Video circuitry on logic board functional.Ĥ. Verify if image appears on external display when system is booted. Verify system functionality and return to user or go to appropriate troubleshooting flow.ģ.
Verify if image is visible on built-in LCD panel, with adjustable backlight level.
(Reset SMC and clear PRAM if necessary for proper boot up.)Ģ. Verify boot chime present and fans running when computer powered ON. Then after assembling and connecting it to power after some presses of the power button it started normally on the main internal screen and the external monitor as secodnary (ISSUE FIXED :) :) ).I'd start by following Deep dive suggestions from Apple but would stop at #7ġ. I did the same thing and changed paste on both the CPU and GPU.
Sometimes on my pcs I use to repair, if they are old enough and have higher temperatures I change the thermal paste and are working very smoothly. I disassembled the machine and got out the logic board using instructions from ifixit. Running it I saw temperatures around 30-40 deg C and the ODD and CPU fans at more than 4000. Then booted with the displayport and searched and found the TG Pro. I also tried with this configuration pressing D at the boot to go to diagniostics but nothing was showing on the second monitor. I tried with external monitor in mini-displayPort and after 1-2 restarts it started on the external monitor I checked in the internet from another computer and saw many different causes for black screen. Restarted many times but the screen always. After the restart the start sound was ok but the screen black and the fans at full speed. Today morning when I was checking sites in Safari, the whole screen went white and the iMac restarted. Symptoms: The last months fans run at full speed. This LED will be OFF when the computer is turned on and running at the correct temperature. LED 4 Lights only if the computer detects an over-temperature condition. This LED will be ON when the computer is turned on and video signal is being generated. LED 3 Indicates that the computer and the LCD display are communicating. This LED will be ON when the computer is turned on and the power supply is working correctly. 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 off and your power supply is working correctly. LED 1 Indicates that trickle voltage from the power supply has been detected. You'll find them just to the right of the memory slots, and sit behind the SATA cable where it comes out of the connector. Bummer! You'll need to open it up to check your cable and locate the diagnostic LEDS to see what they tell you.
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