Model A1225 / Mid 2007 and Early 2008 / 2.4, 2.8, or 3.06 GHz Core 2 Duo processor

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Screen went suddenly black, now fails to boot.

Hello

This iMac has given me absolutely no problems or symptoms of distress until last night when with no warning the screen went black and became unresponsive.

I hard reset and unplugged for a couple of minutes to let anything that might be a problem sort itself out, but now when powering on it cycles through grey apple screen with normal loud chimes and rotating clock hands, I can hear the drive spinning and the fan sounds normal. Then the screen goes black and the cycle starts again.

Holding down normal resets for PRAM etc all seem to have an effect, i.e. stall the cycling, but when the keys are released nothing changes and the same cycling resumes.

From my reading on this problem so far I understand that it may likely be one or more of the following problems...

1) power supply

2) logic board

3) graphics chip

Being out of AppleCare by just over a year is galling, and I understand that this isnt going to be cheap if I take it to an authorised service centre or apple themselves. I am more than confident to open up the case using the comprehensive guides on this site but would love some advice as to in which order I should attempt to diagnose, check the above possible problems?

If I get the parts to check the power supply first would this seem sensible? Or would other users think it more sensible to send it to Apple to get them to diagnose the problem and then take the machine back and do the actual repairs myself?

Many thanks for your time and any help

Cheers

Tim

Update

Been a while coming but finally got the power supply repaired. Now I have 4 diagnostic LEDs lit but the system will still not boot. I have generated a USB boot drive but it still won't boot from this. No other method of booting works either (safe, recovery, verbose).

Is my only option to wipe the drive and reload the OS? I dont understand how this will help. If it won't boot from the USB drive then why would it boot from a new iOS?

Any more help gratefully received!

Cheers

Tim

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since you can see the grey apple on startup, my bet wolud be that GPU is ok. more likely it would be PSU i think - probably the big electrolytic capacitors, that would be the first thing i would go for. If you have soldering skills or someone who has, Try it as the first, relatively cheap fix - note that the electrolytic capacitors must be same capacity and same voltage and low-ESR types

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Thats brilliant thanks for the advice. I think I will go ahead and remove the PSU and see what Im dealing with first. Then see if I go for the capacitor option, or just replace it all. Cheers

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I would assume a SW problem before a HW problem.

Sometimes the issue is as simple as a corrupted kextcache, and you can fix that by booting with the shift key down. (This boot will take a LOT longer than usual. That's normal.)

If that doesn't work and you are running Lion or Mountain Lion, can you successfully boot of the recovery partition (boot holding down command-R)? Or can you successfully boot off the CD that came with the iMac?

If booting off a foreign source works, then the obvious first thing to do is run DIsk Utility on the boot partition. If that reports a problem and fixes it, try to boot again. If it tells you there is a file system problem that can't be fixed, Disk Warrior (which costs some money but is worth it) may solve the problem. Otherwise, worst case, try to re-install the OS (I assume you have a Time Machine backup) and maybe that will help.

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Tim will be eternally grateful.
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