IBM 5151

{Infobox computer peripheral | name = IBM Monochrome Display | image = | caption = IBM monitors, left to right: 5151 monochrome, 5153 colour, 5154 Enhanced Color Display | manufacturer = IBM | type = TTL monochrome CRT monitor | release_date = 1981 (with the original IBM PC) | interface = TTL digital, 9-pin D-shell (driven by the IBM Monochrome Display Adapter) | compatible = IBM PC (5150), IBM PC XT (5160), IBM PC AT (5170), MDA- and Hercules-compatible systems | dimensions = 280 mm H × 380 mm L × 350 mm D | weight = 7.9 kg (17.3 lb) | model = 5151 }

The IBM 5151, which IBM called simply the IBM Monochrome Display, is the green-phosphor TTL monitor sold with the original IBM PC (5150) when it was ordered with the IBM Monochrome Display Adapter (MDA). It displays 80 × 25 text only — it has no graphics capability — but the MDA's large 9 × 14 character box gives an image of 720 by 350 addressable dots, which is why MDA text is visibly sharper than CGA text.

Display Characteristics

IBM's own figures:^[1]

CRT: 28.3 cm (11.5 in) diagonal, 90° deflection.
Phosphor: P39, high persistence, green. Long persistence suppresses flicker at the 5151's low refresh rate, at the cost of smearing on moving content.
Screen surface: etched to reduce glare.
Presentation: 80 characters wide by 25 rows deep, each character defined in a 14 PEL high by 9 PEL wide matrix.
Vertical drive: screen refreshed at 50 Hz, with 350 lines of vertical resolution and 720 lines of horizontal resolution.
Horizontal drive: positive-level, TTL-compatible, at 18.432 kHz.
Video bandwidth: 16.257 MHz maximum at −3 dB.
Heat output: 325 BTU/hr. Cables: 0.914 m power, 1.22 m signal.

Measured at the adapter, the MDA horizontal sync is an 8 µs positive-going pulse every 54.3 µs and the vertical sync is an 850 µs negative-going pulse every 20 ms.^[2]

The 5151 will not work with a CGA card: CGA runs its horizontal scan at 15.75 kHz, well outside the 5151's fixed 18.432 kHz.^[2]

Power

The 5151 has no mains cord of its own. It takes both its signal and its power from the system unit: the signal cable comes from the display adapter, and a second cable takes ac power from a non-standard switched socket on the rear of the PC's power supply, so that the system unit's power switch controls the display.^[1] That outlet can supply a maximum of 0.75 A and IBM states it is intended only for this display.^[3]

Two models were made, a 110 Vac model and a 220/240 Vac model, and IBM's Options and Adapters section carries a separate full schematic for each.^[1]

Input Connector

A 9-pin D-shell at standard TTL levels — 0.0 to 0.6 Vdc at down level, +2.4 to 3.5 Vdc at up level.^[4]

**MDA / 5151 9-pin connector**
Pin	Signal
1	Ground
2	Ground
3, 4, 5	Not used
6	+ Intensity
7	+ Video
8	+ Horizontal sync
9	− Vertical sync

Pins 3, 4 and 5 being physically absent from the plug is normal, not damage — they are unused in the MDA standard.^[5]

The display's three brightness levels (off, normal, bright) come from the combination of the Video and Intensity lines, not from an analogue video level.^[4]

Common Faults

Stiff brightness and contrast knobs. Known behaviour on a healthy 5151, and probably deliberate. Not a fault.^[5]
Stable raster with the brightness turned up, but no characters. On a 5151 specifically, a stable raster proves the monitor is receiving correct horizontal and vertical sync from the MDA card. Work through: contrast set too low; a faulty MDA card that generates sync but no video; an open video wire in the cable; a poor connection on pin 7 at the plug; then the video path inside the monitor. IC201, an SN7406A, has been reported failed by more than one owner.^[5]
No display at all, not even a raster. The 5151 needs an incoming horizontal sync signal from a working, initialised MDA card to produce any raster at all. Before condemning the monitor, check that the card is present, seated and initialised — motherboard switch settings that select EGA instead of MDA will leave it uninitialised.^[5]
Full or partial vertical collapse. A known symptom with published circuit and waveform references.^[5]
Bright spot or line when switching off. Known behaviour, not a fault.^[5]
Dim or shrunken raster, or geometry that drifts as the set warms up. Points at ageing electrolytics on the analogue board. See Capacitor Failure Symptoms.

A self-inflicted fault worth knowing about

Because of the way the 5151 is designed, an improper horizontal sync signal can damage it — and software alone is enough to produce that situation by reprogramming the 6845 on the MDA card outside MDA timings.^[5] Do not run 6845 timing experiments, Hercules-mode software or untested demos against a 5151 you care about.

CRT Safety

The 5151's CRT retains a lethal anode charge after the set is switched off and unplugged, and its mains-derived circuitry sits at line potential while it is running. Discharge the tube before working inside it — see CRT Discharge Procedure.

References

↑ ^1.0 ^1.1 ^1.2 IBM, IBM Monochrome Display, Options and Adapters section, Personal Computer Hardware Reference Library — hosted on this wiki as File:IBM Options and Adapters - IBM Monochrome Display (5151).pdf. "Description" and "Specifications": the two-cable arrangement with power taken from the system unit, the 28.3 cm (11.5 in) diagonal 90-degree-deflection CRT, P39 high-persistence green phosphor with an etched anti-glare surface, 80 characters by 25 rows in a 14 PEL high by 9 PEL wide matrix, maximum video bandwidth 16.257 MHz at −3 dB, 50 Hz vertical refresh with 350 lines vertical and 720 lines horizontal resolution, positive-level TTL horizontal drive at 18.432 kHz, and the physical specifications quoted here. Also documented here as IBM Options and Adapters - IBM Monochrome Display.
↑ ^2.0 ^2.1 IBM: MDA / CGA / EGA, minuszerodegrees.net. Source for the side-by-side 9-pin assignments and for the measured sync pulse shapes: MDA, an 8 us positive-going horizontal pulse every 54.3 us and an 850 us negative-going vertical pulse every 20 ms; CGA, a 4 us positive-going horizontal pulse every 63.7 us and a 190 us positive-going vertical pulse every 16.7 ms.
↑ IBM, IBM 5150 Technical Reference — hosted on this wiki as File:IBM PC 5150 Technical Reference.pdf and documented as IBM PC 5150 Technical Reference. Section 1 "System Board" for the ROM and RAM subsystems; Section 3 "Power Supply", pages 3-3 to 3-6, for the 63.5 W continuous rating, the four dc outputs and their load and regulation figures, the −5 V dynamic-memory bias role, the switched 0.75 A ac outlet provided only for the IBM Monochrome Display, the overvoltage and overcurrent behaviour, the five-second minimum off time and the under- and over-voltage sense levels; Section 4 "Keyboard" for the capacitive keyboard, its Intel 8048, the permanently attached coiled five-wire cable, the 83-key layout, the scan-code protocol and the keyboard's own power-on self test.
↑ ^4.0 ^4.1 IBM, IBM Monochrome Display and Printer Adapter, Options and Adapters section, Personal Computer Hardware Reference Library — hosted on this wiki as File:IBM Options and Adapters - IBM Monochrome Display and Printer Adapter.pdf. Source for the Motorola 6845 CRT controller, the 4 KB display buffer with no parity, the two-bytes-in-553 ns fetch giving 1.8 MB/s, the 8 KB character generator holding 256 codes, the 9 PEL by 14 PEL character box carrying a 7 PEL by 9 PEL character, the 18 kHz monitor requirement, the statement that the adapter does not support a light pen with a P39-phosphor display, the register map, the 9-pin connector pin assignments and TTL signal levels, and the printer-adapter half with its 12 latched outputs and 5 steady-state inputs. Also documented here as IBM Options and Adapters - IBM Monochrome Display and Printer Adapter.
↑ ^5.0 ^5.1 ^5.2 ^5.3 ^5.4 ^5.5 ^5.6 IBM 5151 — Known Problems/Issues, minuszerodegrees.net. Source for the stiff brightness and contrast controls being normal, the raster-but-no-video diagnosis, the reported IC201 (SN7406A) failures, the vertical collapse and switch-off bright line notes, the statement that pins 3, 4 and 5 are absent from the connector by design, and the warning that an improper horizontal sync signal can damage the 5151.

Related Pages

IBM Monochrome Display Adapter — the adapter that drives the 5151
IBM 5153 — the colour equivalent
IBM PC (5150) · IBM PC XT (5160) · IBM PC AT (5170)
IBM Options and Adapters - IBM Monochrome Display — IBM's own specification, hosted here
CRT Discharge Procedure · Capacitor Failure Symptoms

[oa5151-1] 1.0 ^1.1 ^1.2 IBM, IBM Monochrome Display, Options and Adapters section, Personal Computer Hardware Reference Library — hosted on this wiki as File:IBM Options and Adapters - IBM Monochrome Display (5151).pdf. "Description" and "Specifications": the two-cable arrangement with power taken from the system unit, the 28.3 cm (11.5 in) diagonal 90-degree-deflection CRT, P39 high-persistence green phosphor with an etched anti-glare surface, 80 characters by 25 rows in a 14 PEL high by 9 PEL wide matrix, maximum video bandwidth 16.257 MHz at −3 dB, 50 Hz vertical refresh with 350 lines vertical and 720 lines horizontal resolution, positive-level TTL horizontal drive at 18.432 kHz, and the physical specifications quoted here. Also documented here as IBM Options and Adapters - IBM Monochrome Display.

[mzpins-2] 2.0 ^2.1 IBM: MDA / CGA / EGA, minuszerodegrees.net. Source for the side-by-side 9-pin assignments and for the measured sync pulse shapes: MDA, an 8 us positive-going horizontal pulse every 54.3 us and an 850 us negative-going vertical pulse every 20 ms; CGA, a 4 us positive-going horizontal pulse every 63.7 us and a 190 us positive-going vertical pulse every 16.7 ms.

[tr5150-3] IBM, IBM 5150 Technical Reference — hosted on this wiki as File:IBM PC 5150 Technical Reference.pdf and documented as IBM PC 5150 Technical Reference. Section 1 "System Board" for the ROM and RAM subsystems; Section 3 "Power Supply", pages 3-3 to 3-6, for the 63.5 W continuous rating, the four dc outputs and their load and regulation figures, the −5 V dynamic-memory bias role, the switched 0.75 A ac outlet provided only for the IBM Monochrome Display, the overvoltage and overcurrent behaviour, the five-second minimum off time and the under- and over-voltage sense levels; Section 4 "Keyboard" for the capacitive keyboard, its Intel 8048, the permanently attached coiled five-wire cable, the 83-key layout, the scan-code protocol and the keyboard's own power-on self test.

[oamda-4] 4.0 ^4.1 IBM, IBM Monochrome Display and Printer Adapter, Options and Adapters section, Personal Computer Hardware Reference Library — hosted on this wiki as File:IBM Options and Adapters - IBM Monochrome Display and Printer Adapter.pdf. Source for the Motorola 6845 CRT controller, the 4 KB display buffer with no parity, the two-bytes-in-553 ns fetch giving 1.8 MB/s, the 8 KB character generator holding 256 codes, the 9 PEL by 14 PEL character box carrying a 7 PEL by 9 PEL character, the 18 kHz monitor requirement, the statement that the adapter does not support a light pen with a P39-phosphor display, the register map, the 9-pin connector pin assignments and TTL signal levels, and the printer-adapter half with its 12 latched outputs and 5 steady-state inputs. Also documented here as IBM Options and Adapters - IBM Monochrome Display and Printer Adapter.

[mz5151-5] 5.0 ^5.1 ^5.2 ^5.3 ^5.4 ^5.5 ^5.6 IBM 5151 — Known Problems/Issues, minuszerodegrees.net. Source for the stiff brightness and contrast controls being normal, the raster-but-no-video diagnosis, the reported IC201 (SN7406A) failures, the vertical collapse and switch-off bright line notes, the statement that pins 3, 4 and 5 are absent from the connector by design, and the warning that an improper horizontal sync signal can damage the 5151.

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