Powermac G4 : Help needed with PSU

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Joined: Nov 24 2011
Posts: 17

Tried the ATX modification, as I suspect a bad PSU, without much success. I have tried to modify 3 PCs power unit and each time, shorting Pins 11 and 12 on the MDD pinout would not fire the fan. And yet, shorting the green and black wires on the ATX pinout works, before the conversion !
Could it be the MDD adapter itself ? Thnks

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DrBunsen's picture
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Joined: Dec 20 2003
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Re: Powermac G4 : Help needed with PSU

First of all, you're much better off using an ATX power extension cable to do your wire mods. This way, you won't go through so many expensive power supplies as you experiment, and you can replace the PS at a later date, should it fail, with any off-the-shelf ATX PS, and plug it into your already modded cable.

You will find my experiences and links here:
http://68kmla.org/forums/viewtopic.php?p=12048#p12048

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eeun's picture
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Re: Powermac G4 : Help needed with PSU

What is the MDD adapter you mention? Is it home-built from an ATX extension? We need a bit more info about what you've done.
If you've tried three different power supplies, which worked before hand, I'd suspect the one adapter rather than the three PSUs.

Do you have a multi-meter, or even two wires connected to a battery and light that you can use to test the adapter cable?
Pinouts should match those listed here:
http://www.outofspec.com/frankenmac/wire.shtml

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Joined: Nov 24 2011
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Re: Powermac G4 : Help needed with PSU

The MDD adapter is the one, that came with the PSU and severed off, and wired out to the APX pinout to match the colours.
I have a multimeter.

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Joined: Nov 24 2011
Posts: 17
Re: Powermac G4 : Help needed with PSU

Food for thought, except mine is a Powermac G4/MDD

eeun's picture
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Re: Powermac G4 : Help needed with PSU

perryjoseph wrote:

The MDD adapter is the one, that came with the PSU and severed off, and wired out to the APX pinout to match the colours.
I have a multimeter.

I wouldn't trust the colours to be the same. They were on mine, but there's no guarantee.

What did you do with the white wire? On ATX it's -5V, and on the MDD it's +28.*
The white wires should not be connected together.
Also, the gray 'power good' wire on the ATX is unused in my conversion.

* The +28V line is only needed if you want to run an Apple ADC monitor. Possibly firewire devices too, through I've never confirmed that.

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Joined: Nov 24 2011
Posts: 17
Re: Powermac G4 : Help needed with PSU

There was no white wire from the ATX. Hence it was not connected.