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My 2011 27’’ iMac had a graphic card problem (vertical lines on the screen) I took the opportunity and upgraded the card from 1gb to 2gb. When I turn on the mac it start to boot and suddenly shuts off I can turn it back on again and it happens again and again. I tried to make NVRAM Reset and it didn’t help. I took out the power cord from the mac, waited few seconds, pressed the power button for 10 seconds, then, I pressed the power button and hold while putting back in the power cord and powered on the iMac. the fans started to run at full speed and the iMac is running good and stable without shutting down but the fans running at full speed. i made a SMC Reset, the fans started to run normally but the problem appeared again and the iMac shuts off. #1 led is turned on while the iMac is turned off 1,2,3,4 lets turned on after few seconds after the iMac shuts off #1 led is the only one on i made an hardware test while on “safe mode” (fans at full speed) and i got error code: 4VDC/1/40000003: VIDEO CONTROLLER any advice? Thanks in advance
Either you got a GPU card that doesn’t have the custom Apple firmware. Or, its’ defective. You’ll need to return it and locate the correct part which is this: AMD Radeon HD 6970 with 2 GB of onboard RAM - Apple P/N: 661-5969
I pull the plug in back and wait to turn imac on , it works then it downloads and picture comes on for 3 minutes and off automatically? whats wrong
