Restoring an AT 286

I found a Commodore PC 30-III (286 @ 12 MHz) at a flea market. The power supply was dead, the CMOS battery had leaked, and the hard drive made sounds like a coffee grinder.

After recapping the PSU, neutralizing the battery acid with vinegar, and replacing the MFM drive with a XTIDE + CF card adapter, the machine booted into DOS 3.31. The CGA output on a period-correct monitor is a shade of green that no modern display can reproduce.

The restoration looked simple from the outside, but each subsystem had to be proven independently. Old machines fail in clusters: power instability hides logic faults, corrosion causes intermittent behavior, and storage errors can masquerade as software problems.

Restoration sequence that worked

Power path first: PSU recap, rail checks under load, fan reliability.
Board cleanup: remove battery residue, inspect traces, continuity checks.
Minimal boot config: CPU, RAM, video only.
Add peripherals one by one and record outcomes.
Replace spinning rust with CF adapter for safe daily use.

I treat this like incident response, not hobby magic. Predict expected output, test one hypothesis, compare reality, then decide the next step.

What surprised me

The most fragile part was not the CPU or RAM, but edge connectors and sockets. A careful reseat cycle fixed several “ghost bugs.” Also, DOS 3.31 felt faster than memory suggests once disk latency vanished behind solid-state storage. The machine became practical for retro workflows, not just shelf display.