The iMac G5, powered by the PowerPC G5 processor, was originally released in 2004.

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iMac Power Issues - Light On, Fan On, Fails

I have an iMac from 2005, model #A107, a refurb with the serial #RM5461SESDZ. For the last few weeks it was having some strange sleep patterns--as in, it wouldn't go to sleep when you tried to put it to sleep. Before I could investigate further, today it simply died and won't turn back on.

Rather: when I turn it on, it sounds like it is trying to boot--the light comes on, the fan spins, and then it sounds like it is getting hot and the fan spins wildly and then it dies. The screen does not come at all--no question mark, no nothing.

I removed the back and dusted it all with compressed air. I did all of the restart attempts, removing plug, etc. I pushed the power supply reset button. On the motherboard I tried resetting the SMU--same thing. There are four lights (?) and when I power up the two to the left light up.

So, question: does this appear to be a power supply issue? I'm happy to purchase and repair myself, but I have no idea if this diagnostic is leading me in this direction.

And I did look at the capacitors and noticed no bulging or leaking.

Any help or advice would be GREATLY appreciated. Thank you!

Answered! View the answer I have this problem too

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Chosen Solution

Plug it into an external monitor and see if you get anything then we can proceed.

LED 1 inicates that trickle voltage from the power supply has been detected. This LED will be ON when the computer is turned off and your power supply is working correctly.

LED 2 indicates that the main logic board has detected proper power from the power supply when the computer is turned on. This LED will be ON when the computer is turned on and the power supply is working correctly.

LED 3 indicates that the computer and the LCD display are communicating. This LED will be ON when the computer is turned on and video signal is being generated.

LED 4 lights only if the computer detects an over-temperature condition. This LED will be OFF when the computer is turned on and running at the correct temperature.

So plug it into an external monitor and see if you get anything then we can proceed.

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Thanks for the quick response.

With the back off, I plugged in an external monitor, inserted the power chord, and turned it on--but the same thing. My monitor said 'Test Good' whatever that means, but nothing on the monitor. The computer never boots--no sound, just the light comes on and the fan starts to spin. After about 30 seconds the fan starts to spin much faster and that's it. Nothing on the screen, no nada.

I tried to boot in target mode or to boot from DVD drive but to no avail--it just doesn't seem to get far enough.

The LED lights: with the plug in, LED 1 is on, with the power turned on, LED 2 is on. 3 and 4 never light up.

Thanks again,



Here is a link for some additional info. Ralph


Ahhh, thanks. No LED 3. Looks like it's the logic board. Guess I'll be getting a new computer!


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Michael Falter will be eternally grateful.
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