Firstly, be careful when taking the machine apart. When you spread the two halves of the bottom case, don't lift it to far. From the rear use a plastic tool to unplug the grey cable (Interconnect Cable) from the Daughter-Card. Lift each end of the black connector where it "overhangs" at each side of the flat cable. This cable is very delicate as each wire is single stranded and can break easily (inside the grey plastic covering the cable).
Also, be extremely careful with the case plastics ESPECIALLY the display housing. There are small brass machined nuts molded into the plastics and these often break leaving you with a virtually unusable machine. If they are intact, there will usually be hairline cracks in the plastic surrounding the brass nut inserts. I used to apply
Araldite around these, taking care to observe clearance for other components and ensuring not to get glue into the threads - a disaster if you do. Less is more when doing these. The same applies to the screws that secure the motherboard to the bottom case and the floppy & hard drive frame mountings too.
Minimum would be, Motherboard, Daughter Card & Cousin Card which plugs into the Daughter Card, IIRC. You'll need headphones plugged into the motherboard to hear it power up since the speaker is in the top case and is one of the things connected via the grey cable I mentioned above.
The circuit board that the grey cable connects to in the top case also houses a rechargeable battery, which may require replacement. It's a 3v 30mAh rechargeable Lithium battery. Hard to get in such a thin form-factor.
Check that the voltage of your AC Adapter is 7.7 volts when not plugged into the PowerBook and also when it IS plugged into the PowerBook.
There is also a fuse soldered to the motherboard next to the battery contacts. It's a white rectangular box marked as "F1" next to it. It is a
LittelFuse 5Amp 0459 Fast Blow series fuse.
If you smell anything burning, unplug the power and quickly see if any component is particularly hot.
A useful resource would be found by Googling : "powerbook_165c.180c.pdf"