Switching itself off

Latest update - the imac has been on for 3 hours this evening using it in target disk mode with fans at full throttle. I therefore conclude it is definitely an overheating problem. Can anyone suggest why in OS X my fans do not bank up when the temp increases and/or how I can provide extra cooling without the need for an external fan. Can the thermal grease be renewed on the CPU & heatsink?

THANKS

The fans run in full throttle in TDM because they are not being controlled by the temp sensors, since whatever is the host doesn't control the internal functioning of the G5. Your fans may not ramp up because they are not getting any instruction to do so. This would indicate a faulty temperature sensor. The thermal paste can certainly be renewed.

Miriam - you are a wealth of knowledge - thanks. I need to trouble shoot the fan ramping issue. I fitted a brand new sensor on Saturday but no difference in fan speed - i have this evening ordered an Apple sensor cable & I will try that also.

I wonder also if OS X has an effect - I have original 10.4 & cannot update due to shutdown issue & 512kb broadband constraints. Are there any instructions on how to renew thermal paste - I have the willingness & also a syringe of arctic Silver but the G5 cover & its fixings appear strange. I also read an article weeks ago and how to amend file to adjust speed of fans but I cannot find it anymore.

MANY THANKS

Do you have the iSight? [Internal pictures of iSight|http://www.kodawarisan.com/imacg5_isight/imacg501i.html]. It is quite difficult to disassemble, but if you have a Rev A or B it should be pretty straightforward.

[This article|http://forums.macrumors.com/showthread.php?t=259776] might be of help to you as well.

My iMac started turning itself off also and as far as I can tell, only when it hits the sleep mode. (even if I choose to sleep it). But it will stay running (for longer downloads) if I keep iTunes running. A work-around. And Doug posted a link that was supposedly solved but was only just a work-around also. We shouldn't have to work-around this problem. I'm afraid of the imminent "crash". Does apple address this issue anywhere? Seems like a motherboard/power supply issue.

Stephen

My Imac is non isight original 1.6GHz model.
I am a bit closer to resolving the problem. Imac works fine in target disk mode so fans on full must be overcoming heat problem.
I have disconnected HDD so no heat there & still imac powers off after 40 mins.
I have dismantled, removed logic boards & fans and hoovered out. Also replaced thermal paste (Arctic silver) on what I think is the CPU chip BUT after assembly imac still powers off after 40 mins use.
I noticed another chip (larger than cpu) with rough surface thermal pad on it - should I replace pad with arctic silver??? I am also considering replacing the bottom fan with a new one.
ALL help gratefully appreciated - THANKS

I'm afraid that I can't help with anything about the thermal pad, I simply don't know. At some point, you might consider taking it in and having a pro look at it.

Rich-
Did you get a solution. Many G5s were subject to "bad capacitors" problems and Apple, bless their excellent service, will replace logic boards and power supplys for free if your Serial Number falls within the range of "bad" macs.

I have an iMac (out of 150 which I maintain) which has been through 4 logic boards and three power supplys, and its still shutting down unexpectedly. New thought: perhaps the temp sensor on the hard drive bracket is telling the logic board that there is a massive heat problem.

Try it with that sensor cable unplugged.

Hopefully, this is for informative purposes only - as I will be taking mine in for that iMac G5 Repair Extension Program and hope to resolve this issue that way.

Model: Refurb 1.6GHz (pre-iSight) iMac G5
Early history: Fan ran out of control, shut down due to overheating: logic board replacement fixed (?) it. Later, OS patch also addressed it.
Later history: Even plugged into UPS, after power outage iMac would not restart until power cord was unplugged and reattached.
Current history: Upgraded to OS X 10.5.1, Energy Saver set to "Restart automatically after power failure". After clean install of 10.5, it shuts down (and restarts) several times a day, but never while I was working on it - 1:45am, 2:15am, and 3:20am this morning alone before I turned off the auto restart. This was definitely not happening before 10.5 was installed. Contributing factor may be lack of that OS patch due to doing a clean install.
Also, the Sys log in Console shows "AppleSMU -- shutdown cause = -110" during each of those three shutdowns mentioned.
Resolution: Taking it in for iMac G5 Repair Extension Program - just makes it in under the 3 year deadline. Will post results. I'll be using the program mentioned here though: http://www.apple.com/support/imac/repairextensionprogram/

I took my iMac in to the local Apple Store and presented my case. The guy behind the Genius Bar was happy to see the Sys Log I printed from Console identifying the shutdowns. He said it qualified for the extended warranty program, but they had to order the parts and it could take 4-7 days to repair. *25 hours* later I got a call to come pick up my iMac, complete with a new logic board and power supply.
Since I've had it home, there have been no issues whatsoever. The fan got a little loud during a prolonged upgrade install, but that was it. Happy ending to the story.

Just thought I'd share my experience with this issue. One thing to note: I run a webserver on my iMac, so it's always on 24/7.

I started having the sudden shutdown problem a couple years ago. I have AppleCare, so I took it in and they replaced the power supply.

About a year later it started shutting down intermittently again. By that time the Repair Extension program had been announced, so I was able to get it repaired again--this time the logic board and power supply were replaced.

Now it's another year later and it's happening again. The other night it shutdown spontaneously 3-4 times within two hours (around 4am). Luckily, I'm still within the 3 year time frame of the repair program, so they are replacing the logic board and power supply again.

I also had the error message of "AppleSMU -- shutdown cause = -110" in my system log.

One thing I'd like to say is that the customer support at the Apple store has always been courteous and helpful. Most people just post when they have a bad experience with customer service, so I'll try to balance the scales here by noting my positive experience.

Anyway, I don't know if running my iMac 24/7 is exasperating the problem or if the G5 is simply flawed in design and can't handle the heat. Regardless, I'm expecting this fix to only last another year or so, at which point my repair coverage will be expired and I'll have to start looking for a replacement. I'll probably switch to a more flexible setup with a separate CPU and monitor.