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Model A1311 / Mid 2010 / 3.06 & 3.2 GHz Core i3 or 3.6 GHz Core i5 Processor

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No second light, is it referring to PSU failure?

No chime sound and no image on my 2010 21.5" iMac desktop, removed display, get it connected with power, the first light is on and stayed on, turn the machine on, fan started running, but the second light remains off all the time. In this case, should I conclude the PSU is failing and needs to be replaced? Any thoughts? Thanks.

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It's a good place to start. The second light usually indicates that the system is powered on. So first thing's first I would make sure you're trying to power up the system before checking the LEDs.

If this result persists after you have tried turning the machine on it could be absolutely be a faulty power supply. It could also be a faulty power button. But power supply is more likely and is a much easier fix since the power button is typically built into the whole chassis and is a bit a of a bear to replace.

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@Alisha - Thanks for the comment. I tried several times, and got the same thing, the machine can be turned on with fans running, those lights other than the first one all remained off. I also replaced the PSU with one removed from a dead 2011 imac 21.5 desktop (not sure if this PSU is in working condition), but same result, any more thoughts? Thanks.

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