It’s not very often a laptop comes in showing no signs of life, especially if it has a fully charged battery and a seemingly functional power source and power input. The first step would be to reset the Power Management Unit (PMU) per the instructions here. On PowerPC laptops, you’ll know the PMU is successfully reset because the indicator on the power plug will turn from amber to green and back to amber—or vice versa. On this particular iBook G4, the PMU reset procedure did not work. This most always indicates logic board failure, so I ordered one up and installed the next day.
The same behavior was observed after installing the replacement board, so I market it DOA and waited for its replacement to arrive the next day. No change in behavior. The likelihood of two DOA boards in a row is really low, so I took a mental step backwards and scrutinized my own diagnostics. I thought since the machine was still showing no signs of life it probably wasn’t the logic board after two replacements. If the PMU couldn’t be reset, the normal procedure for PMU reset involves use of the power button, and the machine couldn’t turn on, the logical component I forgot to isolate is the power button itself!
The power button is integrated into the top case of iBooks, so cannot be replaced individually. I snatched an extra top case and only plugged the power cable into the logic board. Whodathunkit…the iBook fired right up.