PowerBook G4 power issues

Try: Resetting PowerBook and iBook Power Management Unit (PMU)

Sounds like a thermal protection shutdown if the PMU reset doesn't change anything. There are sensors that shut off the computer to save it from frying if temps approach dangerous levels. You should not hear the fans at their normal idle speed of about 2000 rpm except in a very quiet setting.

If they start right away, that sounds like a failed temp sensor someplace. To avoid overheating due to a bad sensor reading, the system is designed to be smart enough to switch to a "safe" condition that runs the fans full speed (about 6000 rpm) if a sensor fails.

Some of those sensors are on the logic board. Could be a real problem

is there any way to run a diagnostic test to see which of the sensors have gone bad?

Only if you have the original disks that came with the computer. One will have Apple Hardware Test, which throws a code if it finds a failed component. Codes are rather arcane but many of us here can "mostly" translate them. A code with "SNS" is a bad sensor; other info in the error code is supposed to point to which sensor. A code of MOT means a bad motor, usually a fan.

Those PowerBooks have two fans. I recall now that, should one fan fail, the system immediately triggers the other to full speed to make up for the reduced airflow. That would be the best outcome as replacing fans, although not your average DIY project, is hugely less cost and hassle than replacing a logic board.

The typical logic board problem with 2005 15-inch PBG4s was that one RAM slot would simply stop working. Apple replaced a lot of logic boards , so much that they ran out of new boards and had to start refurbishing defective ones. That means two things you don't want to hear:

• so many bad boards were pulled and replaced that there are painfully few known-good boards floating about on the used/pulled market
• if you do find one, the chances are high it is one of the defective ones that some unscrupulous type decided to sell instead of destroy

Apple put out downloadable versions of AHT (each is model and sub-model specific) but the one for PowerBook G4s was a bad file and never worked. Without original disks, you are sorta messed up.

You could try other specialists whose business centers on repair restore with

parts and services; that would be someone who could repair the computer

after a test of the unit altogether, and also test it after a repair to be sure it is

in working order; then they offer a limited guaranty on their work & the parts.

Several are out there, not sure about powermedic except they offer a limited

guaranty on the parts. However that may be a lot of work to find out if the

part works OK once you install it into your computer; or find other issues after

taking the computer apart & putting it back together again. Other stuff fails.

Sometimes a repaired working guaranteed portable Mac is a fair bet, however

if the kit is missing important (original discs, accessories now rare, etc) you

may have a harder time finding those. Video adapters are also hard to get.

I'd check around to find if other companies such as powermax, welovemacs,

wegenermedia, macsales (owc), and others with a long standing reputation

can offer an affordable service, a partial, or a complete restore. I'd had a fair

experience years ago w/ wegenermedia at great distance, a dualUSB iBook.

So I'd probably try them again if I get my act together and want to commit

some funds to one of my portables that need some work I don't want to do.

You could look (if you haven't) into the powerbookmedic site, and then ask

them directly about that logic board and how they test them. A tested-good

part by itself sounds OK but once you have the computer taken down to

get that far, a weak original logic board may be suspect on durability. If you

are very good at tedious and detailed projects, $50 is inexpensive... That

is just the cost of admission, to what may be hours of unsatisfactory effort!

Have you studied the online youtube DIY repair videos, and DIY sites to

repair stuff, to see if you are up to all the other details involved? Most of

it looks fairly daunting to me, since my concerns would be what can go

wrong in the process to extract the logic board. re: Other parts damage.

Good luck in that matter & happy computing! 🙂