Hi,
I'm having some troubles with the combo drive in my PB G4 (12'' 1. gen.), it will not read any pressed (original) CD's, they are just ejected after a moment of "chewing". CD-R, CD-RW, DVD and DVD-R discs work just fine.
I read on Apple's support forum that it may be related to the focus mechanism. Can any of you guys give any insight into this? and can I repair it?
Considering the amount of effort it will take just to get to the optical drive on your PowerBook G4, I'd recommend using this as an excuse to get yourself that superdrive you've been wanting. That being said, have you tried to boot from pressed cd's? Have you tried to replicate the issue with another user account. There are many alternatives to hardware issues, and many weird things can happen with the most bizarre of explanations. As an Apple Authorized portable tech, I start cringing when I see a 12". They're wonderful machines to use ( I used to have an 867 mhz 12.1" with combo drive like you do), but from a service standpoint, they are absolutely horrible. Hopefully, you have applecare on your PowerBook and can get service provided that way. Cracking open the 12" PB is tedious enough, but going inside an optical drive afterwards to test is even more so with no guaranteed reward.
So now I have tried: zapping PRAM, another user account, resetting PMU, and booting from a pressed CD (The hardware test CD that came with the computer) and nothing works.
And yes, I know that these machines are a pain to take apart, because I've changed the harddrive once. I suppose I should try a cleaning CD/DVD now and see if that helps. Otherwise I will have to live with it as I don't have the €€€'s to get another drive and I have no AppleCare.
A cleaning disc is probably going to be your best bet at this point since you've now isolated the issue to the optical drive. Unless you have a background in rebuilding optical drives, I wouldn't recommend cracking open your optical drive to fix it.
I have now used a cleaning-disc (actually a cleaning DVD) and now the combo drive reads pressed CD's again.
I don't know if it will last, though.