iMac randomly goes into sleep mode. Help!

January 2, 2006 6:07 PM

My iMac randomly goes into sleep mode while I'm using it. It did it four times while I typed this question. WTF? It's an iMac 20" 1.8ghz.

I've installed no new software. It happens a couple times a day, then stops for a week, then starts again. All I'm doing is surfing the web and checking email. No one program seems to trigger it. Help!

posted by Manhasset to Computers & Internet (22 answers total)

Response by poster: I'm running OS X Tiger, with all the latest updates.
posted by Manhasset at 6:11 PM on January 2, 2006

Maybe you accidentally turned on the active corners. Try moving your mouse into each corner and see if it goes into sleep mode. If it does, go into your controls and turn it off.
posted by cyphill at 6:21 PM on January 2, 2006

did you check in preferences what it's set to? (System Preferences, then Energy Saver)
posted by amberglow at 6:23 PM on January 2, 2006

There's a setting calling "hot corners" or something like that, that causes the machine to automatically sleep if you put the mouse cursor into one of the four corners of the screen.

Google says the program is Expose.

You can turn it off.
posted by jellicle at 6:24 PM on January 2, 2006

Is this the notoriously bad Rev. A G5 iMac with the logic board with bad capactitors? Search any decent Mac news site or Apple discussion boards and you'll find endless discussion of this model.

Macintouch has a long reader discussion.

If so, the short answer is that you'll need to have either your logic board or your power supply (or both) replaced.

You might try resetting the PMU on the board first, but it may not help. Search Apple's support site for how to reset the PMU on this model. PMU = Power Management Unit. Replaced in later models with SMU (don't recall which this model has).
posted by mrbarrett.com at 6:29 PM on January 2, 2006

maybe it's tired.

did you check the apple forums? I assume it's under Applecare still, maye the Genius (hahaha) Bar could help.
posted by kcm at 6:30 PM on January 2, 2006

Response by poster: It's nothing obvious. The sleep is set to 20 minutes. It's not the hot corners thing as I have that disabled (and I just moved my mouse to each corner to confirm and nothing happened).

WCityMike, I doubt it. My friends are even less computer savvy than I am.

mrbarrett, I don't know if it is or not. It's not the kind that looks like the lamp. It's just over a year old.

I will search at macintouch but don't really know what I'm searching for.
posted by Manhasset at 6:55 PM on January 2, 2006

Response by poster: Okay, I just dl a program called Temperature Monitor as I have a suspicion that maybe it's overheating as nothing else seems to make sense. Someone on Macintouch also mentioned this. However, I don't know what the normal temperature is.

My cpu temp is hovering between 80 and 85 degrees C.
posted by Manhasset at 7:10 PM on January 2, 2006

that's waaaaaaaaaaaaay too high, 60C is about the limit I'd want to see a CPU at. I'm fairly sure you're going to have to have someone look at it. Do you have Applecare in effect still? It may be worth picking up if not, if possible. :)
posted by kcm at 7:11 PM on January 2, 2006

I have a Rev. A 17" iMac G5 1.8Ghz. Had to replace the logic board back in February (bad caps), and had to have the power supply replaced a couple of months ago.

Might want to take your system into an Apple Store and have it checked out...
posted by mrbill at 7:13 PM on January 2, 2006

Response by poster: Now it seems to have settled at around 68 degrees C.

Arrgh. I will call Apple, I guess. I thought it was no longer under Apple Care but it appears there's a week left.

I'm in the middle of a big job though and hate to be without the machine. What a pain.

Thank you for your answers.
posted by Manhasset at 7:23 PM on January 2, 2006

sometimes if it's a common problem you can get / pressure them to cover it even out of warranty. just FYI, and it takes luck and legwork more often than not.
posted by kcm at 7:30 PM on January 2, 2006

here's something about it--it says to get the logic board replaced.

i dl'ed Temp Monitor and my mini is running at 48c.
posted by amberglow at 7:41 PM on January 2, 2006

If it is a Rev. A iMac (when you bought it should settle that: about a year old is indeed a rev A., I think the rev Bs came out in early to mid 2005. They look exactly like the rev. As on the outside), then take it to the Apple store (or get Apple out to your house if you have AppleCare). It is quite probably bad capacitors, and you will need another logic board and power supply. My Rev. A iMac has already been into the Apple store for this.

Mine was also having sleep problems (it wouldn't sleep, it'd just shut down instead). IF it's a rev. A, that is quite likely your problem. The warranty has been extended to 2 years for that problem, even without AppleCare. See here.

Sleep related problems seem to be a very common symptom of this issue, even if the Apple support page I mentioned makes no specific mention of it. Indeed, it seems about 80-90% of the posters on Apple's iMac web board that are having sleep problems need new logic boards or power supplies or both.

And with all due respect to kcm, 80 to 85 C is NOT way too high. The G5 in the iMac is spec.'ed to run fine up to 85 C -- it will automatically throttle down if it gets hotter. While mine does not tend to idle there -- it stays 55-60 C now, high mid 70s when it's under load (of course it's winter now, and cooler in my house). A new PSU will cool it down a little, if that's the problem. Before I got mine fixed, mine was almost as hot as yours quite regularly. But it's within spec. I don't think it does a panic shut off if it gets too hot, because cutting the processor power in half will pretty quickly do the trick, but I don't know for sure.

The simple things you should do to isolate the hardware are: reset the PRAM and erase your energy saver preferences (I'm sorry, I don't remember where that file is right now). But I doubt it will help. There is a batch of bad capacitors almost in iMacs of your vintage that are almost guaranteed to cause problems.
posted by teece at 7:53 PM on January 2, 2006

I suppose the G5 does run hot, but that's pretty hot to be at constantly. For reference on the Intel side, my Athlon64 in a SFF case stays under 40C at load. 85C is way too hot, I sustain. :)
posted by kcm at 7:55 PM on January 2, 2006

Response by poster: teece, thanks for the extended answer. Your second link--I saw that before in August and brought my iMac in then. However, it wasn't a sleep issue for me, it was a scrambled video problem. It was in for 10 days and they fixed it.

What I find very strange is that page is dated October, 2005. However, I found the page initially through MacMentor, which linked to it in August, 2005. WTH?

It seems the unit was only at 85 when I first booted up. Since then, it's been hovering between 65 and 70.

The sleep problem happens over and over again (about every 10 - 30 seconds) until I reboot. Then it goes away for a week or two and returns for no reason I can discern. Started about a month ago.

I'll bring it in, I guess, but it's a pain (I don't have a car).

Also, your post makes it sound like Apple will come to my house if it's still under warranty. Is that true? I wasn't aware of that.
posted by Manhasset at 8:17 PM on January 2, 2006

die temps of 85C are probably fine. 40C is only about 112F, which seems pretty low to me. your temperature sensor might be borked. my athlonXP runs at about 55C at idle with ambient 21C, with a big ol zalman cooler on there.
posted by joeblough at 8:23 PM on January 2, 2006

My Athlon XP ran at 55-60C with a giant HSF on it, too, in a much larger case. That was the warmest x86 processor I've had in a personal machine. Regardless, you're correct, it only matters if it's in range for the CPU and thermistor placement across that model range.
posted by kcm at 8:24 PM on January 2, 2006

Manhasset: they won't come to your house if it's under warranty, but they will if you have AppleCare.

So you took this Mac in already? Hmm...? Maybe they replaced just the logic board, and not the PSU? Everything I've read indicates that the PSU is the primary culprit of the sleep problems. But it could always be something else, too.

kcm, while 85 C might seem hot, the engineers that built the G5 (and the folks that have to honor warranties), say that up to 85 C is OK for the G5. I trust 'em. It will only be at 85 C idling if your machine has a cooling problem, but low 80s is not at all out of the question if an iMac G5 is working hard. It's a tight case with a hot processor.

Sure, my Athlons run cooler -- but they have giant heat sinks and fans, sound like vacuum cleaners, are lower-power CPUs, and have much more airflow. The iMac G5 is basically a laptop that you use on a desk. It runs hot.

And for what it's worth, many folks on the PC hobbyist side vastly overcool their chips. It doesn't hurt, but it's not necessary. Many Athlons and Pentiums have similar acceptable heat ranges to the G5 -- anything below 75 C to 85 C is fine, depending on the chip.
posted by teece at 8:35 PM on January 2, 2006

Heat kills. It will spec out to such temperatures, but the lower the better for the longevity of the hardware - especially when you add in heated dust and gunk in contact with the surfaces. Plus, the increased ambient temperatures affect other nearby components most notably including the HDs. This is why I consider it to be a good thing to overcool. We're not disagreeing, you'll notice, I just never added the clause in my original comment that I had intended to about not knowing the thermal profile of the 970 and friends.
posted by kcm at 8:38 PM on January 2, 2006

If it occurs that frequently and a reboot fixes it for that long, then I doubt that it's a heat issue. That sounds like some kind of runaway process or something.

Can you correlate it with starting any particular program? Are their programs you only use about once or twice a week?
posted by willnot at 11:00 PM on January 2, 2006

Response by poster: No, I almost always use the same programs: safari, mail, photoshop, devonthink, transmit, vlc. They're almost always all open and I just switch between them. I see no correlation between the sleep and which app has focus or what I'm doing.

There was a time just before this happened that I was downloading a very large file from a very slow server so I turned off my sleep function and the computer was on 24/7 for about 10 days. After dl finished, I went back to sleep after 20 mins and then the probs started.
posted by Manhasset at 6:46 AM on January 3, 2006