iMac doesn't boot. Only left LED on Logic Board is lit

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iMac Intel 27" EMC 2429

Model A1312 / Mid 2011 / 2.7 & 3.1 GHz Core i5 or 3.4 GHz Core i7 Processor, ID iMac12,2

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Benjamin Luman @lumanbenjamin

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发帖于: 2016年6月7日

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iMac doesn't boot. Only left LED on Logic Board is lit

My Mid 2011 27" iMac EMC 2429 will not boot. The display doesn't come on, out of the 4 LED's on the Logic Board, only the 1st LED lights up, the other three are not.

My question is, I know it's not the PSU because the Logic board recognizes that it's getting power. Could it potentially be a failed Logic Board? and what does it cost to get it replaced?

Upon further inspection:

Removal of LCD screen. When powering on, there is some noise of noise activity from the PSU. No other activity seen or heard from other components. Upon holding the power button for 5 seconds, sequencing a hard shut down of the system; the noise level of the PSU drops from a 5 to a subtle 2. Upon further inspection of the PSU, there is an white-ish discoloration around the border of the unit (shown in pictures).The middle of the unit, excluding the border has a glossy, almost oily presentation.

Upon testing voltage of Pin 11, we have a 12.01V reading on the voltmeter.

No voltage reading from Pin 4.

Coin battery voltage measures at 3.0V.

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score 3 · Answer 1 · 2016-06-07T11:36:00-07:00

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mayer @mayer

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Incorrect logic, all you know is that the power supply is getting trickle power.

Start with the power supply.

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.

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Can you elaborate "Start with the power supply?"

由 Benjamin Luman 完成的 2016年6月7日

Read what the #1 LED being on indicates. Then here's the guide for replacing the power supply:

iMac Intel 27" EMC 2429 Power Supply Replacement

You'll need one of the following Apple power supplies (all will work)

Apple Part #: 661-5310, 661-5468, 661-5972

This one has a lifetime warranty: iMac Intel 27" EMC 2309, 2374, 2390 or 2429 Power Supply

由 mayer 完成的 2016年6月7日

I updated the post with some more information.

由 Benjamin Luman 完成的 2016年6月9日

Order in a power supply, install it. If it fixes the problem, you're in business. If not return it. It certainly looks like it has had some trauma. Power supplies can also partially fail. I've seen just the power to the hard drive fail or the hard drive work and the power to the logic board fail.

On this machine the most common failure was the GPU, thus this recall:

https://support.apple.com/en-us/HT203787

由 mayer 完成的 2016年6月9日

Does iFixit allow returns if the item has been installed?

由 Benjamin Luman 完成的 2016年6月9日

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Marcus Nash @nashfunk 声誉积分: 25 2 · Answer 2 · 2016-09-08T09:03:40-07:00

Marcus Nash @nashfunk

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I'm curious how this worked out. I am in a similar situation. I'm prepared to buy the power supply (have it in my cart now) but worried it's not the fix. I too have only the first LED lit, but I have no sound whatsoever.

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Hey. I'm the original poster here. I purchased the power supply, installed it, and nothing changed. Went ahead and returned the power supply unit for $10 shipping back and a restocking fee.

Went ahead and just sold my iMac as is. Didn't have the time or money to keep trying to fix it.

Sorry for the late reply.

由 Benjamin Luman 完成的 2016年9月9日

I also purchased the power supply, installed it, and nothing changed. Debating my options now.

由 Marcus Nash 完成的 2016年9月13日

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iMac Intel 27" EMC 2429

iMac doesn't boot. Only left LED on Logic Board is lit

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