iMac Intel 27". EMC 2309 (Late 2009, Core 2 Duo 3.06 or 3.33 GHz), EMC 2374 (Late 2009, Core i5 2.66 GHz or Core i7 2.8 GHz)

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Is the GPU dying?

A few months ago, my iMac suddenly shut down, and wouldn't turn back on. After getting it checked and serviced, I was told that the Logic Board(?) was dying. However the Mac still can boot, although the screen wouldn't turn on unless I manually restart the Mac around 2-4 times.

According to a forum, it's caused by a failing GPU. Apparently it can be "fixed" by basically reflowing the solder. I don't want to take the risk of damaging the card by heating it up, however, so I wanted to know. Is this actually caused by the GPU?

If it's the GPU that is failing, I have plans replacing it with a newer Radeon 6xxx card.

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First take a look at the diagnostic LEDS and tell us what you find:

LED 1 - Indicates that the trickle voltage from the power supply is detected by the main logic board. This LED will remain ON while the iMac is connected to the AC power. The LED will remain on even when the computer has been shut down or put to sleep. The LED will turn off only if the AC power is disconnected or the power supply is faulty.

LED 2 - Indicates that the main logic board has detected proper power from the power supply when the computer is turned on. This LED will be ON when the computer is turned on and the power supply is working correctly.

LED 3 - Indicates that the computer and the video card are communicating. This LED will be ON when the computer is communicating properly with the video card. If LEDs 1 and 2 are ON and you heard the startup sound, but LED 3 is OFF, then the video card might be installed incorrectly or need replacement.

LED 4 - Indicates that the computer and the LCD display panel are communicating. This LED will be ON when the computer is turned on and video signal is being generated. If the LED is ON and there is no image on the LCD display panel, the LCD display panel or inverter might be installed incorrectly or need replacement.

Next hook it up to an external monitor and see if you get a signal to it. If, indeed the GPU is failing, it will also fail on the external monitor. It the monitor is good but your internal display is bad, then we need to look further up the chain.

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Sadly your caught between a rock and a hard place :-{

Yes, your symptoms are inline with a GPU failure. In truth it’s the leadfree solder used to solder the chip which is the failure not the GPU chip it’s self in most cases.

What has happened is the constant heat has slowly altered the Tin from a conductive material into a semi-conductive crystal form. The correct way to fix this is to carefully remove the chip and clean off all of the old solder and apply fresh solder (some with Lead hopefully).

Reheating the GPU card can buy you a bit of time but it’s not a long term fix as all you’ve done is reflow some of the solder back into a conductive state. But as the solder still has crystals within it, in a short time the solder will once again recrystalize back.

If when you were a kid you made rock sugar by dangling a thread into a glass which had a high concentration of sugar water the sugar would build up crystals on the thread. If you remember it took a bit of time for it to start but once it did it, didn’t take much time to build up. That’s the same process here, just with Tin.

So the other option is replacing the GPU card with a new one if you can find it. Must today are from used systems and are costly!

If you can find someone with the proper gear the clean off the old solder and re-ball the chip that would be the better solution.

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