I've got a G3 600MHz iMac with a slight burn mark on its logicboard which seems to effect part of the onboard graphics card. It cant do anything regarding 3D accel or even run a basic screensaver for more than 5 min, but otherwise it starts up quick and runs stable (iTunes, Camino, Wesnoth)
I'm just assuming its this odd mark on the board that's causing the issue, the machine actually passes every test on the hardware diagnostic CD... either way, I'm fairly sure there's a problem with the graphics card (fresh install of 10.3, new hdd, tested the ram)

My plan for it would be to jerk the CRT, its PAV, and the down converter board and replace it with an ATX power supply, using it a headless box... then build a fishtank out of its shell

The ATX conversion has been done often enough according to google, but only a few sites seem to properly document the actual wiring bit. I did find this image which seems to match my model


I've never messed with this before, but some of the practices that are apparently common seem odd
IE, because there's no pair for them on the ATX supply, AC+, AC-, and PT are left unconnected
And because only one pin on the ATX supply is +12 it gets split across 2 or 3
Also, because there isn't a 15V on the ATX, its either left off or shares the 12

I know you generally have to work with what you can get, but what are the consequences of those?
If the computer decides it wants AC+ and AC- for whatever reason, what does it do when it finds those aren't available?
If the processor and sound are both using the same 12V line, what happens? Could they overload it?
I'm not too worried about the firewire (the 15V) connection... I'm assuming I could leave it unpowered, just not use the port and the computer wouldnt mind

The iMac and the ATX have different ideas about how to turn on, the iMac send 5V and the ATX need a ground
Two different methods are out there, one using a transistor the other an inverter... both are fairly easy to implement, is there any reason one would work better than the other?

Ideas on any and all?

2/8/2008 10:24:18 PM

AC+/AC- are NEVER used on a modern motherboard, those are incoming line voltages, having them hit the mobo connector is a legacy crap design thing with imac units.

2/10/2008 8:29:53 PM