[Guy Kuo]

Given the now documented propensity of some MacBooks to melt the insulation of a thermal sensor wire and develop random, intermittent shutdowns after a month or two of normal usage, I think it advisable for all MacBook owners to test their machines and expose any weakness while it is WITHIN warranty. A newly purchased MacBook probably should be thermal stress tested well before the 14 day replacement period expires.

Opening a terminal session and running yes in two windows maximizes CPU utilization and temperature. Several overnight runs or a 24 hour run without arranging extra ventilation should expose any machines that are physically prone to melting their thermal sensor wire insulation. The goal of the run is to heat the heatsink to as high a temperature as it will ever experience and hold it there for several hours. If the insulation holds, it should continue to do so. If it melts, the machine will start experiencing intermittent shutdowns during normal use.

A few days of normal usage after that session would give good peace of mind that the machine is less likely to fail later. Intentionally thermal testing early gives owners a better chance to have a fault prone machine repaired under warranty or replaced.

This would also be useful for newly repaired MacBooks prior to putting them back into critical usage.

[acoustix]

Maybe read all of this first....
The Apple Files » Testing your MacBook for Random Shut Downs

[Guy Kuo]

Originally Posted by acoustix

Maybe read all of this first....
The Apple Files � Testing your MacBook for Random Shut Downs

Right. A longer high temp run will more likely expose a insulation weakness than a few 15 minute runs. The RSD may not occur during the high temp run, but instead during the next few days.

[jamil5454]

Apple has a 1 year warranty on all machines, so don't worry about testing it before the 14-day return period. If it's opened, you'll have to pay a restocking fee anyway so getting it checked by Apple or calling 1-800-APL-CARE is your best bet for getting your machine replaced.

[badsey]

the test is not a bad idea. Also try running Memtest86 on your non-OEM memory especially if you went with a cheaper memory brand.

memtest86 clones:

http://www.macupdate.com/info.php/id/14004

http://www.memtestosx.org/

[SLiMeX]

I'm scared to try this, mine is a week 20 and nothing is wrong with it. It has also never been under enormus(sp?) stress like this test would give it...

[Guy Kuo]

You aren't forced to do the test, but here is my logic.

1. The early MacBooks have a heatsink/thermal sensor wire assembly that is prone to shorting if the insulation on the wire melts. Once the machine melts through the insulation during a high temperature episode, the machine can begin unpredictable, sudden shutdowns due to an intermittent short of the wire.

2. Once the insulation is compromised, the insulation doesnt heal itself.

3. Not all early MacBooks will develop this problem, but over time the risk of it appearing increases as the machine eventually will do some tasks which cause it to heat up. Each heating episode may further degrade the insulation.

4. The failure can occur after months of unremarkable usage. One may well use the machine without it happening until after the warranty expires.

5. Keeping a machine cooler by altering the firmware to make the fan come on sooner will slow the insulation degradation but does not actually make the wire insulation more resistant to heat. It only slows the onset if a machine is destined to have that failure. This is advantageous to Apple because the total number of failures within the warranty period should decrease and the failures spread out over a longer period of time.

6. Running Yes heats up the machine, but no more so than any other heavy CPU task like video compression or 3D rendering. The machine is designed to slow down the CPU and increase fan speed so running a heavy CPU usage application doesn't cause thermal runaway.

7. No all users will do enough heavy CPU tasks to thermally stress the wire insulation, but are likely to eventually do something that heats up the machine. It isn't reasonable to make users responsible for limiting their MacBook only to low CPU usage tasks.

8. An out of warranty repair is expensive.

9. A random shutdown event can cause the loss of hours of work even if one saves frequently. Imagine what happens if the machine is in the process of writing out a file and the sudden shutdown occurs. If it is overwriting the same file, both your original and you new work are destroyed. If it is during a file directory write, the directory structure could be munged. You usually get away without too much damage, but RSD events become more and more frequent once they begin and soon it becomes impossible to use a machine reliably.

10. I think it better to know a machine is prone to a failure before warranty coverage is over. Once the flaw is exposed a permanent fix can be done to prevent the problem and one can trust the machine. If a machine fails after a thermal load test, then it was probably destined to fail at a future date anyway. If it passes without incident, then you know your MacBook is less likely to fail in this manner.