Chosen Solution
I replaced the power supply and still same problem. Turns on fine, then after about 5 minutes the screen freezes and then goes black. I hear the fans running. I replaced the power supply yesterday and same result. I’d hate to spend $485 on a new screen and that not be the problem. Is it a heat sensor? It’s only on 5 minutes or less. Any suggestions beyond the trash can?? It’s a late 2015 I7 full RAM Update (12/18/2021) Hi..Thank you so much for the reply.. Here is what I found..First, I can see no image on the screen at all after it freezes then goes black. As for the second suggestion, I hoked up my working iMac to the old one via ethernet cable and where I’m confused is in the finder part. I don’t see where to type in “Go>Network”..
The first test I would do is see if placing a flashlight on the screen at an angle allows you to see the faint image of your desktop and its icons. Are you able to see the image? If not, let’s see if the system is still running. Using a second Mac system connect the two systems back to back using an Ethernet cable. The working Mac should see the other Mac over the network connection. From the Finders menu bar Go > Network do you see it. If you know the user account & password you should be able to log in. Update (12/18/2021) This should help! First click on your desktop as we don’t want an active folder or drive then the Menu bar should show it!
Update (12/21/2021) @Bob - Take the display off, but keep the cable connections attached (use a block to hold the display so you don’t damage the cables)
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. What are they telling you when you startup and the display is working and watching as the display goes out??
