Power Mac G4 (MDD) ATX Power Supply conversion
Submitted by eeun on January 6, 2009 - 8:53pm.
Apple | Hacks | Power Macintosh | Engineering Hack
I've just picked up a mirror-door G4 for cheap, sold as a "won't power on" unit.
After a quick test, and it does power up with a re-wired ATX power supply.
I picked up a better PSU, with a rating closer to that of the original, and wanted to know if there was any interest in having the process documented.
There isn't too much out there on mirror-door to ATX conversions, despite their flaky power supplies, so if there's some interest, I'll snap some photos while I'm doing the wiring and installing.
From what limited info I've found on the MDD conversion, the 28V is only necessary if you're going to use the ADC conector, and probably firewire. I'm not planning to do either.
Here's where I started:
(thumbnails are clickable for larger image)
One dead MDD power supply. When I opened it up, I found the fuse was blown. Tried replacing it, but the new fuse blew as soon as it was connected to the mains. There's nothing visibly wrong that might have been an easy fix, and the PSU is pretty densely packed and has a lot of silicon caulk applied to keep components from shifting. Better to start from scratch...
This is the ATX extension I'll be using for the connector. I'd considered cutting the ATX connector off the new PSU and soldering wire to loom from the MDD PSU, but thought this would be a bit cleaner and gives me the option of salvaging the new PSU if something goes wrong.
The wiring loom has been cut from the old power supply, and is ready for soldering. I used heat-shrink tubing to cover the solder joints. It's nicer looking than my old stand-by, black tape, and makes a stronger connection.
I picked up a 500W Cooler Master PSU that has a nice 120mm fan and an open grill at the back that should allow for good ventilation inside the case. The PSU will be mounted above the optical drives...which is as far as I can tell the only place a regular size ATX PSU will fit in that case.
The wiring in progress. After double-checking the wiring here and here, it's down to connecting the right colours together.
There are more 3.3V and 12V lines on the MDD PSU than are provided by the ATX PSU, so I've attached two MDD wires to one ATX wire in a couple of spots.
The only issue I had here was the 4-pin extension. I didn't have a female connector for that, so I relented and cut the ATX supply wires and used some spare wire to make an extension that would keep those 4 wires the same total length as those going through the ATX connectors.
If I need to salvage the ATX PSU at some point, it's only 4 wires to reconnect.
And the link where I got my inspiration from:
http://efeion.blogspot.com/2007/12/power-supply-fun-part-2.html
I've now got the power supply installed.
Based on the Twilight in Efeion blog linked above, and from my own test fitting, a regular ATX PSU will not fit in the case anywhere except above the optical drives.
I decided to use cable ties, as they're strong enough to do the job, and easier than making brackets and using rivets or tapping threads in the case metal.
With the case on its side and the motherboard up out of the way, I drilled four 7/32" holes, roughly eyeballed to where the case will be sitting underneath. I made a starter hole using a small bit first, as a larger bit will wander around the case metal before getting a bite.
The case was given a good vacuum and any metal flash still stuck to the drilled holes was knocked off. Don't want little bits of metal falling off onto the mobo once it's all back together!
It took six cable ties in total to wrap around from the top to join up under the PSU once it was in place. Cable ties do chain together nicely.
A view from the inside of the case.
Installed!
I threaded the power cord through where it would have connected to the old PSU. That's got to be addressed, as I want the G4 to look stock from the outside. I've got an idea for that...
One more check of the wiring, and then I transfered over my two hard drives from my Digital Audio G4.
OS X 10.4.10 boots fine, but waitaminit...OS 9 won't boot! What's going on???
Turns out the Mirror-Door G4 had its own special install of OS 9 and none other will work with it. Fortunately, I found I had the two-DVD install/restore discs kicking around.
I didn't want to mess up my OS 9 drive, so I installed the MDD OS 9 to a spare drive, then copied over just the system folder to my work drive. All better now.
Nearly done. Just have to work out that power supply connection to the outside of the case.
I've now finished the power supply, and the power cord plugs into the original location on the back of the G4.
Looking at the orignal power supply parts, I thought I'd be able to cut the casing up and connect a spare power cord to the old power connector.
note: to anyone considering this, the rest of this post deals with 120 VAC wiring, and care should be taken. Don't try this if you don't have experience with AC wiring. You can not only fry your computer, but yourself as well.
Here's the old casing cut up, and the cord that will lead from the ATX supply to the back of the case.
I used a jigsaw to cut the old case, then filed any flash and sharp edges with a file.
The cord is a right-angle one from a monitor, which should give me some extra room around the PCI slots.
Wire splices are done...in my case the two hots were black on the cable, and brown on the PSU; white and blue for neutrals and two greens for the ground. Verify your connections with a meter! Don't just trust the colours when working with 120 volts.
...and supported with cable ties. The pigtail connectors have also been wrapped in black tape for extra protection. The cable ties should prevent the pigtails from being moved or stressed.
There's only one hex-head nut that threads in from the back of the case to hold this on. Seems strong enough for me, but it wouldn't hurt to reinforce it.
Not much to see once it's installed. The wiring is hidden and protected by the old PSU's casing, and it looks stock from the back. Larger PCI cards will hit the power supply, but my SCSI card clears it and the power cord.
Back in business!
It looks completely stock from the outside, and I've managed to upgrade from my 867 MHz overclocked DA to Mirror-Door 1.25 GHz with a faster bus speed for a very reasonable price.
Original thread with discussion is located here