IBM 7531 Industrial Computer

Announcement letters
Diagnostics diskette images
System board
System board connections, jumpers, switches

IBM 7531 Industrial Computer


The IBM 7531 Industrial Computer is an Intel 80286-based "AT" computer, mounted in a steel frame and surrounded by a heavy duty housing. It is ventilated by a large fan with a particle filter and is fitted to a base designed to allow the computer to be bolted to the floor. Accordingly, it was designed for use in "industrial plant-floor environments".

The type 7531 is part of the former IBM Industrial Computer line. It is effectively "twinned" with the 7532 Industrial Computer. The 7532 has identical computer specifications to the 7531, but is housed in a rack-mounting case rather than the 7531's floor-mounting case. Both correspond in terms of computer specification to the IBM Personal Computer AT [type 5170]. The 7531 and 7532 directly follow the 5531, an industrial model based around the Personal Computer XT [5160]. The 7537, based on the later Personal System/2 [PS/2] line, supercedes the 7531 and 7532.

The 7531 initially shipped with a 6MHz 80286 processor (later models had an 8MHz 286). The system board shipped with 512KB of memory onboard, with a number of options to extend it with expansion cards.

A video card was considered a prerequisite, however CGA [Color Graphics Adapter] and EGA [Enhanced Graphics Adapter] colour options were available, as the intended monitor [7534 Industrial Graphics Display, also with filtered fans] is capable of EGA modes. (Despite the recommendations and available options, the Technical Reference suggests that a monochrome adapter can be used instead.)

The system shipped by default with a "new" high density 1.2MB 5.25" half height floppy disk drive. Up to two full height 20MB hard disks were available as an option. The controller for the drives was the only expansion card included with the basic configuration.

The keyboard was a then brand-new design (at least for x86 IBM computers as far as I have seen...): the 101 and 102 key layouts that still provide the basis for the vast majority of keyboard layouts today.

The 7531 was never going to be a particularly popular machine, due to its specialised nature. Nevertheless it is an interesting variant of the 5170 AT, which saw the introduction of some interesting features before the IBM Personal Computer line did.

Announcement letters

Original announcements from IBM. Announcement letters from the present back to the early 1980's are searchable at IBM (see resources).

185-053 - US Announcement Letter, May 21st 1985
ZG85-0246 - EMEA Announcement Letter, June 18th, 1985

Diagnostics diskette images

The following are executable self-extracting disk images originally provided by IBM for use with the 7531 and 7532 computers. They were once publically available on the IBM Industrial products website, but are no longer available from IBM. Many thanks to Louis Ohland, who provided working copies of these images.

7531_2CL.EXE - 7531/2 Customer Level Diagnostics
7531_2AD.EXE - 7531/2 Advanced Diagnostics
7531_2KU.EXE - 7531/2 Keyboard Utilities

System board

7531 System Board
The Technical Reference shows a board of similar devices but a different layout.

C26 Variable cap 5-50 pF
J1-J8 I/O channel 62-pin edge connector
(ISA 8 bit)
J10-J14,J16 I/O channel 36-pin edge connector (ISA 16 bit extension)
J9,J15 Not present ("for future use")
J18 RAM jumper
J19 Speaker connector
J20 Power LED and keylock connector
J21 Battery connector
J22 Keyboard connector
PS8,PS9 Power supply connector
SW1 Type of display adapter switch
U2,U3,U8 etc. Mitsubushi M5M4256P 16K [626106-15]
U17,U37 28-pin DIL socket [for EPROM]
U27 IBM 6448896 16Kx8 EPROM
U47 IBM 6448897 16Kx8 EPROM
U61 Sprague 61Z14A200 [PE21213 ("time delay")]
U74 Intel CG80286-6 C
U76 40-pin DIL socket [for 80287 co-processor]
U103 Intel P8254-2
U111 8237A-5
U114 Intel P8259A ("master")
U117 Motorola MC146818
U122 Intel 8237A-5
U124 TI SN74L5612N [L5612]
U125 AMD P8259A ("slave")
U126 Intel D8742 [8042 keyboard controller]
Y1 OSC 14.318MHz
Y2 OSC 12.000MHz

R denotes location of retaining clip
S denotes location of screw
Other circles represent unused (for 7532? 5170?) holes

Much information above (including all quotes) is from the Technical Reference (see directly below).

System board connections, jumpers and switches

The following extracts are directly from:
IBM 7531/2 Industrial Computer Technical Reference System Unit [P/N 6523261]
First Edition (July 1985)
Chapter 1 [System Unit], p. 26,27,51,52,53

I have added images of the devices being discussed, and a few corrections.

Note: Diagrams are oriented as the two system board images, except keyboard connector.
They were approximated from enlargments of the system board outline, which is why they're so blocky.

Other Circuits


The system has a 2-1/4 inch permanent-magnet speaker, which can be driven from:

  • The I/O-port output bit
  • The timer/counter's clock out
  • Both.
  • ED: See below for speaker connector.


    The system board has a three-pin, Berg-strip connector. The placement of a jumper across the pins of the connector determines whether the system board's second 256Kb of RAM is enabled or disabled. Following are the pin assignments for the connector.

    1No connection
    3A8 (28S42)
    J18 RAM Jumper
    RAM Jumper Connection(J18)

    The following shows how the jumper affects RAM.

    Jumper PositionsFunction
    1 and 2Enable 2nd 256Kb of system board ram
    2 and 3 Disable 2nd 256Kb of system board ram

    RAM Jumper

    Note: The normal mode is the enable mode. The disable mode permits the second 256Kb of RAM to reside on adapters plugged into the I/O bus.

    Type of Display Adapter Switch

    The system board has a slide switch, the purpose of which is to tell the system to which display the primary display is attached. Its positions are as follows:

    On (toward the front of the system unit)

    The primary display is attached to the Color/Graphics Monitor Adapter.

    Off (toward the rear of the system unit)

    The primary display is attached to the Monochrome Display and Printer Adapter.

       Note: The primary display is activated when the system is turned on.

    1-26  System Unit
    Other Circuits (continued)

    Variable Capacitor

    The system board has a variable capacitor. Its purpose is to adjust the 14.31818MHz oscillator (OSC) signal that is used to obtain the color burst signal required for color televisions.

    ED: Variable cap peeks through a metal plate, with Y1, among other things, hiding underneath.
    Variable capacitor location
    Chapter 1   System Board   1-27 


    The system board has the following connectors:

  • Speaker connector (J19)
  • Two power-supply connectors (PS8 and PS9)
  • Keyboard connector (J9 J22*)
  • Power LED and keylock connector (J20)
  • Battery connector (J21).
  • [* J9 is one of the non-existant ["for future use"] 36-pin I/O connectors.]

    The speaker connector is a 4-pin, keyed Berg strip. The pin assignments follow.

    The pin assignments for power-supply connectors, P8 PS8 and P9 PS9, are as follows:

    1Data out
    4+5 Vdc
    Speaker Connector (J19)
    J19 Speaker Connector
    1Power good
    2+5 Vdc
    3+12 VdcPS8
    4-12 Vdc
    3-5 VdcPS9
    4+5 Vdc
    5+5 Vdc
    6+5 Vdc
    PS8,PS9 Power Supply Connectors
    Power Supply Connectors
    ED: Connectors and sockets are keyed to prevent accidental frying. On my example, cable 1 for PS8 is marked for instant distinguishing.

    Chapter 1   System Board   1-51 

    The keyboard connector is a 5-pin, 90-degree Printed Circuit Board (PCB) mounting, DIN connector. The pin assignments are as follows:

    1Keyboard clock
    2Keyboard data
    5+5 Vdc
    J22 Keyboard Connector
    Keyboard Connector (J22)

    The power LED and keylock connector is a 5-pin Berg strip. Its pin assignments are as follows:

    1LED Power
    4Keyboard Inhibit
    J20 Power LED and Keylock Cnnector
    Power LED and Keylock Connector (J20)

    The battery connector is a 4-pin, keyed Berg strip. The pin assignments are as follows:

    2Not Used
    3Not Used Key*
    46 Vdc.
    J21 Battery Connector
    Battery Connector (J21)
    [* The pin is absent and the battery connector is keyed.]

    1-52  System Unit

    The following figure shows the layout of the system board.

    System Board Layout


    Chapter 1   System Board   1-53 
    Diagrams of connectors and switches to be added.


    Open the case

    First, pull out the fan filter. Find and remove three screws on each side attaching the metal housing to the pedestal base (or in my case, find them missing). Locate two recesses at bottom of rear bezel and remove screws within (or discover them AWOL too). From the front of the computer pull the main body away, pushing upwards if it sticks. It will move clear of the rear bezel, with the front bezel remaining attached. The body should slide right off (and back on again).

    Remove computer from floor mount

    With the case open, remove the two screws holding the fan filter slot/guide on the left hand side (a driver with a 3/16" or 5mm hex socket makes light work of them). Then, on the other side of the machine, remove the four prominent screws in square formation (5/16" hex socket). Disconnect everything from the grounding point on top (3/16" again), and unhook the power cord from the power supply and thread it out of the way. From the front, grip the internal "box" [right hand in the recess on the right, left just behind the power supply] and slowly slide it forwards. The "box" alone is heavier [">18Kg (40lb)"] than the floor mount, so be ready to take the weight as you slide it off. It slides back into place in the reverse manner.

    Remove system board

    Pull cards and disconnect cables (you'd never guess). Remove pair of screws [marked S] (3/16" hex socket), next to J8 [ISA slot] and J18 [RAM jumper] (one each). Squeeze the two retaining clips [marked R] in corners on left and lift board above. Repeat with remaining clips. With all clips clear, slide system board out.


    IBM Announcement Summary
    - hit "Search Announcements" on the left to search the Announcement Letter archives.

    Industrial Computers and Displays
    - mirror of IBM Industrial Products website from 1996.

    IBM Archives: IBM 7535 Manufacturing System
    - IBM archive exhibit demonstrating type 7535 robot (albeit connected to an IBM PC and not an IBM Industrial Computer)

    Industrial Computers
    - Industrial Computers index at Louis Ohland's "Ardent Tool of Capitalism"

    - Various photographs of my 7531-041, 7534-002 and P/N 1388076 (in harsh industrial environments)

    This page gathered together by Daniel Wright [dw_junon of]
    I look forward to your complaining and pillaging.
    Generic psuedolegal disclaimer.
    Last touched 2007-04-10 15:29 UTC