iMac random shutdowns

[randy98mtu]

I've done some searching but didn't find any definitive answer on this. Does anyone know if there is a certain temperature that causes iMac's to shut down? I have been queuing up a number of movies in Handbrake and letting the iMac chomp away at them. For several months this was not an issue (this is a 2009 iMac 2.93 base model, no upgrades.) For the last week or two, I have come back to find the computer off a number of times. Every time it has done it it was while Handbrake had the processor pegged at 100% for a long time. The 3 highest temps are usually the power supply, the Northbridge and the CPU and the highest I have seen them is right around 70C. Last night I did some messing around with that fan control program and got the fans to run higher while Handbrake was running. I managed to keep all of the temps below 65C. I am going to leave it like this for a while and see if I have any more problems. I'm also going to try to cut back on the number I queue up at a time. I was setting up enough to keep it going for 12-14 hours. I don't actually think it was a time thing though as last night it shut down while my wife was using it and it was less than 2 hours after I started a batch.

Has anyone else had similar experiences? I see some people suggesting it could be caused by bad memory, but as mine only seems to happen with Handbrake at 100%, I'm thinking it's just heat.

Thanks for any thoughts. I'm hoping to avoid taking the computer in as it's just a hassle.

 

[geoffreak]

Seeing how you say that you make sure the temperatures remain low, it may be a faulty power supply that cannot keep up with the power needed under a heavy load.
I doubt the memory is at fault if it works under a normal load.

 

[indg]

run the apple hardware test cd that came with your imac to see if it's a memory issue. most likely it won't be your memory.

have you noticed any other graphical glitches, like odd lines, shapes, or pixels appearing over app windows or the desktop?

the random shutdown is usually caused by heat because the logic board/gpu progressively degrades over time due to internal heat. this is a design flaw. once you start experiencing the shutdowns, the damage is already done. the apple hardware test won't be able to detect this sort of problem.

the only workaround (not an actual fix) is to run the fans higher to stay below the "breaking point" temp before the system starts acting flaky or shutting down. on some imacs this is around 48C, on others it may be 56C. it varies, but in all cases the temp isn't abnormally high. cpu's and gpu's should be able to exceed 70C without failing.

this issue has been a serious problem with imacs since 2006 and 3 years later they still haven't figured out a way to prevent it.