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Hi, I replaced my Late 2012 21.5” iMac’s HDD with a Samsung 860 QVO SSD. Even after I had watched guides on YouTube I managed to fail. :-( Unfortunately, I made some mistake and now my system is not starting. I hear the chime, but after that the screen is blank. I get not signal with external display either. Is there a way to troubleshoot if the logic board is broken? Or is it only the screen? Thankful for help.
Hi , from the info supplied ! if the computer was 100% working before changing the hard disk , then check the display cabe behind the screen if it is plugged proper or damaged , as it is bit short and u need to take care on opening and closing if that all ok , then see the graphic card please let me know why did u change the hard disk ! all the best
On the logic board are four onboard diagnostic LED’s which can give you some clues
Here’s a breakdown of the onboard diagnostic LED’s: 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.
