With the iMac g3 you have to be very careful disassembling these as they are very brittle. especially the beige screen bezel. I gutted all the electronic boards down to just this metal plate at the bottom. 

Now I can start dry fitting all of the components, it looks like a M-ATX fits snuggly on that bottom bracket. Sadly, a full-size power supply does not fit on the underside. Originally, I had taken apart a 500w power supply had laying around and found the guts would fit on the bottom side no problem, no cutting necessary. It must have not liked being out of its original case since it quit working. So instead of gutting another PSU I bought a new 750w modular. had to cut a square hole in the bottom plate to make it fit though.

Cut the motherboard backing plate out of a junk computer case, built some brackets to hold it in place right above the bottom plate. This gives the PSU some room to breathe, I also added additional fans around the PSU area. The mother board will fit in almost any direction, but it fits best with IO towards the left side. This way the exhaust fan doesn’t hit the GPU.

 Looking for a 14-15” lcd at 4:8 ratio is little difficult. luckily, I found the ELO ET1523L off of ebay for $50. take the touch screen bezel off and the lcd part fit right with minor cutting. cut the original power cable end and spliced it into one of the PSU 12v cables. hot glued all the boards for the lcd to the back of the lcd. The only thing I don’t like about this monitor is that the ELO logo comes up when it’s started, other than that it’s a decent monitor with DVI inputs.

We wanted it to play the original mac startup sound when we hit the power button, so I bought the Adafruit audio FX sound board. With this board you can add .wav sounds that are triggered with ground input on one of the pins. The problem with ground input is there is no momentary ground output off the motherboard as far as I could find. So, I added a second micro switch next to the power button that triggers ground to that pin. The Adafruit FX sound board also has a built in 2w x 2w amp, so it doubles as a system speaker amp.

I wanted to exhaust as much air from this thing as I possibly could as I was worried about how hot it would get in there. I took a plastic bowl the same size as the handle area at the top and cut it to fit a 140mm fan. It moves a surprising amount of air and keeps it cool even when being tortured for hours.