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Model A1312 / Mid 2011 / 2.7 & 3.1 GHz Core i5 or 3.4 GHz Core i7 Processor, ID iMac12,2

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iMac doesn't produce video signal after a system upgrade

I have a mid 2011 iMac which won't boot up following a CPU upgrade. The motherboard is receiving power and the first two diagnostic LEDs light when the power is turned on, but upon attempting to boot the system while I get a boot chime the screen remains black.

I suspect an issue with the video card, but replacing that did not yield anything different. After installing the replacement card I've attempted to proceed without installing either the video card heat sink or LCD panel (for testing purposes) as I supposed that the third LED would light if the motherboard was communicating with the card, even if the monitor remained disconnected and it wasn't able to output a video signal. The GPU does grow warm when the system is powered on (so it seems to be receiving power properly), but the third LED remains unlit.

Am I correct in the assumption that if the 3rd LED isn't lighting at this point there isn't much point in trying to hook the screen up, or is it contingent on being connected to a working screen? Assuming there isn't an issue with the replacement card I bought, what could be causing this?

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crwdns2933897:0crwdne2933897:0

I'm suspecting the CPU is not properly seated! You'll need to take it out and inspect the pins as often I see the socket pins bent.

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Thanks! I took another look at the pins in the socket and there are a couple that look as if they may be slightly out of alignment. Is that something I can fix with a pair of tweezers and an abundance of patience? Furthermore can I see if I succeeded by trying a brief power up (maybe 30-45s before cutting the power) and monitoring the chip temperature?

crwdns2934271:0crwdnd2934271:0crwdne2934271:0

@classicalfixes - VERY CAREFULLY! These pins can snap if you go to far bending them back.

There really is no point monitoring or limiting the power if you fail there's really no second chances here.

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Fortunately the pins weren't too badly bent and straightening the ones that seemed a bit out of alignment appeared to fix the problem. It at least got the third light working so I'm optimistic at least

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