Chosen Solution
As I was working on my Mid 2010 27” iMac, the screen changed with strange graphic artifacts. I shut it down and after a min when I tried to power it back on again it just wouldn’t start. When I pressed the power button I could hear the fans starting to work but after 5secs they stoped. No chime was heard, nor would the iMac boot. Screen remained black. I was working with High Sierra. Maybe I’m lucky that I got a TimeMachine backup, but I have no clue what my next step can be… I’m totally lost ? PS: Supposedly if I buy a new, up to date iMac, can I use the TimeMachine backup I have from High Sierra system to restore my old iMac stuff on the new system? Update (09/06/2021) I did a few things: Removed the Display and GPU (Didn’t remove the GPU temp sensor) Did a PRAM resetFans worked at high speedHeard the Chime once Then I placed the GPU back and at boot there was a continuous chime. Strange because if its the GPU causing the continuous chime, why wasn’t it there in the first place, before I opened the iMac and before I removed/connected the GPU?
Yes, your TimeMachine backup will still work with a replacement system. But! Depending on what Apps you currently have you might have issues as the newer Catalina and newer won’t run 32bit apps. You might want to look for a used Intel Mac to replace yours Update (09/07/2021) Is it Christmas! The light you are seeing though the RAM slot area are from the onboard diagnostic LED’s. Most of the time they are covered!
And here’s what they look like and ID’ed
And 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.
