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Model A1225 / Mid 2007 and Early 2008 / 2.4, 2.8, or 3.06 GHz Core 2 Duo processor

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iMac won't turn on. Possible causes?

Hello,

I have an early '08 iMac that will not power on what so ever. I received this computer with this issue from a friend, minus the HD & RAM. I put in 2GB RAM and a spare HD (completely blank, new). I press the power button and 3/4 LEDs on the board light up. (One, two, and three, NOT four.) The CD drive makes a sound as if it is trying to detect a disc in the drive, but that is the only sign of life this machine is giving me. No startup sounds, no display response, etc. I've tried everything the Apple FAQ can provide and have examined the boards closely for burst capacitors, etc. Everything looks a-ok. Does anyone have a clue what might be causing it to not respond at all?

EDIT:

When the power button is pressed the fans do not come on either

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I'm thinking it has to be the power supply. Nothing else seems to make any sense to me. I'll get one ordered and if it was the problem I'll make sure to let everyone know here. Thank you for the insight!

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I'd check the power supply if the board looks ok, check out this old ifixit post sounds very close

Pinout voltages, No 12 volt on standby

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I've checked the PSU and it all appears to be fine. It also seems to be fine according to the post you forwarded me to. Any other way to test it?

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Dylan, how did you check the PSU?

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Per this guide:

iMac Intel 20" EMC 2210 Power Supply Output Voltage Test

If I'm understanding it right, Pin 5 should be 0V when powered on, and 3.8V in standby. I'm reading 0 either way.

I did notice when testing this that there's a very tiny wire disconnected on the opposite side of the board. It appears to have fallen out of a connector labeled "CN3". What does this wire do?

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I know this thread is old old, but it would be really nice to know what that strange tiny wire which goes to the "CN3" connector has for a function.

That wire seems to be present at all 24" Alu iMac (and other) PSU variant like 661-4478, 661-4665 or 661-4995.

Later PSU's, like these from the 27" iMac range hasn't this anymore.

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What is the work of cn3 wire

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I had the exact same symptoms with my 24" iMac EMC 2211 and replacing the power supply fixed the problem.

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Yeah same here it could be logic board or power supply

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If replacing the power supply didn't work try checking the CMOS battery.

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