G3 & G4 Logic Board Fix (Please note I hardly ever to this method anymore)
I used to fix alot of G3 ibooks with this method but to be honest only lasts for
a few months until you have to repeat the whole process again.
(Updated 24th May 2008)

Instructions:
1. Remove your ibook's lower heat shield by following ifixit's instructions.
2. You should now be looking at the bottom side of the logic board. See pics below of two ibooks
with the problem chip outlined and blown up.

UPDATE: Please see the above image of an ibook 800Mhz, slightly different logic board layout.
Problem chip highlighted in light blue square.

3. Now you will need to place a shim between the chip and the heat shield/case. Here's the little sticky rubber feet I used and what I'd recommend. I also used a rolled up piece of copper on one ibook, but that was just what I had laying around during my aforementioned fit of frustration. Really, anything seems to work.

It does not seem to take too much pressure on the chip to get the computer working. I tried to keep my shim as short as possible. You may need to experiment to find what works best for your laptop, but the shim must be tall enough to reach the plastic case! Otherwise not enough pressure will be put upon the chip.

UPDATE: It seems that the more pressure, the better. However, be very careful not to damage your logic board by using too large a shim! I suggest trying the smallest shim possible and seeing if it works. If you have problems increase the size of the shim slightly and try again. Keep going until you find the best fit.

4. Here are pics from both my fixes. One with a piece of rolled up copper (from a cosmetics tube) and the other with a rubber foot. You may have to re-route the power cable around/over your shim a bit. I decided to leave the copper shim in place (instead of replacing it with a rubber one) just to see if it works better than the rubber one. Obviously the rubber foot is bigger than it needs to be. Feel free to cut it down to a more proper size.

5. Re-assemble your ibook. The case may be slightly deformed as the shim should be pushing against it. Try not to use a shim that is too large, though, as it may put too much pressure on the logic board causing further problems.

6. Bingo all working again!

Please note: while this fix has worked 5 times for myself on different ibook G4s, I take no responsibility for it working on your machine however. Please note by opening up your ibook you void any warranty you may have on it and also causing even more damage in the process.

Credit goes to http://www.coreyarnold.org/ibook where I found this method of fixing
the G3 & G4 logic boards. If you want to try it yourself just take it easy and take your time,
otherwise contact me. This fix is also very depedant on how easy it is to open up you machine,
regarding screws etc as some can be a nitemare to unscrew.

* Due to the nature of the G3 & G4 logic board problems, logic board fixes can not be guaranteed.