[Merkava_4]

PowerBook G4 - Titanium - 800MHz - DVI

The iFixit site says there's two fans: a primary and a secondary; which one comes on for max cooling when computer is really hot?

One of the fans that I assume runs the fastest will: spool up to speed and stop, spool up to speed and stop, etc.... The fan keeps repeating the struggle to reach full speed, but never quite does so because something causes it to stop each time.

Until I get these fans replaced, I'm trying to keep from doing things that are processor intensive.

[dowNNshift]

Because of the machines age, there very likely could be years of dust build up on the fans or a fuzz block up in the exhaust vent.

The fans rely on thermal sensors to tell the logic board how hot/cold the heat syncs are. If the thermal sensor(s) are not working correctly you'll get symptoms as you describe.

And lastly, remove your internal battery reset your PMU. When you remove the internal battery, does your TiBook forget the time? If so, the logic board backup battery is probably dead, this causes the PMU to forget and can lead to corrupted PRAM etc...

The bottom line is, you need to take it to a Service Provider so they can run Apple Service Diagnostic on it so that you can ensure the sensors are communicating properly with the logic board. Secondly, have a certified technician clean out the fan vents or replace them should you desire and replace the logic board battery if needed.

[Merkava_4]

Originally Posted by dowNNshift 

And lastly, remove your internal battery reset your PMU. When you remove the internal battery, does your TiBook forget the time? If so, the logic board backup battery is probably dead, this causes the PMU to forget and can lead to corrupted PRAM etc...

I have to remove the battery and cut the power sometimes when photobucket locks everything up. When I reinstall the battery and restart the computer, the clock still has the correct time. Those flash video adds over at photobucket are real hard on this old computer.

The exhaust vent appears to be clear from the outside, but there's no telling what's on the inside. Most of the time when I'm just surfing the web, the fans won't come on unless I run into flash videos.

Do you know which fan comes on when the computer is the hottest? Simple logic tells me it would be the secondary fan, but I'm not sure.

dowNNshift, thank you for your excellent explanations and help!

[Big Mac]

Are you running OS 9?

[AKcrab]

I would guess that both fans run all the time. I would download iStat menus and monitor the speed on each fan to see if you can figure out which one is misbehaving.

[Merkava_4]

Originally Posted by Big Mac 

Are you running OS 9?

10.3.9

Originally Posted by AKcrab 

I would guess that both fans run all the time.

No sir, they seldom run unless I run into flash video advertisements or load in a DVD.