Powermac G4 MDD ATX Power supply conversion

[gibbo132]

My friend recently bought a Powermac G4 mdd 867MHz. It will not power on, the light on the power button goes on for a short time then goes off. I told him to replace the PRAM battery however that has not worked.
We have deducted that it must be a power supply issue. He will not pay £65 for a used replacement of ebay so we have looked into modding an ATX power supply to fit.
If I understand correctly we need a ATX power supply of around 400W, and then a 20pin to 24pin extension cable to prevent ourselves from cutting the power supply cables.
We then cut the pins to match the MDDs pinout. (Diagrams on another website)

Is this correct.
Any advice would be greatly appreciated! As the power light comes on for a short time it may not be a power supply issue so any advice on other possible issues (apart from the PRAM battery) would be fantastic!

Thanks
Chris

 

[adcx64]

My friend recently bought a Powermac G4 mdd 867MHz. It will not power on, the light on the power button goes on for a short time then goes off. I told him to replace the PRAM battery however that has not worked.
We have deducted that it must be a power supply issue. He will not pay £65 for a used replacement of ebay so we have looked into modding an ATX power supply to fit.
If I understand correctly we need a ATX power supply of around 400W, and then a 20pin to 24pin extension cable to prevent ourselves from cutting the power supply cables.
We then cut the pins to match the MDDs pinout. (Diagrams on another website)

Is this correct.
Any advice would be greatly appreciated! As the power light comes on for a short time it may not be a power supply issue so any advice on other possible issues (apart from the PRAM battery) would be fantastic!

Thanks
Chris

Press the little button on the Logic Board near the CD connector. This will reset your PMU. (power management unit) This may solve your issue.

 

[gibbo132]

No unfortunately he has already tried that

 

[gibbo132]

He made this short video showing the problem http://www.youtube.com/watch?v=q_T0_gNZlNk.

 

[ThunderSnake]

Is this correct.
Any advice would be greatly appreciated! As the power light comes on for a short time it may not be a power supply issue so any advice on other possible issues (apart from the PRAM battery) would be fantastic!

Yes, your understanding is correct. But another common failure in these machines is the power button board. There can be some overlapping in the diagnostic symptoms. If you wish to feel more confident before purchasing a PSU, I suggest following these instructions for a PSU test:

http://www.jcsenterprises.com/Japamacs_Page/Blog/D275729F-09DA-4FBB-96B3-BEEEB2C04619.html