Chosen Solution
Try this: Turn down the displays brightness to the lowest setting that you can still see the desktop. Do you find the system is now staying up or running longer than before? If you do your display has a problem.
LED 4 indicates that the iMac is detecting over temperature conditions That is not correct on this model of iMac: LED #1 (left-most) Indicates that the trickle voltage from the power supply has been detected by the main logic board. This LED will remain ON whenever the iMac is connected to a working AC power source. 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 source 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 (right-most) 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. Did you ever get that machine to work?
The location you describe as hot is where the psu sits. Try to take it to someone who can test all the voltage rails, maybe something is gone bad. I had an similar problem on a late 2009 27" i5 iMac, but we figured out that GPU overheating was the cause (this machine shuts down when the gpu die hits 80 degrees Celsius).
Do you heasr your fans kicking on….. if not, change the fan!
I’ve ran into the same problem with my 24 inch iMac but come to find out the problem was with my video card. After the card started getting hot it would shut down my iMac . this is pretty common with iMac MacBook pros laptops there’s two ways to fix it. One replace the video card which can be expensive or two reset the video chip on your video card . That will require you to bake the video card for about eight minutes at 350° if you’re not technically inclined with breaking your Mac down I would not attempt it.
Go back to pc. I have been a mac fanboy for 7 years and since the death of Steve Jobs apple has been living off its former reputation and Iphone. No new next big thing , quality has gone down hill , no touch screen, even customer service is not what it use to be. I am going to give microsoft another try . I tried a friends 27 inch HP envy and was very impressed.
It seems to me that you may have a defective temperature sensor in your machine. LED 4 indicates that the iMac is detecting over temperature conditions, which are caused by dusty vents (ruled that out) or defective temperature sensors. During normal operation, LED #1 #2 and #3 should be on, and LED #4 off. You will want to go through the iMac and make sure that all the temperature sensors are properly connected and are not damaged. If the problem persists, then you will need to get a set of replacement temperature sensors. You can usually find sets on eBay or amazon for pretty cheap. Hope this Helps
