I’ve had many problems with my recent 27″ iMac. First was a video problem, that was corrected with the 10.7.1 update, then came a problem with a burning smell coming from the computer. This smell only arises when I really push the iMac – converting videos with Handbrake, for example – and led to my contacting AppleCare for a solution. They had a repair center take the iMac, do tests, and, the first time, change the logic board, as the technician spotted a piece of scotch tape touching the processor.
After this repair, I got the iMac back and was happy. Until I converted another video; the smell occurred again. Back for repair, tests, yet nothing was found. So it was sent back to me.
All this time, I’ve been in touch with a level-2 AppleCare technician who has been very helpful, and who has tried to find a solution. But we’ve come across something extremely odd, and can’t figure out what could be the cause. Here’s the deal.
The burning is clearly caused by excessive temperatures. The iMac has a number of heat sensors, and I’ve recorded the temperatures when converting videos, to see how high they go. I won’t list all the temperatures, but rather the one that is the highest, the secondary heatsink. This is the inside of the back of the iMac – the aluminum back is a massive heatsink. In my tests, this sensor went up to 89 C. In the tests at the repair center, it didn’t exceed 66 C. And yesterday, I tested the same process – converting a video for an hour – in different rooms of my house.
First, in my office, it reached 89 C. Then I tried in my wife’s office, where it only hit 73 C. (That room was 2 degrees cooler, but those 2 degrees are not enough to make that much difference.) I then tested it in the living room, on the ground floor, where the temperature was the same as in my wife’s office. It hit 89 C.
So, the conundrum: what is causing this difference in temperature from one room of our house to another? I’ve ruled out voltage (I’ve tested in all rooms, during the tests, and it’s around 238 V.) It’s not peripherals, as the tests were done with nothing connected, only a wireless keyboard and Magic Touchpad. All the tests were done with the same power cable (and I’ve tried two different ones), with absolutely no variables other than the socket they were connected to. (All connected directly to the wall, not to power strips or UPSs.)
If anyone has an idea, I’d be grateful if you could post a comment. Thanks.
Update: I’ve found some very odd behavior on this iMac. The AppleCare technician asked my to do some tests using Snow Leopard. While I wasn’t able to get everything exactly the same (I booted off of an external USB drive), the discrepancies between Lion and Snow Leopard were more than surprising.
Using Handbrake for my tests, converting a .dvdmedia file, and using the same file both with Snow Leopard, then, later, with Lion, I found the following:
- Temperatures were much lower with Snow Leopard than Lion. After an hour or so, the secondary heatsink was only 47, compared to as much as 89 C with Lion. There was a difference in temperature in my office; it was a few degrees cooler than during my tests the other day, but that is not where the difference lies.
- Using the same file conversion with Handbrake, Snow Leopard draws between 16 and 17 W and between 16 and 17 A. With Lion, the same file, there was 36 W and 33 A being drawn.
- With Snow Leopard, after an hour, Handbrake was converting the file at about 29 FPS. With Lion, Handbrake converts the file at 46 FPS. (Other files in my tests the other day were over 60 FPS, and I didn’t let the conversion run very long with Lion this morning; at times, the FPS rate increases during a conversion.)
Now, there are a few very small differences in my tests that would skew the results just slightly. My Lion tests today were with my standard account, so there were some background processes running. This would limit Handbrake’s access to the processors by a few percent, which could explain why I only got 46 FPS under Lion today compared to over 60 FPS the other day with a virgin account. But in all cases, the processor was being used to the max; all four cores were spiking, with total CPU usage around 390% or more at all times.
So, what does this mean? For some reason, Lion is using my processors much more; not only are they drawing twice as much power, in both watts and amps, but they are working harder (the FPS difference with Handbrake). I have an i5 processor which does not support hyperthreading, so that’s not how it’s working harder. It’s almost as if the iMac is overclocked with Lion. My thought is that this Mac was designed when Snow Leopard was available, so the temperatures and fan speeds are designed for that OS. But if Lion is doing more with the same processors, then the temperatures are naturally higher. It’s worth noting that there are a number of threads on Apple’s forums where people are experiencing higher temperatures with Lion than with Snow Leopard. I am curious to know what is going on; the temperatures I get when doing pretty much nothing (writing, web browsing, etc.) on Lion are higher than Snow Leopard temperatures when I’m maxing out the processors.
This does not explain my differences in temperature from one room to another; one friend suggested a grounding issue, which I’ll look into soon. But this difference in both temperature and performance is certainly surprising.
Posted: 9/30/2011 by kirk | Filed under: Apple & Mac OS X Tags: iMac, Mac OS X, troubleshooting | 12 Comments »
See an expanded version of this article on TidBITS.
I’ve generally been fortunate when upgrading to new versions of OS X, but this time I’ve been hit with a nasty bug, that’s already caused me to lose some work. I have a new 27″ iMac, purchased in early June. This computer worked fine under Snow Leopard, but once I installed Lion, I started seeing random freezes when viewing videos. The videos could be any kind – Flash, H-264 or QuickTime – and the freezes are mean: the entire screen locks up, except for the cursor, and, while sound continues if I have iTunes playing in the background, I can’t do anything else but a hard restart. Sometimes it simply freezes, and other times I get displays like this (this is a screen shot I took of a QuickTime Player window; my iMac froze when I tried to close the window):
When this happens, the following messages are written to kernel.log:
7/23/11 12:02:40.000 PM kernel: ** GPU Debug Info Start **
7/23/11 12:02:40.000 PM kernel: 0x00006740
7/23/11 12:02:40.000 PM kernel: 0x0000008f
7/23/11 12:02:40.000 PM kernel: 0x00000001
7/23/11 12:02:40.000 PM kernel: 0x00000018
7/23/11 12:02:40.000 PM kernel: 0x0000a880
[and so on for a few hundred lines]
There’s a pretty long thread on Apple’s forums of people confirming that they, too, have this problem, and there are other threads discussing it as well. I called AppleCare on Saturday, and the technician was not aware of this problem. I told him I knew he wouldn’t have a solution, but wanted to make sure that the information got to Apple’s support technicians so it would go up the chain.
For now, I avoid watching any kind of video on my iMac. My MacBook Air has no problem, so I use that. But this is a disturbing problem, clearly related to Lion, which will hopefully be fixed in the first Lion update, which is likely to be released this week.
Update: I got a call back from an Apple technician this afternoon, asking for more information, logs, system profiles, etc. So I can confirm that Apple is indeed looking into this. It was relatively easy to reproduce the problem while on the phone with the technician, alas.
Update 2: The Apple technician has had me try a number of things to eliminate various possibilities – removing certain caches, etc. So far, none of them has led to a solution. The Apple forum thread is getting longer…
Update 3: The Apple technician asked me to test my Mac without the third-party RAM I had added. It froze pretty quickly. But while I was at it, I tried removing the original RAM, and was unable to make it freeze, no matter what kind of videos I viewed, even with many at a time. This may therefore be the culprit, even though a number of people on the Apple forum tested their RAM and found no problems with it.
Update 4: I just had a freeze, so it’s not the RAM. Too bad; that would have been an easy solution.
Update 5: I’ve been working with an Apple engineer for the past week, and he had me try everything suggested in this very long therad. He also asked me to do a clean install on a different disk, which I did yesterday. I was unable to reproduce the problem, despite running lots of videos, sleeping often, etc. This doesn’t mean it won’t happen, but I was able to easily reproduce it on my main boot partition.
There are certainly many variables – the clean install had no third-party sofware installed. But given the number of people posting here, I doubt that there’s any third-party software responsible. (Also, the Apple engineer has seen my crash logs, and hasn’t suggested that any specific software could be responsible.) So I’m a bit flummoxed by this latest development…
Update 6: I was able to get a freeze on my clean install. So that rules out any issues specific to my installation, third-party software, etc.
The story so far: Let me summarize the problem here, and discuss the many solutions proposed on the very, very long Apple forum thread. Viewing videos of any kind cause freezes. This doesn’t happen every time one views a video, and only happens after an iMac has been put to sleep at least once, or, in some cases, multiple times. These videos can be Flash, H-264, or QuickTime formats, and viewing may occur in Safari, Firefox, QuickTime Player, iTunes or any other program.
Doing the usual troubleshooting steps, such as resetting the PRAM or SMC does nothing. Doing a clean installation of Lion, with no third-party software installed, does not solve the problem. Deleting and/or reinstalling Flash has no effect on it. RAM or other hardware has no effect, though it may turn out that this is a hardware problem with video cards. (This seems unlikely, because many people with this problem, including myself, had their iMacs with Snow Leopard, and did not have freezes.) In short, none of the “solutions” offered on the Apple forums resolve the issue, as you can see in the trials I carried out in my various updates above.
For now, all we can do is wait on Apple. I’m willing to give Apple a bye on this for now, but this is starting to become a long time since the discovery of this issue. I can understand the anger of some users, and I’m a bit surprised that Apple didn’t discover this. However, it’s entirely possible that they didn’t have the new iMacs any earlier than users did for testing. (Which is, of course, reprehensible.) While some posters in the Apple forum thread mention similar problems with MacBook Pros, it is not the same problem; iMacs freeze; MacBook Pros seem to have kernel panics, and it seems to be a much more isolated problem.
In any case, I’ll continue updating this post as I get more information.
Update 7: I got some interesting information from someone who knows a lot about graphics cards and drivers. One of the most interesting things he said was that the number of background processes running may have an effect on this issue. This is interesting, because when I tried reproducing it on a clean installation, with no third-party software installed, it took quite some time to induce a freeze. On my normal installation, it’s much easier to reproduce the problem, and I do have a lot of third-party software installed that runs background processes. Nevertheless, this does not offer a solution to the problem, and Apple has still not come forth with anything. This is starting to become a bit long. Sigh.
Update 8: On August 16, Apple released Mac OS X 10.7.1, a small update which claims to “Address an issue that may cause the system to become unresponsive when playing a video in Safari.” It’s not clear whether this resolves the current issue. In my initial tests, I was unable to get my iMac to freeze, though I was seeing some artifacts when starting to play videos using QuickLook. It will take a while to be certain whether or not this resolves the issue. If anyone reading this has applied the update and is still having the problem, please post a comment.
Posted: 8/17/2011 by kirk | Filed under: Apple & Mac OS X Tags: Apple, iMac, troubleshooting | 60 Comments »
About two years ago, I downgraded from a Mac Pro to a Mac mini. I like the Mac mini a lot, but there are some limits, notably in hard disk space. I have a very large music collection, as regular readers have probably noticed, and I have an external hard disk to store it.
But the new iMacs come with an option to use a 2 TB hard disk. My media disk is 1.5 TB (and it’s not full), so if I had a Mac with a 2 TB hard disk, I could not only put all of my “normal” files but also store my music collection on it, eliminating the need for an external hard disk. (I would still use another external hard disk for backups.)
Furthermore, the ability to include an SSD as a boot disk would be a big plus. I have a 13″ MacBook Air and am delighted with the speed of the SSD. (In my Mac mini, I have a Seagate Momentus XT hybrid drive which is faster than a normal drive, but not quite as fast as an SSD.
The only thing is this: late last year, I bought a new Apple 27″ Cinema Display, and if I want to buy an iMac, I have to sell both the Mac mini and the display. Not easy to do, here in the sticks where I live (and I don’t want to have to deal with shipping stuff like this).
In any case, Apple has a 4-6 week delay for iMacs with the SSD, so I have time to try and find a buyer. Not that I’m a speed demon, but I’d welcome a faster Mac than my mini, and especially the increased hard disk space, the SSD, and the ability to have 8 GB RAM instead of my current 4 GB. And that Thunderbolt thing sounds interesting too…
Is anyone else tempted by the new iMac?
Posted: 5/6/2011 by kirk | Filed under: Apple & Mac OS X Tags: Apple, iMac | 15 Comments »