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iMac 27 A1312 ECM 2429 I purchased an iMac 27 2011 not working. Was told that it wouldn’t turn on so they purchased a new iMac and had Apple take out the HHD. I replaced the HHD and power supply and ran the LED test. #1 lights up only. Do I need a new logic board and is it worth it for that iMac? My iMac is a mid 2007 and thought this would be an upgrade because its a 2011.
All that #1 LED indicates is that the power supply is receiving trickle power. Replace the power supply. Here’s how: iMac Intel 27" EMC 2429 Power Supply Replacement Here’s the part you need: iMac Intel 27" EMC 2309, 2374, 2390 or 2429 Power Supply UPDATE 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.
FIXED! I finally found someone else who had fixed a dead iMac of the same vintage just by replacing the video card. And since I’d already replaced virtually every other part of consequence, it sounded like I might have a good chance of success. So I jumped… And it started right up! Never been so happy to hear a BootBong! It’ll take me awhile to get a working system to my liking all loaded in, but so far, so good. Also found that the replacement motherboard was indeed new… no serial number! Found and implemented “Blank Board Serializer” (an Apple service utility), loaded the old serial number, and off to the races. So, now I have a virtually new 2011 iMac; only the LED Backlight Board, DVD Drive, and Display are left. Well, cabling, too. Plus, I have an original power supply, and the original Ci7/3.4 GHz motherboard as replacements if necessary. The new motherboard was the Ci5/3.1GHz model, and the replacement graphics card was the 6750 rather than the failure-prone 6970 that came with the machine new. I seriously doubt I’ll miss the extra power those old parts came with; I play few games these days. I also put a new SSD in to Boot, so that helps to speed things back up.
I forget but does the iMac have a battery? the PRAM battery can mess up a Mac. Rest PRAM and also Power Manager and see if that helps. you changed a lot that involve those 2 and it may just fix it. Mike
I have a similar problem with my mid 2010 i5 - 2,8GHz - 27inch iMac. It does not power up. I checked the 4 LEDs. When I disconnect the power cable on the back and then put it back on one (!) LED is lighting up once (!) and then goes off again and shortly afterwards lights up a second time but then no LED is lighting up and the power button does not do anything. I can’t see which LED it is because the board is still in the housing but I suspect it beeing the first one. In the technician’s manual it sais that LED 1 should light up steadily if connected to power. What could it mean if the LED just lights up twice shortly? EDIT: I just measured the pins on the logic board according to the technical document. I have 12V between pin 1 and 4 and i have constantly about 3V between pin 1 and 12. So, when pressing the power ON button pin 12 is not changing - it is the same when pressed and when not pressed. I then have nothing on pin 11, where the button is pressed or not pressed at all. I am a bit confused because 12V on pin 4 should also make LED 1 light up constantly, which is not the case. And even if I disconnect the power button from the logic board I still have 3V on pin 12. Update (12/27/2017) I swapped out the logicboard and this solved it.
I’m having the same problem with the same imac I have. Took it to a computer store, they took it in the back, came back and said, “it’s the logic board”, and it would cost me about $500.00 dollars to replace it, it’s no good, just throw it away. The power supply is powering up, and working fine. I have tried steps #1 #2, and #3, and I don’t see any progress from trying them. It still won’t boot up, and the screen is still blank. The fan is turning and the power supply is working fine. What should I do? Trash it, or keep looking around until I find a solution?
