G4 Cube power supply blown?

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G4 Cube power supply blown?

Last week I had an electrician working in my garage. I completely forgot that he would need to kill circuits at the main panel. I left the house running with two desktop Macs running. When I came home my wife's G4 Cube was off and wouldn't restart (I could tell my G5 had been restarted).

I tried plugging it into a different outlet but still no results. A friend suggested the external power supply may have taken the hit and to test it with a multimeter. As I put the probes across the pins and the sheath where it plugs into the bottom of the Cube I only get any sort of voltage reading in one combination: the black lead on one of the four pins and the red lead against the outer sheath shows between 9 and 10 volts. Thanx in advance for any insights.

I have scoured the tech specs for the Cube and can't find any indication what the output voltage should be. Is this 9-10 volts normal or is the power supply blown? If it's not blown, I guess that would indicate a dead Cube, at which point it's time to take the back up drive and load it on to a new Mac Mini.

G4 Cube, Mac OS X (10.5.5)

Posted on Dec 24, 2008 10:57 AM

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Answer 1

Dec 27, 2008 4:40 PM in response to Ian Dodd

The Cube's power supply should put out 28 Volts DC. 2 of the pins carry the + lead, and 2 carry -. The shield is not connected to either side of the supply. It ought to put out 28V whenever it's plugged into the wall outlet. One silly thing to check - is the AC cord plugged all the way into the PS? Sometimes it stops just short of contact (don't ask how I know!).

There is a green LED in the left front near the DVD drive which lights whenever the power supply is connected. You can see a reflection of it in the "chimney", but it's easy to see if the core is out of the case.

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Answer 2

Dec 24, 2008 12:37 PM in response to Ian Dodd

Don't give up on your cube just yet. There is an LED inside, near the bottom, that indicates when it is getting proper power. By memory I am thinking it is green. If you examine the unit carefully, it can be seen through the outside enclosure at certain angles.

The power supply may not produce full power unless you start to load it appropriately. Some other Mac supplies, such as some PowerBook supplies, seem to produce almost nothing until you begin to draw power, so that you cannot measure their output except under load.

The most important question about your cube is, "How old is its internal backup battery?" Desktop Macs use an "always-on" (when AC power is available) power supply to maintain the Parameters. When the AC power fails, the backup battery is called into service to maintain the parameters. If it is too old and has deteriorated below about 3.2 Volts, it cannot maintain the parameters. Loss of date & Time, wrong screen resolution or "no picture", blinking question mark indicating can't find the right System Software, and inability to start at all can be the result.

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Answer 3

Ian Dodd Author

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Dec 25, 2008 7:02 AM in response to Grant Bennet-Alder

"The most important question about your cube is, "How old is its internal backup battery?" Desktop Macs use an "always-on" (when AC power is available) power supply to maintain the Parameters. When the AC power fails, the backup battery is called into service to maintain the parameters. If it is too old and has deteriorated below about 3.2 Volts, it cannot maintain the parameters. Loss of date & Time, wrong screen resolution or "no picture", blinking question mark indicating can't find the right System Software, and inability to start at all can be the result."

My guess is the internal backup battery is the original from date of manufacture. I bought this Cube used about 5 years ago and I know I haven't ever replaced that battery. I'll look for the green LED you described but maybe it's worth a trip down to my local Mac shop for a battery. Thanks.

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