Model A1311 / Late 2009 / 3.06 or 3.33 GHz Core 2 Duo processor

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No power, iMac is dead!

Hi,

I've got a 21.5" iMac that will not power on, there is no sign of life (no fans starting up etc). I've taken it apart and have noticed that only one of the diagnostic leds lights up but when the power button is pressed the led goes off.

So far I've re-seated the PSU, motherboard, tried disconnecting everything bar the power button from the motherboard, bypassing the power button, resetting the SMC and Pram but nothing seems to work.

I've been in touch with the guys at Apple and they have told me to try a new PSU first then if that doesn't work try a new motherboard. As you may well know this is a rather expensive suggestion, so what I ask is, has anyone else had the same problem and what was the outcome?

Thanks

Answered! View the answer I have this problem too

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Most techs use the swap out method as just being quicker when you get a dead system.

One could also use the meter/scope method. Where you use a Volt/Ohm/Current meter and/or oscilloscope, then using a good set of schematics and good electronics knowledge tracing out the paths and checking things out.

I would swap out of the power supply first - Sorry

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Thanks Dan, I've tried using a multimeter on the points on the motherboard and they all seem to be getting the right voltages.

I'm guessing that this means it can only be the motherboard at fault here. A strange thing happens when I hold the power button and plug in the power cable then release the power button and press it again, the fans briefly power on then off straight away, any suggestions?

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Remember you have more than one CPU in your system. The reaction you are seeing is the SMC being reset and then going though its reset startup process.

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Do you have a surge protector or UPS? As a voltage spike or dropouts can burnout a power supply and/or long term power fatigue can effect your logic board to the point of failure.

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We've had some bad storms recently and some power outages. The iMac was connected to a surge protector but I'm not sure how well these things work! Does the fact that the led on the motherboard is lit mean that it is more likely to be the motherboard and not the psu that is faulty?

Thanks

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Surge protecters do wear out and good ones cost more.

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JLB will be eternally grateful.
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