Editing IBM 5151

{{Infobox computer peripheral
| name          = IBM Monochrome Display
| image         = [[File:IBM 5151 5153 5154 monitors.jpg|260px]]
| 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-compatible systems
| dimensions    = 280 mm H &times; 380 mm L &times; 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&nbsp;&times;&nbsp;25 text only &mdash; it has no graphics capability &mdash; but the MDA's large 9&nbsp;&times;&nbsp;14 character box gives an image of 720 by 350 addressable dots, which is why MDA text is visibly sharper than [[IBM Color Graphics Adapter|CGA]] text.

== Display Characteristics ==

IBM's own figures:<ref name="oa5151">IBM, ''IBM Monochrome Display'', ''Options and Adapters'' section, Personal Computer Hardware Reference Library &mdash; 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 &minus;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]].</ref>

* '''CRT:''' 28.3 cm (11.5 in) diagonal, 90&deg; 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 &minus;3 dB.
* '''Heat output:''' 325 BTU/hr. Power cable 0.914 m, signal cable 1.22 m.

Measured at the adapter, MDA horizontal sync is an 8&nbsp;&micro;s positive-going pulse every 54.3&nbsp;&micro;s and vertical sync is an 850&nbsp;&micro;s '''negative'''-going pulse every 20&nbsp;ms.<ref name="mzpins">[https://www.minuszerodegrees.net/mda_cga_ega/mda_cga_ega.htm 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.</ref>

The 5151 will '''not''' work with a [[IBM Color Graphics Adapter|CGA]] card: CGA scans horizontally at 15.75 kHz, well outside the 5151's fixed 18.432 kHz.<ref name="mzpins" />

== Power ==

The 5151 has '''no mains cord of its own'''. It takes both signal and 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 the system unit's power switch controls the display.<ref name="oa5151" /> That outlet supplies a maximum of 0.75 A and IBM states it is intended only for this display.<ref name="tr5150">IBM, ''IBM 5150 Technical Reference'' &mdash; 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 &minus;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.</ref>

Two models were built, a 110 Vac model and a 220/240 Vac model, and IBM's ''Options and Adapters'' section carries a separate full schematic for each.<ref name="oa5151" />

== Input Connector ==

A 9-pin D-shell at standard TTL levels &mdash; 0.0 to 0.6 Vdc at down level, +2.4 to 3.5 Vdc at up level.<ref name="oamda">IBM, ''IBM Monochrome Display and Printer Adapter'', ''Options and Adapters'' section, Personal Computer Hardware Reference Library &mdash; 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]].</ref>

<templatestyles src="Template:StyledTable/styles.css" />
{| class="wikitable styled-table" style="width:60%; text-align:center;"
|+'''MDA / 5151 9-pin connector'''
! Pin !! Signal
|-
| 1 || Ground
|-
| 2 || Ground
|-
| 3, 4, 5 || Not used
|-
| 6 || + Intensity
|-
| 7 || + Video
|-
| 8 || + Horizontal sync
|-
| 9 || &minus; Vertical sync
|}

'''Pins 3, 4 and 5 being physically absent from the plug is normal''', not damage &mdash; they are unused in the MDA standard.<ref name="mz5151">[https://www.minuszerodegrees.net/5151/problems/5151_known_problems_issues.htm IBM 5151 &mdash; 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.</ref>

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.<ref name="oamda" />

== Common Faults ==

* '''Stiff brightness and contrast knobs.''' Known behaviour on a healthy 5151, and probably deliberate. Not a fault.<ref name="mz5151" />
* '''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 generating 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.'''<ref name="mz5151" />
* '''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 &mdash; motherboard switch settings that select EGA instead of MDA leave it uninitialised.<ref name="mz5151" />
* '''Full or partial vertical collapse.''' A known symptom, with circuit diagrams and expected waveforms published for the vertical deflection stage.<ref name="mz5151" />
* '''Bright spot or line when switching off.''' Known behaviour, not a fault.<ref name="mz5151" />
* '''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''' &mdash; and software alone is enough to produce that situation, by reprogramming the 6845 on the MDA card outside MDA timings.<ref name="mz5151" /> Do not run 6845 timing experiments or untested display software 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 &mdash; see [[CRT Discharge Procedure]].

== References ==

<references />

== Related Pages ==

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

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[[Category:IBM]]