Macintosh Color Classic

Most likely the front of the case was exposed to some kind of liquid, I found this white dirt in several places close by:

This also likely caused some of this corrosion:

I cleaned up the worst on the analogue board RF shield:

Finally, here is a shot of the computer booted up:

Analog board

Many of the electrolytic capacitors on the analog board were showing high ESR values, even though they didn't show any signs of physical leaking.

Unfortunately, I didn't take any before pictures, but here is the final result of the board after replacing them:

Logic board

The electrolytic capacitors on the logic board had been leaking quite severely, damaging a few traces and building-up a lot of electrolyte goop between IC pins:

After replacing all the electrolytic capacitors with tantalum versions, the board refused to start, which lead to a long troubleshooting session:

These computers have a soft power feature using the keyboard, there is a power button on the back, but the computer won't start unless you press the power button on the keyboard.

I ended up double and triple checking all the repairs I had performed, including removing all the capacitors and installing temporary ones to check for damaged traces I might have missed, but nothing worked. In the end, I started soldering wires directly to the ICs to probe them using the oscilloscope, since it's not possible to run the logic board outside the chassis.

After a while I found that the clock signal for the keyboard controller was missing, and it turned out that the clock crystal had failed. Once I installed a replacement crystal, I was able to start the computer normally.

At this point, I could go ahead and replace all the temporary capacitors with another batch of tantalums I had ordered again. Here is the finished board:

Floppy drive

The floppy drive was fairly clean, but the grease was fully dry. I disassembled the drive to fully clean and lubricate it: