Need help with iMac G3 700Mhz

[iChan]

I got this iMac G3 700Mhz for a song. The case is totally broken, but I did try plugging it in and it did start up, meaning the screen lit up and it tried booting. I only get a sad mac though cos there was no OS. So I took out the mother board and put it into a good iMac, but then it wouldn't boot. Nothing; and the screen doesn't turn on. I tried removing and re-seating, but still wouldn't boot/start.

I do get this light on the logic board:

And there was once where I got many "degaussing sounds" at like 1 second intervals like the monitor was trying to turn on. After that, I put the known good logic board back into the good iMac and everything is fine with it.

So, I really need some help diagnosing the problem.

I found this guide on ifixit:

SOLVED: its not powering on - iMac G3 Model M4984

braadan waid, okay so here is what Apple suggested for this model:" Testing for Power The iMac requires trickle voltage (+5 TRKL) in order to power on. If you are experiencing power problems in the iMac unit, you will want to test for trickle power to pinpoint the location of the problem and...

www.ifixit.com

So I tested J9 for trickle voltage, and it's giving +4.88 V, which seems to be OK, cos it's the same on my known-good board.
I've tested C4, and I'm getting -1.2V, which is what the guide says it should be.

Where the problem seem to start are with pins 2,4 and 14 of J7 connector to the Down Converter Board.

They are supposed to be:
Pin 2: +12V
Pin 4: +5V
Pin 14: +3.3V

but I'm getting
Pin 2: .63V
Pin 4: .15V
Pin 14: .1V

So clearly there is something wrong here.

Can anyone offer any insight or help?

I really want to get it working.

 

[barbu]

Good diagnosing! Not surprising it doesn’t work with those power rails not working. A good first step would be to inspect all the caps for deformity and leakage.