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Hi, I have an iMac mid-2011 but won’t start. Here is the result : The iMac won’t start when I press the button, the LED1 is green but nothing append next. The only way to see something is to press the button and put alimentation, then, release the button and the fan (right) start to turn at maximum and 5sec next, the left fan start too but nothing else append (screen or whatever) Do you think the alimentation is dead or it’s the motherboard ? Thanks! Update (08/17/2020) Hi, I have tested the power supply and have the correct values on the rail, does that mean that the power supply is functional? or maybe when the motherboard starts up, the inrush current is too strong and the power supply does not follow? My values from DVM follows this :
Thanks!
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. Most of the time its the power supply that goes! The power supply offers more than one power service, so while the fan may power up the logic board may not. It’s also possible you have a short on the logic board some where. Sometimes the GPU board fails with a hard short. The only way is to diagnose this deeper is to use a DVM measuring the power supply and checking the power rails.
