Won't boot, black screen

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iMac Intel 20" EMC 2133 and 2210

Model A1224 / Mid 2007 and Early 2008 / 2, 2.4, or 2.66 GHz Core 2 Duo processor

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Xavier Cherel @xaviercherel

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Posted: Jan 9, 2013

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Won't boot, black screen

I got an iMac 20" Intel duo Core of early 2008 (A1224).

It was running fine until 2 months ago : I got three times chime, white screen with the wheel running and fourth time black screen, no wheel, no chime.

With the help of Ifixit tutorials, I opened the iMac and observed the diagnostic LED's while pressing the On button :

LED 1 is on, LED's 2 and some time 3 go on and then the iMac shut itself Off and recycle.

LED 4 never goes On.

I disconnected the data display cable of the internal LCD and then I could hear the iMac doing the full boot sequence, chime and three first Led went On in sequence and stayed On.

Then I removed the internal LCD and plugged in an external Screen.

I recovered all the functions : iMac works perfectly.

Only LED 4 is off.

This would mean that Video Board is OK and that Logic board versus external display is OK. But the Logic board does not "see" the internal LCD display (Led4 off).

Yet I dismounted the Video Board and passed an air soldering gun on the video chip. Remounted the whole thing. Same result : iMac does not see internal LCD.

I tested the Power Supply voltages according to iFixit values. I got differences :

First on my power supply pins 2, 7 and 8 are on the same track as per Ifixit photos of the PSU, so they read all the time the same value, which is different than the table of Ifixit. By the way, this table should be corrected as per the photo.

Secund, Pin 5 on Standby reads 2.7 instead of 3.8V, but goes to zero in the On mode. Yet the standby mode is working properly. Is this value critical ?

Without the internal LCD, I tested adding car front light bulb between pins 1 & 2 (12V) of the PSU (55 watts) in the On mode to verify that the power supply could handle extra power. The PSU handled the extra load and Mac stayed on.

Is that enough to stop suspecting the PSU board ?

I tested the data display cable plugged to the logic board without the LCD on the other end. The iMac works fine.

I tested a different LCD internal display. Mac will not boot as with the old LCD display.

I replugged all cables of the LCD, but disconnected the Inverter from the power supply. Mac will not boot.

Tested a new inverter, Mac will not boot.

I then dismounted and cleaned the Logic Board and looked for damaged caps : all good.

Remounted the iMac : always the same thing. It will not boot on the internal LCD, but does on an external LCD.

Now, I am a bit out of ideas.

Changing PSU or Logic board is a lot of money.

That iMac machine is a wonderfull computer when working. Before buying a new one, I shall be very intrested to find the schematic of the Logic Board and its connections to the internal LCD.

Could someone help me ?

Has someone any other idea to test ?

Answered! View the answer I have this problem too

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Thanks for your answer and your search.

By the way my iMac is the 20" Core 2 Duo 2.66Ghz.

I ordered the new LCD at Micropuces.com by part number, i.e. M201 EW02 because it was the original part number and manufacturer.

It looks like the Powerbookmedic ignores AU Optronics.

I agree though, it was a refurbished one because new one is too expensive.

Do you know wether the internal LCD is just connected in parallel of the external one ? This is why I am intrested in schematics.

Yet one thing still strikes me. If I don't plug the data display cable in the logic board, i.e. the Mac boots up and is running, why does it not light up the neon bulbs of the original or the new LCD display at the same time it lights up the external display ?

Because too much money is involved here, I shall open the original LCD display and keep you informed.

Jan 9, 2013 by Xavier Cherel

I worked on the logic board resoldering few points and passing the Intel logic processor to the warm air soldering iron.

I put apart the original AU M201EW02 LCD display and notice that the 4 kapton multiflex cables were not soldered to the LCD Pcb but just pressed against the very small gold tracks of this Pcb.

I then arrange so that in reassembly there was a foam tape pressing the flex cables against the Pcb;

After reassembling the whole thing IT WORKS !!!

I can't tell which is what, but eventually it works.

Thanks to the ifixit community, guides and people.

Jan 12, 2013 by Xavier Cherel

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Puru @purus

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Posted: Jan 9, 2013

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Replace your display with a correct part. I've searched one for you that exactly fits yours. And by the way, your iMac is not Core Duo but Core 2 Duo. Either it's of 2.4GHz or 2.66GHz model. Check the part here and copy the part numbers. You can buy from anywhere else but get the correct part number. Otherwise, it won't display anything. Your iMac is just fine. Only the display is dead. Don't work out too much. Simply replace a good known display part.

The link is here for your reference:

http://www.powerbookmedic.com/Intel-iMac...

If you like this, please rate it. Thanks.

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Thanks for your answer and your search.

By the way my iMac is the 20" Core 2 Duo 2.66Ghz.

I ordered the new LCD at Micropuces.com by part number, i.e. M201 EW02 because it was the original part number and manufacturer.

It looks like the Powerbookmedic ignores AU Optronics.

I agree though, it was a refurbished one because new one is too expensive.

Do you know wether the internal LCD is just connected in parallel of the external one ? This is why I am intrested in schematics.

Yet one thing still strikes me. If I don't plug the data display cable in the logic board, i.e. the Mac boots up and is running, why does it not light up the neon bulbs of the original or the new LCD display at the same time it lights up the external display ?

Because too much money is involved here, I shall open the original LCD display and keep you informed. — Xavier Cherel
I worked on the logic board resoldering few points and passing the Intel logic processor to the warm air soldering iron.

I put apart the original AU M201EW02 LCD display and notice that the 4 kapton multiflex cables were not soldered to the LCD Pcb but just pressed against the very small gold tracks of this Pcb.

I then arrange so that in reassembly there was a foam tape pressing the flex cables against the Pcb;

After reassembling the whole thing IT WORKS !!!

I can't tell which is what, but eventually it works.

Thanks to the ifixit community, guides and people. — Xavier Cherel