Power Mac G5 (June 2004) Firmware Update 5.1.8f7 (#4)

We continue to cover issues with sleep and excessive fan activity after installing the recent Power Mac G5 Firmware Update 5.1.8f7 (only for June 2004 Power Mac G5 models). The most common symptom of this issue is an unexpected, unresponsive blank screen accompanied by excessive fan noise.

It appears that in at least some cases, these issues are a variation of a previously reported problem with "thermal runaway" that causes another problem where some G5s fall asleep right after waking up.

In addition to "thermal runaway," some users have found their system logs riddled with hundreds of "forced thermal sleep" messages.

We're not sure why the G5 firmware 5.1.8f7 update is triggering a re-occurrence of these problems. And while users who haven't installed the recent firmware update are also experiencing the problem, there are a significant number of data indicating that there is at least some link between the firmware update and the kernel panic/sleep issues.

Operating environment temperature If you're experiencing a similar issue, you might want to experiment with the ambient temperature for the space in which your G5 is operating. Some users have found that "thermal runaway" instances -- as indicated in the Mac OS X log -- are less frequent when their G5s are operating in a cooler environment.

Known Issue? Several readers now report that Apple is, on a case-by-case basis, acknowledging the existence of this issue. In some cases, the company is replacing processors or other system components.

In addition, a few readers report that Apple technical support is asking readers to check their system logs (easily accessible via the "About this Mac" > "More Info" pane) for "thermal runaway" or "forced thermal sleep" messages.

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