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

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iMac Powers on then off, then on again no display?

I bought this iMac sometime back second hand. It worked great for while, then it got to be, that every time you wanted to use it, you had to reset the SMC (unplug it for a while & then plug it back in) Recently it has gotten worse.

Now when you turn it on, the first 3 lights on the logic board come on, then immediately lights 2 and 3 go off, then they all 3 come back after a few seconds. All 3 lights again are on and all of the fans are running at normal speed. There is no chime sound & nothing comes up on the LCD. I have hooked a keyboard to the iMac, attempting to reset the PRAM, however it still does no make a chime sound, I do know the usb is working because the mouse lights up when plugged into that socket. I am inclined to believe this is a bad logic board. Luckily I have several of these units and I changed out the power supply & lcd for testing purposes, same result. Curious to know what symptoms are usually present with a bad logic board. And more specifically, is there a component within the board that could be the culprit? Thanks

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I bought a Mini DVI to VGA adapter for testing purposes, and nothing is displayed on the screen, thought I would mention that. I also checked most of the capacitors (some are not so excusable) they have 12 volts running through them, so everything seems to be normal. At least from what I can tell.

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The voltage to the capacitors is really not the point to be tested. Capacitors need to be checked for capacitance, not continuity. Just because you show 12Volt on them does not validate their function.

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I would start off replacing the PRAM battery here, it's due. Here's the IFIXIT guide: iMac Intel 20" EMC 2133 and 2210 PRAM Battery Replacement.

To test your Power Supply follow this IFIXIT guide: Technique: iMac Intel 20" EMC 2210 Power Supply Output Voltage Test.

If you find the Power Supply is gone follow this IFIXIT guide to replace it: iMac Intel 20" EMC 2133 and 2210 Power Supply Replacement.

From your symptoms its hard to tell if you have just a bad PRAM battery and/or need a new power supply.

iMac Intel 20" EMC 2133 and 2210 Power Supply Image

Guide

iMac Intel 20" EMC 2133 and 2210 Power Supply Replacement

Difficulty: Moderate30 minuten - 1 uur

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Thank you Dan for the advice.......I replaced the battery in the PRAM, with a brand new one, however nothing changed. So I proceeded to the voltage check, which I also did yesterday per the guide.

I checked the voltage with my volt meter per the outlined guide & everything appears to be right on spec. So I am at a loss. I have tried to find a schematic for this board layout pertaining to power, but have been unsuccessful. My guess is this going to point to the logic board, but I am not certain.

Thank you Old Turkey as well, My meter isn't advanced enough to check the capacitors. I did visually inspect them, none appeared to be leaking or bulged, they all felt nice & snug as well.

I may ultimately have to replace the logic board, but I was attempting to do all that I could to try and revive this one. Obviously someone has the ability to repair these boards, I see refurbished boards listed for sale on eBay. Hopefully one of them sees my post & has further advice. Any more ideas would be well appreciated.

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mmm ... I'm still leaning to the power supply as the issue given your symptoms. Try this: carefully put your system in a plastic bag and sickout as much air as you can, place the system in your refrigerator for a few hours (don't let is stay more than 3 hours!). As soon as you pull it out try starting it up still in the bag. Does it stay running longer or does it not start up at all?

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Ok, it has been several days. I tried the trick with the freezer (However my whole iMac won't fit into a freezer, so I tried the power supply, still no luck. I did buy a logic board on eBay for $29.95 guaranteed to work, I figured it would be a minimal investment to rule out the logic board. Anyhow, I got the board in & installed it. Final result PRESTO! the mac is back to working. I would like to refurbish the original board to be used again at some point. Call it a pet peeve or what have you, but the non matching serial numbers does sort of aggravate you somewhat. However I guess if you look at like a classic car with a cracked block, it would too, never be complete matching numbers machine again, so maybe I will just have my daughters enjoy the minimal investment.

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