Chosen Solution
Hi I have an iMac 27 EMC2429 A1312 core i5 16GB Radeon 2GB, mid 2011 for 4 years (2nd hand) powered since I own it through an UPS. Last week, all a sudden,I get a full white screen while surfing on the web (after 30min). I had to shut it down by holding the power supply button for 5 sec and …. it never started again :( For my iMac 27, the symptoms are now: black screenno chimethe fans run slowly, HD turns, DVD startsLed1 is on and Led2 turns on when push the start button.nothing moreOf course I tried all the basic steps suggested like resetting the SMC, the VRAM … and all you can find on this website: no change I brought the machine to a non-Apple repair center and 2 days later they told me that the mother board is on defect.. How to be sure ? If confirmed, should I also change the CPU itself ? and what about the graphic card ? and the PSU ? It seems Leendert faced the same symptoms than me. For him the graphic card change was the answer (not the Mother bard) . So now I’m confused and I’d like to have you opinion before looking on eBay Note: my iMac is unfortunately concerned by the VideoCard issue but had not been replaced by Apple (who extended exptionnaly the warranty for this series…but the previous owner of this machine didn’t do it) So far I never faced the video issues symptoms. Note2: I used smcfancontrol for 4 years that forces the fans at a higher speed than usual to be sure it will not be too hot (bad experience with my previous Imac24 where -also- my video card burnt) So now the question: changing the MB, the video, the PSU ? I am scared to loose money. If someone can help :) Thanks Patrick
You’ll need to pull the display off to see the on-board diagnostics LED’s on the main logic board. Here’s the guide you’ll need to follow: iMac Intel 27" EMC 2429 Display Replacement
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. Let us know what you see when you power up the system with the display off.
