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

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iMac keeps Rebooting but LEDs and Voltage are fine

Hi guys,

I have an Early 2008 20 Inch iMac EMC 2210. When I start it up it will run for a short period of time, like about 10s-2min (used to be a bit longer but seems to have shortened over the last weeks were it was standing around). After that time it powers off and powers on again after a couple of seconds. Then it keeps rebooting all the time with about 2s on and 2s off till I pull the power cord.

I checked the diagnostic leds and they seem to be fine. All 4 leds light up after a while when I have the first 'longer' start. Then when it keeps rebooting the first LED remains ON all the time and the second also lights up shortly before it reboots again.

I also checked the voltage following the guide on this page. I have the correct voltages all the time. I noticed that I have 12V on pin 9 on standby while the guide says that i should have 12V on pin 8 on standby, so those seem to be switched, but it might also be described wrong in the guide?

I checked the AC/DC, SATA Power cable and it seems like I have an old cable, as i were not able to find a serial number on it easily. So it is NOT the new 922-8188 cable.

Do you think I need a new AC/DC, SATA Power cable, a new power supply or even a new logic board? Any ideas on how to solve my problem?

Thank you!

Mario

Answer this question I have this problem too

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I removed the Logic Board, cleaned everything as good as I could and replaced the thermal paste on the CPU. I did so by following the guides provided by ifixit.

Sadly the problem still exists. Keeps rebooting after a couple of seconds.

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3 Answers

LED #1 should always be on - unless the wall cord is unplugged, or, the PS is shot.

That it runs for two minutes seems to point to an overheating problem. On a box that old your thermal paste could be shot and need replacement… that's a major project.

I would clean out the inside of the machine… leave the back open and set up a small fan and see if it operates any longer… if it does after leaving it overnight you should run AHT and see if it identifies an overheat (or other problem).

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LED 1 is always on when the Power Cord is plugged in.

I guess i could replace the thermal paste and clean everything (did not look too dusty to me when I opened it up).

What do you mean by leaving the back open? I can not remove the back metal plate from an imac, can I?

I got the same issue when I had the front open and tried starting it.

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Too many different models I should have said "access door" not back.

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Well in this case...I had the box open but it did not really run any longer. It seems pretty random on how long it will run but when it was off for some time it will run a bit longer than if it was in use before.

I will change the thermal paste and clean the inside of the iMac and then report back if it helped.

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I removed the Logic Board, cleaned everything as good as I could and replaced the thermal paste on the CPU. I did so by following the guides provided by ifixit.

Sadly the problem still exists. Keeps rebooting after a couple of seconds.

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I had this happen one time with a computer and my power button was stuck i replaced it and it worked fine. Try unplugging the power switch and then starting it by jumping the pins. Also like the other person says a cpu overheating is the main thing that causes a system to shut down after starting up because the bios sees the cpu is getting too hot and doesnt boot all the way. Also if the cpu was shorted in some way it may do the same thing making you think it was overheating. Generally if you have a heatsink and fan on it everything is running and clean it shouldnt be turning off that quickly. With that said it should NOT power itself back on if that is the case i fully suspect the power switch or possibly even the reset switch acting weird too. Hope that helps if all else fails try reflowing the cpu and gpu thats your last effort i can think of.

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Okay well as long as you know the power button isnt a problem that is good. It still doesnt make any sense to me how it would power on by itself without something like a power or reset button having a fault. The power cables are another good possibilty but usually dont go bad just get loose and then short out the system so that is possible but really doenst explain powering on by itself that is the real confusing part. Now overheating is not going to be something you can see even with a magnifier and a lot of experience it can look perfectly fine and clean and still had an overheating issue that make a crack or something in the solder joint. Before anything i would have to advise you to try a known good power supply because even if the voltages are right something can be going on inside i really suspect that if it literally turns on by itself with you doing nothing at all because i just dont see any possibility of a bad cable restarting the system unless its just how macs do when they short restart instead of turn off but that really doesn't make sense. If youve exhausted all options seriously i would reflow the board i have done this with consoles graphics cards bad motherboards using a heat gun and had 100% success even though i know it sounds kinda weird. Everything i reflowed looked perfectly fine but all it took was a reflow and they work perfectly and instantly.

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As I replaced the thermal paste I would say that overheating is not the problem. All fans are running okay and I cleaned everything.

Also when I removed the logic board I had to pull the power button connector so I would also say that the power button is not the problem. I also think that there is no reset switch on the imac.

I still think it might be the AC/DC, SATA Power cable as that is the suggested part to change recording to the apple service manual.

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I have the same problem of rebooting at start up. Consistently, it happens after startup progress bar in Yosemite goes a fraction of an inch. Then it reboots. It's the same thing every time I do it. The only thing that prevents it from happening is if I disconnect the smaller SATA connector from the hard drive. That will prevent the restart.

I have tried very as hard drives with the same result. So this tells me that it is not the hard drive.

I have also disconnected the power button to try and troubleshoot it. I get to see results with our without the power button wire plugged in. I've tried other wall outlets and powercords. I'm down to swapping out the power supply, but I think I should wait and swap out the sata cable first.

Since that sata cable goes underneath the logic board, I would have to take out the board, Instead, I want to try and just run a new sata cable over the top of a lot of board between the hd and the board down at the bottom where it connects. That way I don't have to take out the logic board.

Any thoughts?

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