20" Intel iMac Power Up Problem

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Joined: Nov 6 2008
Posts: 4

I have a 20" Intel Core Duo iMac that only intermittently powers on. Sometimes if I plug in the power it will instantly start and work fine so long as you don't reboot it (it won't start back up). Other times it won't turn on, even if I push the power button, but after 5-10 minutes it will randomly turn on and again seem to work fine unless you reboot it.

I believe it is probably the power supply, but it doesn't look or smell like anything got fried on it. The part number on the PSU is 614-0378 (identical to this one) . When I plug it in and it won't turn on there are no diagnostic lights lit up. I also checked out the power with my multimeter on the 5-pronged connector on the PSU: the two black wires were grounds, the grey ones were giving out ~12V (it fluctuated quite a bit between 11.5 and 12.5), but I couldn't get any reading off of the brown one.

Does anyone know of a way to properly test the PSU? Does it sound like that is the problem or could it be something else? BTW, I already replaced the NVRAM/PRAM battery.

Thanks!

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Joined: Nov 19 2008
Posts: 4
Pesky, I also have a 20" iMac

Pesky, I also have a 20" iMac with the intel core duo and I'm having the same issue. I've guessed as you have that it be the PSU, but I am not for sure. It's been sitting for a few weeks until today when I decided I'd rather see if I can fix it rather then send it off and wait longer and possibly spend more than I need to. So I pulled it apart and took a crack at her...I tested the PSU as you did and got both blacks as the grounds and a fluctation between 11.7 and 12.3 on the greys, but nothing on the brown as well. Very similar results to yours obviously...I figured while I had it open might as well throw a new cmos (nvram/pram) battery in just in case. Hit the power button and bam, fired right up, went to the login, logged in and business as usual...or so I thought...I was trying to check some settings and such to make sure all was good when I got a kernel panic. So I reached for and held the power button, but it wouldnt restart/or shut off. So I killed the power to my APS and opened it back up, pulled the battery out again for 30 seconds stuck it back in plugged it in and bam fired right up again. I have done so several times now, as it keeps giving me a kernel panic. I have replaced the memory from the original 512mb to 2gb. However, I can only use one 1gb stick with the original 512mb stick. But my guess is if its not the PSU causing my problem that it is the OEM memory going bad as it would with a pc.

I have been scouring the internet for a couple months on this issue and so far you are the only other person to have the exact same symptoms I am having, please let me know if you find any possible solutions. I have a few other tricks I may try later, I will post again if I find anything worth while.

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Joined: Nov 6 2008
Posts: 4
Good to hear I'm not alone in

Good to hear I'm not alone in this. So I ended up getting another PSU off of eBay and it didn't change anything. I did make a minor discovery last night however. If I clear the NVRAM/PRAM when it boots (hold command+option+p+r before the Apple logo appears) I can then reboot it once it is up. I never got it to reboot without removing the battery and unplugging the power until I did that.

This makes me think the PRAM/NVRAM is just getting messed up somehow. I have tried putting the battery in while it is running, after I had cleared the PRAM/NVRAM, and it didn't make it any better. I'm going to try reflashing the firmware with the 1.7 firmware CD.

Can you give me some more info on your iMac? I'm not near my iMac right now, but I know that my model identifier is iMac4,1. I'll post more info (firmware version, etc) later.

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Joined: Nov 19 2008
Posts: 4
Well as I said, I tried a few

Well as I said, I tried a few other "tricks" or better known as trial and error...and I got it running. My solution - pulled open the case again and went exploring. I realized in the process of doing so that it wasnt so much the battery that was keeping it from starting, it seemed to be the fact of clearing the nvram/pram that allowed it to actually boot, but when i plugged the power cord back in it would come on. Which put me to mind of something shorting out.....So I removed the left speaker (facing the screen) and traced the cable from the power button to the logic board and are you ready for this?.....lol.........unplugged it for a second, then plugged it back in and viola! It worked to my dismay, but it worked. Now I dont know about you but I have had this ongoing issue for several months and was about to just come up with however much they would have charged and give it over to its maker. Wink But it was a simple button connection, I don't know if it will work for you as well, but I do hope so....This could explain why we seem to be the only ones with exactly the same symptoms.

20" iMac Core Duo - iMac4.1 (as well!) - SMC=1.f5 - Boot ROM Version:IM41.0055.B08 - with 2gb of crucial memory...ummm, any more info, let me know. But I hope this helps as ridiculous as this sounds, but it worked for me.

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Joined: Nov 6 2008
Posts: 4
I only wish...

Well, I had my iMac running all day in Windows 7 (via Boot Camp) and it was working fine. But of course when I went to reboot it into OS X (so I can burn that Firmware 1.7 disc) it wouldn't start back up. I tried your power button trick but it still won't come up. My NVRAM/PRAM may not have cleared yet though, it usually takes quite a while on my iMac it seems. It usually has to be unplugged with the battery out for _at least_ 30 minutes usually.

It looks like your info is the same as mine (even 2GB of Crucial RAM), but I'll have to check when I can get it to boot back up again.

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Joined: Nov 19 2008
Posts: 4
have you tried re-install osx

have you tried re-install osx since the issue as well?

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Joined: Nov 6 2008
Posts: 4
I haven't, but maybe I should

I haven't, but maybe I should try it. Do you know can I reinstall OS X without messing up my boot camp partition?

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Joined: Nov 19 2008
Posts: 4
I personally do not run Bootc

I personally do not run Bootcamp, I use VMWare Fusion. But from what I have heard from people and if it acts anything like windows, behind the scene, it shouldn't mess with it....The only reason I even mention the reinstall, is because I did have issues once I was able to boot (after doing the NVRam/Pram jig) but when I would reach the login screen OS X would lock up and the few times I was able to get in it would kernel panic me some more...It seemed as if the iMac had learned the problem and tried to adjust to it? I don't know but the reinstall went flawless and haven't had even a hint of an issue since all the aforementioned, as well as the reinstall...

Back to Bootcamp - I would say if you are really really worried with the Windows side of the partition, then back up your files or if you have the program (ie; Norton Ghost, Acronis Disck Image, etc) make a quick disc image.