Macintosh 128K (JG 2)

This computer belongs to a customer who dropped it off in parts. The case and analogue board belonged to an original 128K, but it was upgraded to a Plus at some point. The owner wants to convert it back using a replacement 128K board and 400K floppy drive.

Work done so far

Inspect boards
Cleaning battery corrosion
Repaired traces
Replaced bad capacitors
800K floppy drive cleaned and lubricated

Initial inspection

Here are some pictures of the computer while opening it up:

Here is the logic board, it seems to be in good condition. It's unknown what kind of work was done, but it looks like all the memory modules were socketed at some point.

Cleaning and repairing the corrosion

Here are a few pictures after some initial clean up using vinegar to naturalize the battery electrolyte:

The flyback was initially whining quite badly before adjusting the cut-off potentiometer. I checked the flyback itself and although it does appear quite discoloured, it's now working correctly:

Here it is on the first boot attempt, it wasn't able to boot off of the floppy.

The flyback was still quite noisy, except when touching the analogue board, which would indicate cracked solder joints. After touching up all the bad looking and likely cracked joints, the flyback is no longer whining.

Here is the completed analogue board, quite a few traces had to be repaired and were re-covered with solder mask.

Logic board

The logic board that came with this computer was swapped with this computer, to return it to a an original 128K. The text below is about the board which ended up in this computer.

This board had been upgraded to 512KB of ram in the past by swapping the ram ICs and making some minor modifications, it's impossible to say when, but it looks to be quite old:

Because I couldn't get the 400K drive meant for this machine to work, I had to upgrade the BIOS using a ROM chip from a donor machine to support the 800K drive. Below is an image of the completed board:

800K floppy drive

The original 400K drive was used to replace the faulty one on this computer and instead it was decided to refurbish the 800K drive that this computer came with instead.

The drive was quite dirty, but in fair condition:

The eject mechanism on these 800K floppy drives fail quite frequently, it's caused by a specific gear, made of a different type of plastic which becomes soft over time.

I replaced it with a gear from a 1.44mb donor drive whose's head was faulty. The gears in these drives don't suffer from the same problem.