Macintosh 512K

Resources

Wiki
everymac.com
How to Generate Floppy Disks for Old Macintosh Computers
Service Source
Mac Startup Keys
Sad Mac Error Codes
Classic Mac Tech Info

Internals

Motherboard

Analog and Power Supply Board

Similarly to Macintosh Plus, the board uses a rare 4.5V PX-21 battery. The computer will perfectly boot and work without the battery, but the date and time settings will not be preserved.

List of capacitors for recapping the board:

Boards originally setup for 120V can’t be easily modified to accept 230V. The results of attaching a 120V board to 230V do not always have to be lethal to the board though. I messed up once and did it – the 100uF/250V capacitor blew up like a cracker, but the fuse broke the circuit and nothing else was damaged.

Floppy Disk Drive

Sony OA-D34V floppy drive is a single side 3.5″ 400K drive. It produces a fantastic sound when working. In later versions of this Mac, called 512Ke an 800K drive was installed. OA-D34V was the oldest original drive installed in 512K and there were also upgraded versions called OA-D34V-22, which needed the Mac’s ROM to be in revision B.

The drive loading mechanism gets stuck with time due to the original lubricants getting thick. You can restore it using Isopropanol (IPA) in spray, ear buds and a little of gentle force.

With a working loading mechanism, the drive is also likely to not read disks well after a prolonged time of being not used. When drive can’t read the disks (or the disks are bad), Mac will report Sad Mac icon with 0F0064 code when trying to load the system.

One of the likely causes may be the head stepper motor – it won’t get stuck completely, but will become hard to move and loose calibration of the head position. Spraying the motor with IPA and carefully moving the head out of its original position and starting the Mac will force the motor to seek the zero track and eventually it can get into good shape, having repeated it several times. It worked well for the two drives that I have.