Ok, first off - you can make an iMac g5 come alive again with just a standard ATX (PC) power supply. It's a bit ugly, and the screen doesn't get the 20V it's supposed to, but... it works.
I don't suggest doing this if you:
A. have the money for a power supply from apple ;
B. don't have a broken iMac that's acting as a paperweight
C. have really (no) experience with wiring anything
D. are afraid of electrocuting yourself
Are you having problems with your Apple iMac G5 17 and 20 inch iMac?? Does your iMac turn off by itself? Are you seeing strange graphics on the video screen? Is it to the point where it doesn’t even turn on anymore? Is it running hot and the fans sound like a vacuum cleaner?
OK ! Right on.
I bought a broken 20" iMac g5 on Ebay for $100. One can be purchased for next to nothing when they crap out and decide to stop functioning. I looked hard for one that was (obviously) a power supply related problem. Now, replacement power supplies don't come cheap - so I planned on fixing mine using the capacitor replacement technique, and it didn't work. I replaced about 5 Capactiors, then I gave up and decided to wire up an ATX psu from an old junker case I had lying around in the garage.
For more info on the capacitor replacement goto:
Capacitor List and Diameter Sizes For Power Supply :: Apple iMac 20 Inch
330uf 35v 10mm
1200uf 16v 10mm
3300uf 10v 10mm
2200uf 10v 10mm
1000uf 25v 10mm
1000uf 10v 8mm
120uf 50v 8mm
Basically, find the 'pregnant' looking ones (or burned up ones) and replace them. It's not as easy as it sounds, because you'll need a really hot iron to heat up the solder points on that PSU board, and you have a lot of tiny SMC (surface mount components) to look out for when you do the job. Here are some photos of my capacitor nightmare ; and an example of a bad capacitor.
Step 1: Find an Old ATX Power Supply
Take apart the iMac, disconnect the power supply.
Take the power cable from the iMac and hack it off so you have some lengthy wire leads and the iMac psu plug which goes to the Motherboard inside the iMac.
Take the ATX power supply and snip off the mainboard power plug. Leave enough cable for soldering together the two ends.'
Use the photo guide below to wire up your PSU to the iMac power supply harness.
** optional :: USE AN ATX-ATX extension cable so you don't ruin your PSU's wires :: **
Solder the iMac power plug to the ATX power supply making sure to match the power supply values of the iMac g5's plug , then give the monitor line (20v) 12v . Use shrinking tube for insulation.
The next goal is to get a DC-DC upconverter that as I understand it will take say a 12V 3 Amp line and up voltage to 24V 1.5 Amps or so.
Step 2: Living With a Big ATX Psu
So yeah, it doesn't fit (inside) your pretty-in-flat iMac... but now it's no longer a paperweight!
Remember the 20V line of the iMac's power plug will get 12V ... and the LCD will fire up. On a 20" it occasionally flickers but it works.
Connect the yellow cables (12V) to pin 12 & 18 and off you go.