Model A1312 / Mid 2010 / 3.2 GHz Core i3 or 2.8 & 3.6 GHz Core i5 or 2.93 GHz Core i7

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iMac doesn't start up, diagnostic led #2 off

Hello, This is my problem, i have a imac 27'' EMC 2390 and it doesn't start up. I found that when AC is inserted the diagnostic led #1 is on. If i push the power button nothing, the fan doesn't start, the hdd doesn't make any noise, no boot chime and led #2 is off. I tested the power button and it works. I also tested the logic board test point, and found 12V at the pin #4 (and in fact the led #1 is on), then, if i push the power button i found 12V also at the pin #11, but the led #2 is still off.

The imac was working fine, then a night i leave it on and i found in the morning switched off.

What can i do? Can i make other test to understand where is the problem, can be the power supply or the logic board? I don't want to replace the logic board, i would try first to repair it.

Thanks to all

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Hello, i've some news.

I made some test, first i reset the smc, and after that if i push the power button the fans start at maximum speed, but the diagnostic led #2 is always off.

I bought the schematic for the motherboard and found some test points for the various voltage.

I test the 3,3V at the test points near card reader connector and near bluetooth connector, and found exactly 3,3V

Then i test the 5V at the test points near camera connector, near ir connector and near sata connector and every time i found 0,10V!

So perhaps the problem is anywhere in the motherboard where the 12V of the power supply is transformed in 5V

Anyone with more skills can help me for find the broken component?

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The power supply appears to not be providing power to the logic board. I couldn't find any information on testing the power supply - maybe another volunteer has that information.

I agree replacing the power supply is a more "desirable" fix… but I would wait to see if someone has some DIY power supply testing tips.

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Giampy will be eternally grateful.
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