IBM Model F (83-key)

IBM 83-key keyboard (Model F, XT layout)
	IBM 83-key keyboard, German layout
Manufacturer	IBM
Type	Capacitive buckling-spring keyboard
Release date	August 1981 (with the IBM PC)
Interface	5-pin DIN, PC/XT keyboard protocol
Compatible	IBM PC (5150), IBM PC XT (5160)
Model	1501100 (US English); 1501101–1501105 for other layouts

The IBM 83-key keyboard is the keyboard IBM supplied with the IBM PC (5150) and reused for the IBM PC XT (5160). IBM's later technical documentation calls it the "83-key keyboard". Collectors call it a Model F, but Model F is the name of a whole family of IBM capacitive buckling-spring keyboards, and several of them will not work with a 5150.^[1]

The first Model F keyboard was fitted inside the IBM System/23 Datamaster, released a month before the IBM PC. The Datamaster's engineers went on to design the PC and used the same keyboard for it.^[2] Admiral Shark's Keyboards describes the PC keyboard's key assembly as the same as the Datamaster's, with different controller electronics.^[3]

Specifications

IBM's Technical Reference for the 5150 describes the keyboard in Section 4 (p. 4-3):^[4]

Capacitive key technology, with an Intel 8048 microcontroller in the keyboard doing the key scan.
A permanently attached, shielded, coiled five-wire cable about 182.88 cm (6 ft) long, ending in a DIN plug. The wires carry +5 V dc, ground, two bidirectional signal lines and a reset line.
83 keys in three groups: a typewriter layout in the centre, 10 software-defined function keys on the left, and a 15-key pad on the right legended for numeric entry, cursor control, calculator and screen edit.
Two tilt positions, 5 or 15 degrees.
The keyboard sends scan codes, not ASCII. Every key is typematic and sends a make code and a break code; the break code is the make code plus hex 80.
On request from the system unit the 8048 runs a power-on self test of its ROM and memory and checks for stuck keys. It buffers up to 16 scan codes.

IBM offered six layouts: US English, UK English, French, German, Italian and Spanish (p. 4-5).^[4] Deskthority lists the part numbers as 1501100 (US English), 1501101 (French), 1501102 (German), 1501103 (Spanish), 1501104 (Italian) and 1501105 (UK English).^[5]

There are two types. A type 1 keyboard is reset by the motherboard at power-on; a type 2 resets itself. Both work on a 5150, and some type 2 keyboards still have the reset wire connected.^[1] According to Deskthority, the type 1 has a longer internal controller board with extra components, and opening the keyboard is the only sure way to tell the two apart.^[5]

Construction

The key assembly is a curved steel back plate and a curved steel top plate with the switches and a flexible PCB between them. Slots in the PCB locate on pegs in the back plate, so the PCB takes the curve of the plate. The springs and their hammers, which IBM calls pivot plate assemblies, sit in removable barrels that fit into holes in the top plate. The barrels on the PC keyboard have a locating peg; later AT-layout barrels have a notch instead. The two plates are held together by interlocking tabs around the edge, with one longer tab from the top plate folded over the back plate.^[2]^[3]

A key press buckles the spring and tips the hammer down onto a pair of sensing pads on the PCB (the "pad card"), and the controller registers the change in capacitance.^[3] The keycaps are dye-sublimated PBT, all of one profile; the curve of the plates gives the row shape.^[2] The space bar is the only stabilised key, and it cannot be pulled off without opening the keyboard and unhooking its stabiliser wire.^[5]

Foam sheet repair

A perforated foam sheet sits between the switches and the top plate and keeps the two plates under pressure. The foam degrades with age.^[2] Admiral Shark's Keyboards says the usual effect is that keys turn in their barrels more easily, and that the degraded foam becomes a real problem mainly once the assembly has been opened and the old foam allowed to decompress.^[3] So if a keyboard is opened for any reason, have replacement foam ready.

Opening the assembly means unfolding the long tab and working the interlocking tabs apart so that the top plate lifts off the back plate. The barrels, springs and hammers are then free to fall out.^[2] Minuszerodegrees warns that reassembly is the hard part, specifically mating the curved circuit board with the curved metal plate, and points to a video of the job.^[1]

Compatibility

The 84-key keyboard IBM introduced with the IBM PC AT (5170) uses a new keyboard protocol and does not work on a 5150, although the DIN connector is the same.^[1] The US-layout AT keyboard is part number 6450200.^[2]

Some auto-switching IBM 101-key keyboards work on a 5160 but not on a 5150. Minuszerodegrees recommends buying one only with a guarantee that it works on a 5150, and notes that the LEDs and the F11 and F12 keys are not expected to work.^[1] The alternatives are a third-party keyboard with an XT mode, or an AT, PS/2 or USB keyboard with a converter.^[1]

Common faults

No response from the keyboard: check the cable. Minuszerodegrees publishes a diagram for metering it out end to end.^[1]
Keys that twist in their barrels: degraded foam, see above.^[3]
A replacement keyboard that does nothing on a 5150 may simply be the wrong kind (see Compatibility).

References

↑ ^1.0 ^1.1 ^1.2 ^1.3 ^1.4 ^1.5 ^1.6 IBM 5150 – Keyboards, minuszerodegrees.net. Supports IBM's name "83-key keyboard", its reuse on the 5160, the type 1 and type 2 reset behaviour, the reset wire on some type 2 keyboards, the cable metering diagram, the reassembly warning, "Model F" as a family name, the 84-key AT keyboard not working on a 5150, and the caution about auto-switching 101-key keyboards.
↑ ^2.0 ^2.1 ^2.2 ^2.3 ^2.4 ^2.5 IBM Model F, Deskthority wiki (compiled by keyboard collectors). Supports the Datamaster origin, the plate, flexible PCB and barrel construction, the foam sheet, the interlocking tabs, the one-profile PBT keycaps, and part number 6450200 for the US AT keyboard.
↑ ^3.0 ^3.1 ^3.2 ^3.3 ^3.4 IBM Model F keyboards, Admiral Shark's Keyboards (sharktastica.co.uk). Supports the shared Datamaster assembly, the layer order of the assembly, IBM's term "pad card" for the capacitive PCB, the "XT-style" barrels used on the 5150, 5155 and 5160 keyboards, and the effect of foam degradation.
↑ ^4.0 ^4.1 IBM, Technical Reference, Personal Computer Hardware Reference Library, Revised Edition (April 1984), 6322507, Section 4 "Keyboard", pp. 4-3 to 4-5. Hosted as File:IBM PC 5150 Technical Reference.pdf, described at IBM PC 5150 Technical Reference.
↑ ^5.0 ^5.1 ^5.2 IBM Personal Computer keyboard, Deskthority wiki. Supports the six layout part numbers, the type 1 internal PCB, and the space bar that cannot be removed without opening the keyboard.

Related pages

[mzkbd-1] 1.0 ^1.1 ^1.2 ^1.3 ^1.4 ^1.5 ^1.6 IBM 5150 – Keyboards, minuszerodegrees.net. Supports IBM's name "83-key keyboard", its reuse on the 5160, the type 1 and type 2 reset behaviour, the reset wire on some type 2 keyboards, the cable metering diagram, the reassembly warning, "Model F" as a family name, the 84-key AT keyboard not working on a 5150, and the caution about auto-switching 101-key keyboards.

[dtmodelf-2] 2.0 ^2.1 ^2.2 ^2.3 ^2.4 ^2.5 IBM Model F, Deskthority wiki (compiled by keyboard collectors). Supports the Datamaster origin, the plate, flexible PCB and barrel construction, the foam sheet, the interlocking tabs, the one-profile PBT keycaps, and part number 6450200 for the US AT keyboard.

[shark-3] 3.0 ^3.1 ^3.2 ^3.3 ^3.4 IBM Model F keyboards, Admiral Shark's Keyboards (sharktastica.co.uk). Supports the shared Datamaster assembly, the layer order of the assembly, IBM's term "pad card" for the capacitive PCB, the "XT-style" barrels used on the 5150, 5155 and 5160 keyboards, and the effect of foam degradation.

[tr5150-4] 4.0 ^4.1 IBM, Technical Reference, Personal Computer Hardware Reference Library, Revised Edition (April 1984), 6322507, Section 4 "Keyboard", pp. 4-3 to 4-5. Hosted as File:IBM PC 5150 Technical Reference.pdf, described at IBM PC 5150 Technical Reference.

[dtpc-5] 5.0 ^5.1 ^5.2 IBM Personal Computer keyboard, Deskthority wiki. Supports the six layout part numbers, the type 1 internal PCB, and the space bar that cannot be removed without opening the keyboard.

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