In this past week, I have come across three Powerbooks that constantly BOOT into sleep mode. Regardless of OS install, these units immediately go to sleep once the Login Screen comes up or the Finder loads. In each of these cases, I found that a Thermister (temperature sensor), was diagnosed as bad by the Service Diagnostic. The only solution for this was to replace the entire top case in the Powerbooks. Of the three customers, only one was under Warranty. It’s hard to
believe that such a small sensor, integrated into a pricey part, makes the computer unusable, but that’s what happens.
As a FYI into the pathway of the failure, the thermisters were reporting falsely that the operating temperatures were out of range, too hot. There is a fail safe built into the OS, when it senses abnormally high temperatures. Basically, when the onboard monitors sense that a component is running too warm, the machine is forced to either shut down or sleep to keep the Machine from ‘overheating’ and burning up or burning out a component.