PowerBook 500's 
Powerbook 540c flaw..

If you have a 540c powerbook that freezes every 20 minutes there is something you can do. (I can't imagine living with this without doing something but maybe some of you have.) Early 540c models had a random freeze problem. It is caused by a flawed Motorola chip on the motherboard. Replacement boards are available. If you know you have this problem you can call Apple SOS at 1-800-767-2775. The fix is free.

More as they become more available..........stay tuned.