Chosen Solution
This iBook has been working fine for years, and began to behave strangely quite suddenly: the screen flashed and audio played. At restart worked at first, then it crashed. We were able to run in FireWire mode to back up some files. A subsequent attempt to startup from DVD failed (and the disk will not eject). Now it will not boot at all: no chime, no screen display, no FireWire disk mounting. A fan starts when power button is pushed, and stops when pwr btn is held down for a few seconds. Otherwise, nothing. Tried keystrokes for PMU reset, no help. The battery is good (4 lights) and AC adapter seems ok. Could this be a DC board problem, or is logic board failure more likely? What to test first?
Are you sure you reset the PMU correctly? It’s not the first thing I would try. I would first reset NVRAM/PRAM Then I would try resetting the PMU Apple TN on Resetting the PMU.
I agree that this is most likely logic board failure, but just one note – G4s often get shorted out by loose screws on the underside of the board, and produce the “fan on high” issue you’re experiencing. You might want to remove the lower shielding, and see if any screws underneath fall out, or if any of the screws connecting the board to the frame are visibly loose. Then, try powering on with the lower shielding removed.
