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

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Computer won't boot if PSU is plugged into LCD screen

Hey all,

I'm trying to repair a late 2007 intel iMac 24", EMC 2134. I opened it up and checked the LED lights: they were all off. Because of this, I thought it needed a new power supply unit, so I ordered one on ebay and thought I was good to go.

Cut to this afternoon. I replaced the PSU, plugged in the appropriate AC in, DC out, and thermal sensor ports, but I left the LCD screen unplugged from the PSU. The computer boots fine, and all diagnostic LEDs are green. In fact, the PSU wasn't the problem at all - the old one works great. However, when I plug the LCD screen into the PSU, the computer is totally non-responsive, won't boot, and none of the diagnostic LEDs are on.

So I'm guessing something in the LCD is shorting out the rest of the computer. Is there a way to fix whatever individual component is fried, or do I have to replace the screen? And if so, does anyone know where I can find that part?

Thanks again!

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any chance you can find a manufacturers number or a model number on the panel? That would allow us to find a datasheet and we could check on that to see what might give you the problem. of course, do check your connector on the board, just to make sure that it is okay.

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You could use an Ohm meter to test continuity between the blades of the AC outlet on the back thru to the connector on the PSU. I would strongly not try to test this live (AC)!

It sounds like you have isolated this down correctly to the PSU. I would also point out you could have gotten an electrical spike (lightning) which killed it. Make sure you have a good surge suppressor outlet strip and/or a UPS for the system and your accessories are plugged into.

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The plot thickens! I ordered a new PSU, and as I was installing it I made a new discovery. When the PSU is plugged in to everything (the AC input, DC output, and thermal sensor I believe) *except* the LCD screen, the computer boots fine, and all 4 LED diagnostic lights are on.

However, if I plug the LCD screen into the power supply, the computer won't boot at all, and none of the LEDs light up. I know next to nothing about electrical engineering, but does this mean that the LCD is shorting out the rest of the computer?

Thanks again!

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Yes, and no. It sounds like it, and it is possible. Check your connector as well....

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