G5 Power supply... Need Help

Welcome ClassicII.

I suggest using the search function on the forums. There are 19 topics on iMacs. Interesting reading and a ton of info on the PSU's and Midplane (Apple's name for the motherboard).

Search for: imac
Select from the drop-down box: Search Titles Only
At the bottom left- 'Show Results as:' click on Threads

See Post # 10 in this thread for LED indications-

https://www.badcaps.net/forum/showthread.php?t=7124

See Post # 37 for the connector pinout-

https://www.badcaps.net/forum/showpost.php?p=78821

Toast

Edit: What is the Model number of your PSU? i.e.- 661-xxxx

[ClassicII]

Re: Testing a Imac G5 Power supply... Need Help

Toasty, Thanks for your welcome and reply. I found that exact thread that you posted in and tried to test the ps that way. The thing is I cant get it to turn on.

I have 5v for the battery and 20v but when i try and jump the ps on it will not work or will only work for 1 second and then turn off.

I tried to do this on my G4 tower ps and when i try and jump it the computer fan will kick on for 1 second and then turn off.

Is this because its unplugged from the board?

[ClassicII]

Re: Testing a Imac G5 Power supply... Need Help

oh cant remember the model number but its a 20" rev A

[Toasty]

Re: Testing a Imac G5 Power supply... Need Help

>>Is this because its unplugged from the board?<<

No. These units will run standalone with the jumper only. The common problem with the pre-2006 units is cap failures. Don't jumper it with it plugged into the midplane.

>>oh cant remember the model number but its a 20" rev A<<

The model number is on screen side of the PSU case. Get it out of the computer case and have a look.

Check the caps on the midplane for bulging while you're there.

Toast