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Power Supply on Mac G4

Message #1 - Posted 2004/04/15 - David Damerell

We've got a Mac G4 that someone (not me!) inadvertently plugged in to a 240V supply when set to 110V. The magic smoke came out of the PSU, of course, but nothing else visibly blew up.

I hooked it up to a normal 250W ATX PSU, and tried to turn it on; when I press the power button, the power light and some LEDs on the motherboard flicker, and the PSU fan jumps momentarily, but that's all.

I'm curious to know firstly if the machine should be expected to work with such a PSU, and secondly what might explain the observed behaviour. --
David Damerell <damerell@chiark.greenend.org.uk> Distortion Field!

Message #2 - Posted 2004/04/16 - Geoffrey

David Damerell wrote:

We've got a Mac G4 that someone (not me!) inadvertently plugged in to a 240V supply when set to 110V. The magic smoke came out of the PSU, of course, but nothing else visibly blew up.

I hooked it up to a normal 250W ATX PSU, and tried to turn it on; when I press the power button, the power light and some LEDs on the motherboard flicker, and the PSU fan jumps momentarily, but that's all.

That is not a good sign -- that usually mean the 'smarts' in the power supply are detecting a short somewhere and turning itself off. That, or the board and components are trying to pull more power than the PSU can provide.

Having seen what can happen when your typical PSU cops far too much juice, I would bet on some part of the motherboard (or an ancilliary component, such as a drive or card) has, as they say, had the richard blown out of it.

Did you try the ATX PSU with no cards and no drives attatched (i.e. just the motherboard)?

Geoffrey

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Message #3 - Posted 2004/04/16 - David Damerell

Geoffrey wrote:

David Damerell wrote:

We've got a Mac G4 that someone (not me!) inadvertently plugged in to a 240V supply when set to 110V. The magic smoke came out of the PSU, of course, but nothing else visibly blew up.

[and at power-on m/b LEDs flicker]

Having seen what can happen when your typical PSU cops far too much juice, I would bet on some part of the motherboard (or an ancilliary component, such as a drive or card) has, as they say, had the richard blown out of it.

Damn. I was afraid of that.

Did you try the ATX PSU with no cards and no drives attatched (i.e. just the motherboard)?

Didn't hook up the drives - no point - but I haven't tried yanking the graphics card yet, nor the stuff that sticks up from the m/b. I'll try that.

David Damerell <damerell@chiark.greenend.org.uk> Distortion Field!

Message #4 - Posted 2004/04/20 - David Damerell

David Damerell wrote:

We've got a Mac G4 that someone (not me!) inadvertently plugged in to a 240V supply when set to 110V. The magic smoke came out of the PSU, of course, but nothing else visibly blew up.
I hooked it up to a normal 250W ATX PSU, and tried to turn it on; when I press the power button, the power light and some LEDs on the motherboard flicker, and the PSU fan jumps momentarily, but that's all.

The answer turns out to be a little simpler, and I mention it for future reference; the Apple PSU does _not_ have the same pinout as a normal ATX PSU. One -12V line needs replaced with ground, and the "power good" line on an ATX PSU can be either +3.3V or +5V, but Apple specify a particular one of these.

[I suspect the latter doesn't matter, but I changed 'em both anyway.]

Fortunately the PSU had a single AT-style connector on it as well which I could cannibalise, so after a little work with wirecutters everything was fine.

Irritatingly, the case fan takes a funky connector, too, but I don't think this will be a serious obstacle. :-)

David Damerell <damerell@chiark.greenend.org.uk> flcl?

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