Macintosh IIci

Batteries
Like many other Macs from this era, lithium clock batteries installed in this computer may be susceptible to leakage at the end of their lifespan. These batteries typically have a date code, so you can check their age. If they are more than a few years old, they should be replaced. Some brands are more susceptible to leakage than others - you are unlikely to encounter a Maxell battery that is still intact, but a Tadiran battery that came with the machine may still be fine.

If the battery does leak, this results in a brown residue and extreme corrosion on any nearby metal parts, including motherboard traces. Motherboards with battery damage are sometimes repairable, but it takes many hours or days of labor and almost always requires replacement of proprietary parts - on this board, usually the ROMs and the RTC - as well as repairing many traces.

Some machines with battery leakage have been known to avoid motherboard damage if the board was kept in storage sideways, usually resulting in a damaged disk drive instead. The screws will be rusted in place, so will need to be drilled out to remove the drive from its plastic carrier sled.

Capacitor Replacement
The surface mount aluminum-electrolytic capacitors on this machine are susceptible to leakage after many years. A majority of problems encountered on this machine will be caused by this capacitor leakage, which causes corrosion of traces and pads nearby. To prevent this, these can be replaced by a newly-made version of the same aluminum electrolytic capacitor, but these may have the same leakage issue in a few decades' time.

A common alternative is to instead replace them with tantalum capacitors, which will never have leakage issues. If you do this, it is vitally important that your replacement capacitors have a higher voltage rating than the original. If you do not, you will be risking a much more violent type of capacitor failure that may short traces and leave a burning hole in the board.

Apple motherboards from this era typically have a capacitor de-rating of about 75%, meaning that a capacitor on a 12v line will be rated at 16v, giving a bit of a buffer between the expected operational level and the capacitor's max rating. Tantalum capacitors are much more sensitive to their max rating and so should be de-rated much more - at least 50%, so 24v rating for a 12v line.

This board also has axial capacitors. These are not known to have leakage issues, and replacing them is currently not believed to be necessary, but also is not likely to cause harm.