From what I can gather, the well-known faulty GPU is more an iBook G3 issue (700/800/900Mhz models); with the faulty vreg chip being more a problem with iBook G4s. However, GPU issues also occur in later G4 models, but not as frequently as their G3 counterparts. Either way, both issues are caused by a poorly-designed, flexing motherboard causing delamination of components. The quick fix for both is to place firm pressure on the faulty chips in question to get the iBook to power on for a little while. However, this usually doesn't last long until more aggressive repair is required.
My most recent, and unsuccessful, repair on an iBook G4 1.07Ghz involved scraping back the traces and resoldering the vreg chip in question. The previous owned used rubber stoppers and pieces of a credit card to place pressure on the vreg chip - obviously it didn't "take" after a while, so he/she kept adding more spacers - about eight all up! When I received it, I was able to get it to fire up and work well with the vreg resolder, but it would then fail after about 30 minutes of use. Several resoldering attempts later, I gave up - clearly the previous user had flexed the board so much, it put stress on the rest of the board, making it become more and more unreliable over time. But let's hope you have luck - the other two iBook G4s before this one I was able to fix successfully.
Regarding your 12" Powerbook, I doubt a similar issue is occuring here, but you could always gently flex the board and/or place pressure on various components in an attempt to get it to boot. Might do very little, but you're little to lose!
JB
My most recent, and unsuccessful, repair on an iBook G4 1.07Ghz involved scraping back the traces and resoldering the vreg chip in question. The previous owned used rubber stoppers and pieces of a credit card to place pressure on the vreg chip - obviously it didn't "take" after a while, so he/she kept adding more spacers - about eight all up! When I received it, I was able to get it to fire up and work well with the vreg resolder, but it would then fail after about 30 minutes of use. Several resoldering attempts later, I gave up - clearly the previous user had flexed the board so much, it put stress on the rest of the board, making it become more and more unreliable over time. But let's hope you have luck - the other two iBook G4s before this one I was able to fix successfully.
Regarding your 12" Powerbook, I doubt a similar issue is occuring here, but you could always gently flex the board and/or place pressure on various components in an attempt to get it to boot. Might do very little, but you're little to lose!
JB