iMac won’t start

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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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Alexis Martin @alexismart40142

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发帖于: 2020年8月11日

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iMac won’t start

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!

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!

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Did you replace the power supply?

由 Dan 完成的 2020年8月11日

No, I want to be sure if it’s the power supply or the logic board. The thing is that I can power on fans with the method I have write in my comment, so the power supply can be dead even the fan run?

由 Alexis Martin 完成的 2020年8月11日

Time to replace the GPU board!

由 Dan 完成的 2020年8月17日

Can I remove the GPU and start the computer ? Does it start ? Just to confirm that’s the GPU

由 Alexis Martin 完成的 2020年8月18日

Okay update! So I have removed the GPU and tested to start the Mac without it, and it works! So it’s the GPU.

Is the baking method is a good idea ? I see that we can replace the GPU by better card, is it a good idea or just buy the same GPU ?

Thanks!

由 Alexis Martin 完成的 2020年8月18日

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No, I want to be sure if it’s the power supply or the logic board. The thing is that I can power on fans with the method I have write in my comment, so the power supply can be dead even the fan run? — Alexis Martin
Can I remove the GPU and start the computer ? Does it start ? Just to confirm that’s the GPU — Alexis Martin
Okay update! So I have removed the GPU and tested to start the Mac without it, and it works! So it’s the GPU.

Is the baking method is a good idea ? I see that we can replace the GPU by better card, is it a good idea or just buy the same GPU ?

Thanks! — Alexis Martin

Dan @danj 声誉积分: 478.9千 Self employed contract worker 35 329 970 · Answer 1 · 2020-08-11T17:18:47-07:00

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.

iMac Intel 27" EMC 2429

iMac won’t start

Update (08/17/2020)

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