Model A1225 / Early 2009 / 2.66, 2.93, or 3.06 GHz Core 2 Duo processor

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Won't turn on with display panel connected

Just wondering if you can help me to figure out the problem with my iMac.

It tries to turn on but shuts down very fast as soon as it tries to turn on display. I opened the iMac and when I connect the power cord first LED of the Logic board turns on. When I press the power button second and third LED turn on. Then computer shuts down as soon as it tries to turn on the display. I disconnected the display backlight cable from the PSU and computer turns on with no problem without backlight. Then I decided to reconnect backlight cable to PSU and computer turns on without any problems. I used the computer for 2 days. I shut it off and on for several times with no issue. The problem starts again when I don't turn the computer on for several hours. Then I must to the same steps again to push it to work.

Do you think that it's PSU problem?

Thanks a lot

Answered! View the answer I have this problem too

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See if when yo put in target mode the system still shuts down. If is does then it's the PSU.

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Thank you very much Dan,

I don't have the cable to put it in target mood. But when I discount the backlight cable and connect it to an external monitor through mini display port it works fine.

It should be either PSU which can not supply enough power or LCD which uses a lot of power. But the confusing part is if I turn on the computer without backlight and turn it off and reconnect the backlight again it works fine until I keep it off for a long time.

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You don't need to connect a cable just to see what is happening here. The idea is to isolate out the CPU logic and the OS. Is the system stable at that point? Then using a second Mac connected run Disk utility on your systems drive to make sure its in good shape via Target mode.

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System is totaly stable without backlight.

And it's totaly stable with backlight after I reconnect the backlight cable.

I will do that tomorrow morning and let you know.

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I tried target mode. It does same thing.

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It's working again by replacing the power supply.

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