Skip to content

Apple III

Apple's professional flop (1980): a higher-clocked 6502, the SOS OS, an Apple II compatibility mode. Famous for its thermal reliability problems (no fan → chips "walking" out of their sockets). Typical repair: reseat the chips, recap, PSU.

The Apple III (1980), with its built-in floppy drive.
The Apple III (1980), with its built-in floppy drive. Photo: Sailko, CC BY 3.0, via Wikimedia Commons.
The Apple III's motherboard.
The Apple III's motherboard. Photo: Original uploader was Hellis at it.wikipedia, CC BY-SA 3.0, via Wikimedia Commons.

Identification

  • CPU: 6502B @ ~1.4–1.8 MHz; up to 256 KB RAM; a real-time clock (often dead).
  • Video: 80-column text + graphics; composite/RGB output.
  • Media: Disk III drive (built-in) + ProFile hard disk (via interface); Apple III+ = revision.

Repair (technician)

The Apple III's curse: chips creeping out of their sockets

With no ventilation, thermal cycling made the ICs rise out of their sockets (intermittent contacts). The real fix: firmly reseat every socketed chip, and resolder/replace oxidized sockets. (The "lift the machine and drop it" legend = a symptom of the same problem, not a real repair.)

  • Recap (PSU + board) → Recap; mains-filter RIFA.
  • Dead real-time clock: period part → bypass/replace.
  • PSU: classic service (caps, regulation).
  • Disk III drive: mechanism → clean / emulator.

Procedure — a dead computer, step by step ✅

What this adds

Ordered for a home computer: what kills these is its power supply, its battery, its capacitors, its socketed RAM and its keyboard — roughly in that order, and well before the CPU. → PCB diagnosis

1. The power supply — measured before it is plugged in. This is the one step not to swap around. On a machine of this age a supply does not simply stop: a 5 V regulator that fails high puts 7, 9, 12 V onto the bus and takes the RAM and the custom chips with it. Measure every rail off the machine, under a dummy load if you can, and only then plug it in. This page documents RIFA capacitors on this machine: the mains filter caps that crack, then let go in smoke on the first power-up. Replace them before you switch on, not after.

2. The battery, if it has one. Any RTC or backup cell soldered to a board is a future leak. If yours has one and it has never been changed, take it out before it takes the tracks with it. → Backup batteries

3. Capacitors. Recap is the default on these machines, not a last resort — and on the supply first, since that is what protects everything else. → Recap

4. RAM, on its sockets. These machines were built to be repaired: the RAM, and often the logic, sit in sockets. Reseat everything first — thirty years of oxide is a classic no-boot. Then swap chips: a bad RAM chip usually gives a repeatable pattern of garbage or a screen frozen at a fixed character.

5. The keyboard. A console does not have one; a computer's is a wear part. A membrane keyboard fails as whole dead rows or columns — that is the membrane, not the machine. A mechanical one wants its contacts cleaning, not replacing. Check this page: the failure mode is often documented per model.

6. Storage — tape or disk. Both often come down to the same things: a dirty head, and for tape the azimuth and a belt turned to tar. ⚠️ On the floppy side, check whether the mechanism actually has a belt before looking for one: many do, but some drives are direct drive, and hunting a belt that isn't there means stripping a drive for nothing. A machine that boots but loads nothing is a drive fault, not a logic fault — do not go looking on the board for it.

7. Video output. RF, composite, RGB or a dedicated monitor, depending on the machine (see Identification). Test with something else before you conclude: a period modulator and a modern TV disagree far more often than either is broken.

8. Still nothing. Now the logic: rails on the board, reset, clock, bus. → PCB diagnosis

Modernisation & mods — what to buy, how

The 'chips creep out' myth: re-seat + turned-pin sockets

The Apple III is famous for ICs working loose from their sockets (thermal cycling) → re-seat the chips (the notorious "drop the machine a few cm") and, above all, replace the sockets with quality turned-pin ones. Preventive recap.

  • Storage: Floppy Emu (BMOW) 🟢 handles the Disk III (SD card); ProFile hard-disk emulators 🟡 to drop the mechanical drive.
  • Video: composite output 🟢 → modern display via an upscaler; RGB if present.

⚠️ Do not host ROMs/SOS — method only.

See also

Sources & attribution

Image:

Review & corrections

How this space is used

Spotted a wrong value, an outdated procedure, a chip reference that does not match your board? Say so here, with what you observed (model, board revision, serial number, measurement). Every report is cross-checked against a source before anything changes — an unverifiable correction is published as “reported by …, not cross-checked” rather than silently applied.

Reading is open to everyone; posting requires signing in with Discord. Reports from the wiki's declared reviewers are handled first; anyone else's are read too, but go through a human before anything is changed.