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Random Shutdowns

C

c.pentasuglia

macrumors newbie
Original poster
Oct 21, 2011
9
0
I'm not sure if anyone will be able to answer this question, its kind of a tricky one. I have an IMac its an early 2008 Core 2 Duo 2.4Ghz, with 4 gigs of memory. Recently i was working on it and the screen went black, i was attempting to figure out what was happening and finally i narrowed it down to the fact it would randomly shutdown then try to restart, in most cases it would just keeping trying to restart, like i would hear the disk drive and fans starts, then a second later before it even could it would try to restart again. I have recent the SMC by unplugging and holding the power button for 5 seconds or so. After doing this the computer will start up again without falling into that loop of restarts it did before, but eventually it will do the same thing again. I have even tried to boot to my Windows 7 partition, but eventually it still just shutdown and tried to reboot. It seems to me it either has to be a firmware/kernel level problem, or a physical hardware problem. I was mainly wondering if anyone else has ever run into this problem, also i have checked all the temp levels on the computer in the few minutes it runs, and they all look acceptable. Oh and as a side note if i boot it up after resetting the SMC and it works for a bit, if i do put it to sleep manually it will sleep, but the second i try to take it out of sleep by hitting a button or moving the mouse, it just restarts again. This leads me to believe it has to be related to the monitor? Any suggestions or info will help, and i have gone though all the simple steps of resetting the pram, and SMC. So those help for a few then it will crap out on me.


Thanks Much!
 
The facts that an SMC reset makes a difference combined with the sleep failures point to a bad logic board, but it could still be a bad power supply, where removing power brings it back momentarily.

It's not going to be the LCD. It's not going to be the kernel (since you said it fails in Windows, too). It's unlikely that it's a temperature-related issue.
 
Thats what i figured

Obviously I'm hoping it's not the logic board... If opened it a few days ago, but i didn't feel like taking the screen out. So i was just checking for dust and such but i did not check the power supply. Could an imploded cap or dust on the supply cause it to fail? I know with macs imploded capacitors are the main reason they fail. Also as a side note if i wanted to rule out the logic board before buying a new power supply would disk warrior hardware test show the LB to be bad? I have more reason to believe it is the power supply because when i plugged a flash drive in it shutdown immediately. So I'm assuming as the flash drive draws power from the computer it drains the power supply...

Thanks for the response, any more input would be great
 
sounds like the cpu is overheating and thus getting a mandatory shutdown.. next time it does it, leave it off to cool for a bit and then see if it restarts normally... that would point to a overheating cpu.. also have you run the hardware check cd??

always handy when you have issues. :)

lol just saw that your temps are normal, what are they btw?? still run the hardware check cd though :)
 
Temps

Here i have uploaded the pic of the temps, i don't think thats the issue. It's running pretty cool. I just took the whole iMac apart just to check for imploded capacitors, and the ones on the power supply look fine... I basically pushed made sure the wires to the supply were tight. I didn't take the board out because it seemed like it would be a pain. I'm definitely inclined enough to do such things, i just don't want to have to resort to that yet. As of right now i'm on the iMac and it's running ok, but who knows it might shutdown again. I've read other forums where people replaced the power supply and fixed the issue. they described the same issues i'm having. When the computer shuts down it restarts right after. Maybe tightening the connections might have helped but who knows. It's tricky.. maybe it's the power supply but not a cap thats bad.
 

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Disk Warrior isn't even useful for telling you if you have hardware problems with your hard disk. It strictly focuses on repairing directory structures, and it's excellent at that.

Next time it's up, check through /var/log/system.log for the previous shutdown causes. Generally, anything zero or above is normal, and anything negative is probably not (though -60 is a battery dying, and -128 means it doesn't know).
 
Yeah for some reason i was under the impression that DiskWarrior had a test diagnostic similar to AHT. I do not have the Disk that came with my iMac so i cannot run AHT. Here i have uploaded a screen shot of my kernel.log as i searched shutdown. As you can see it shows a few -128 and then some 0. The weird thing is those 0's. I didn't shutdown normal any of those times. Those were all times last night i on the machine and it failed. It even seems like there were more times it's not even showing. I'm really hoping it's the power supply, last night i opened up the machine and checked the power supply. It looked fine and the connections look fine. So obviously i'm going to try the cheapest solution first. but the question i have is... Can a power supply that has no blown capacitors and looks fine still be failing? The shutdowns are so random, and then after having one sometimes the computer has a hard time restarting. It will just sit with a black screen as it tried to turn on, ill hear the fans huff for a second, and the disk drive start up as it usually does for second, then it will do that over and over until it eventually restarts. Or i don't even have to reset the SMC. If i just let it sit for like 10 minutes, it will start up normal. So i was just wondering if i should order the supply and try that first? As a side not when i type in my machines serial on the Apple site i still have Service and Repair coverage but I'm not sure what gets me. I can't imagine they'd fix it for free.
 

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If it's still under the three-year AppleCare, they'll fix it. If it were only shutting down, I'd go with the internal power/dc/inverter cable. Since you have a hard time starting it back up, it's more likely to be the power supply.

A shutdown code of 5 should be a normal shutdown or sleep, whereas on that machine, a 0 means power was disconnected. -128 shows up whenever it doesn't know, which happens whenever you boot to a different OS or device.

Make sure your power cable is secure, and then suspect power supply.
 
Alright, i really appreciate the help. I figured it might be the power supply, is there a shutdown code that shows logic board or smc failure? I'm assuming the combination of 0 and -128 shutdowns shows it's the power supply. So yesterday i bought a power supply and it should be in on Friday... Once i get it installed i can test the situation farther. Hopefully it will fix my issue.. It just seems with the codes and the fact the computer shutdown when more things draw power from it, it seems to me that could be the issue.

Thanks
 
Update...

So here the update, i got the power supply in today and i just got it installed in the iMac. Went to start it up and it did for a few seconds, but now it's even worse. Now i just starts restarting over and over... So is it possible it is either of the wires coming off the power supply. In other words they were just loose or something before, but not that i moved them they got even more loose? They power supply was said to be new, so there shouldn't be any issues. What do either of the wires do leaving the power supply? Im sure the larger set of them goes to the logic board somewhere, but what do the little set and the single wire do?
 
same thing has happened to me for the past week. It began to restart and after a few minutes, it would restart. Then after a bit, off and restart. It would be okay for a week then the restarting. Then it never came back on. I'd hear the Wally noise, HD spin, and the fans but no power to anything. Took it in Friday to the Apple store and hoping it's not the famed logic board. 5 months out of warrinty. :mad:
 
Sorry to hear that Al, these are the worst problems to diagnose. I'm thinking with mine it might be the DC cable... I'm not sure but it still seems to be a power issue, i'm still getting either 0 or -128. So could it be the DC cable going to the logic board, or could it even be a faulty power cable. I think i can rule out the power cable because my first light on the board stays on when it shuts down. If it were the power cable that light would go off right? So i think it might either be the DC cable or that other cable that looks like an inverter one. Any thoughts?
 
Hey, cp, I won't know anything until sometime this week. When I was leaving
The store a guy was bringing in his 27' iMac. When I am in there, I will show
Your post and ask about those shutdown numbers. I really hope the iPhone 5
will have a bigger screen, geeze.
 
That would be great i really appreciate it, my nearest Apple store is about an hour away... It may not seem like much, but i'm a college student, and it's tough to find time to do anything. It's killing me though because i'm on my 13" Macbook, and it's hard to do functional things on it. They iMac is way better, i miss it:apple:
 
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