IBM Model F (83-key)
| IBM Model F (83-key XT layout) | |
|---|---|
| File:IBM Model F placeholder.png | |
| The 83-key IBM Model F keyboard, supplied with the IBM 5150 and 5160 | |
| Manufacturer | IBM (Lexington, Kentucky plant) |
| Type | Capacitive buckling-spring mechanical keyboard |
| Release date | August 1981 |
| Discontinued | 1985 (replaced by Model M) |
| Interface | 5-pin DIN (XT protocol — not AT-compatible without converter) |
| Compatible | IBM PC (5150), IBM PC XT (5160), any XT-protocol clone |
| Dimensions | 491 × 207 × 57 mm |
| Weight | 2.5 kg (5.5 lb) |
| Model | 4584656, 1801449 (later XT-only revision) |
| Part number | 1801449 / 4584656 |
The IBM Model F (83-key) is the original IBM Personal Computer keyboard, shipped from August 1981 to 1985 with the IBM PC (5150) and IBM PC XT (5160). The 83-key XT layout has F1-F10 in two columns down the left side, no separate cursor cluster (the numeric keypad doubles as cursor keys), and a steel-and-zinc internal construction that makes it one of the heaviest keyboards ever sold.
The Model F is built on the same capacitive buckling-spring switch design as the later IBM Model M, but uses a fully capacitive sense PCB instead of the Model M's membrane. Each key has its own barrel containing a spring that "buckles" sideways when pressed, snapping a flipper into contact with the PCB through a foam-and-foil pad. The result is the famously sharp tactile click that defined the IBM PC keyboard feel.
Hardware
- Switch: capacitive buckling-spring, ~65 cN actuation force, ~3.5 mm travel.
- Steel back plate (1.6 mm) and zinc-cast top frame.
- 83 keys arranged in the XT layout: F1-F10 left column-pair, alphanumerics centre, numeric/cursor pad on the right.
- Internal MCU: Intel 8048-family, generating XT-protocol scan codes.
- Coiled DIN-5 cable to the host.
Foam Pad Repair
The foam-and-foil pads inside each barrel degrade with age — the foam crumbles and the foil oxidises, producing dead or stuck keys. A full restoration replaces all 83 pads with modern equivalents (Modern Model F's "polypads" or laser-cut 3M foil sheets are the usual choice) and removes any residue from the PCB with isopropyl alcohol.
The disassembly sequence is:
- Remove the two case screws on the underside.
- Lift the top shell off; the barrel plate stays with the steel back plate.
- Unbend the C-clips around the barrel-plate perimeter (typically 12-16 clips).
- Lift the barrel plate clear of the PCB.
- Carefully turn the assembly over; the 83 springs and flippers sit loose inside their barrels.
- Replace the foam-and-foil pads, re-bend the C-clips, and reassemble.
The C-clips fatigue with repeated bending — use a soldering iron to spot-weld replacement clips if a clip breaks during reassembly.
Compatibility
The 83-key Model F speaks the XT keyboard protocol — a simple unidirectional serial stream. It will not work with an AT, PS/2, or USB host directly. A small adapter (Soarer's Converter, TMK, or a Pro Micro running tmk_keyboard) translates XT to PS/2 or USB.
The 84-key AT Model F (P/N 6450200, shipped with the 5170 AT) uses the bidirectional AT protocol and is not interchangeable with the 83-key XT version, although the physical case design is similar.
Common Faults
- Dead or stuck keys — foam-and-foil pad degradation. Replace the pads.
- Whole-keyboard 301 error — broken conductor in the curly DIN cable at the strain relief. Replace the cable; the DIN-5 connector is a standard part.
- Spurious key repeats — corroded sense pad PCB. Clean with isopropyl alcohol; re-apply contact cleaner sparingly.
- Yellowed top shell — retrobrite is possible but be cautious of the IBM badge.
Related Pages
- IBM PC (5150)
- IBM PC XT (5160)
- IBM Model M — the membrane-based successor
- Retrobrite