My PowerBook has gone nuts it seems. I got it a week ago and have replaced the upper and lower case, and heatsink + fan assembly. So that's two top cases, and two fans. Neither solved the problem. I think its software related, or something is wrong. When I scroll, or put the computer under any type of load, the right fan will operate properly. As soon as the computer doesn't see any load, the fan fails to spin even though it should be at a low RPM. It is basically cutting out for some reason. I've attached a video so you can see what I'm talking about. Click it below and turn up your audio volume a little so you can hear the little fan trying to spin up in conjunction with the scrolling. Running 10.5.8 Leopard. ---------- It looks like the "Power Supply" temperature sensor (Sensor 3 in the photo) may be causing the problem. It jumps around all over the place whenever I move the my finger around on the trackpad. Is this sensor on the power board on the left of the laptop where the power adapter plugs in?