IBM Personal System/2 Laptop 40 SX (PS/2 L40SX) Notes

Overview

The L40 SX was announced on March 26, 1991. Here are some highlights from the announcement letter:

Standard features:

20Mhz 80386SX CPU
2MB of 80ns memory expandable to 18MB
60MB hard drive
3.5" 1.44MB floppy drive
VGA resolution LCD (10 inches, Supertwisted Nematic LCD, 640x480)
Ports: Serial, parallel, keypad/mouse, external VGA monitor, and an expansion connector.
17 key external numeric keypad
Socket for an 80387SX numerical co-processor
Included accessories: AC adapter, rechargeable battery pack and a carrying case.
Weight: 7lbs, including the battery.

Options:

Data and fax modem (2400 bps for data, 9600 bps for fax, Hayes command set)
A second serial port
Trackpoint pointing device (can be used as a trackball or a mouse)
2, 4, or 8MB memory upgrades
Quick charger
Car power adapter

The machine was targeted at mobile professionals with an initial price of $5995 for the base model without options, which would be over $11,300 in 2020 equivalent dollars. To put things in perspective, a base model 1991 Nissan Sentra had a manufacturer's suggested retail price of $8290. The 2MB memory upgrade started at $899, while the 8MB memory upgrade was an eye-popping $3595.

Prices dropped several times during the life of the machine:

1991-07-25: $5245
1991-10-02: $3955
1991-11-19: $3645
1992-02-11: $2495
1992-05-02: $1965

On July 9th, 1992 IBM withdrew the PS/2 Model L40 SX from marketing, making it available for sale for a little over 15 months.

Technical Notes

Here are some things to keep in mind with these machines:

Batteries

There are three batteries on these machines:

A large NiCD battery pack for portable use of the machine. These are all probably dead now and should be rebuilt with NiCD cells if you are going to try to use the machine as a portable machine.
A CMOS battery to preserve the CMOS settings while the machine is powered off. The original (and correct) battery is a Panasonic BR-2/3A which is a 3 volt Lithium battery, available from Digikey for around $5 USD. Do not use a CR-123A photo battery; the size and voltage are fine but it will not last as long.
A memory standby battery which is a 3.6V NiCD pack rated for 45mAH. The machine will run fine if this battery is dead but you will not be able to swap the main battery without this battery functioning. (I only use the machine when connected to AC power so this is not an issue for me.)

Hard Drives

IBM originally sold the machine with a 60MB Conor hard drive. Surprisingly, the hard drive is a standard 2.5" IDE mobile drive. If you find a machine with the original hard drive you can assume it is dead; I've only seen one surviving original hard drive.

While the hard drive is a standard IDE hard drive, the ribbon cable that connects the drive to the motherboard is not standard and it is very fragile. Be careful working with it.

If you have to replace the hard drive don't use a mechanical hard drive. Use a Disk-On-Module or an industrial Compact Flash card. See "Upgrading an IBM L40 SX to an SSD" for the procedure.

Memory

The standard machine came with 2MB of memory on the motherboard. Two memory slots allow for expansion to a maximum of 18MB. The memory is not standard so you have to find the exact part numbers. The memory upgrades were expensive options so finding a machine with a lot additional memory is unusual.

Communications Cartridge I

The Communications Cartridge I (model 3541-001, 06G8050) is an option that allows one to use the L40 SX to connect to midrange or mainframe computers. The device itself is a self-powered bus expansion that holds one short 8-bit ISA card and connects to the L40 SX using a thick cable. Originally intended for use with Token Ring adapters, 3270 emulation cards or 5250 emulation cards, it also can work with other ISA cards such as Ethernet or SCSI cards.

The announcement letter for the L40 SX indicated that an option like this would be available. It was finally announced on October 17th, 1991. These were originally priced at $595 so you won't find too many of them in the wild.

Cards known to work:

IBM Token Ring (PN 25F7367), from the announcement letter
IBM 3270 (PN 53F6425), from the announcement letter
IBM 5250 (PN 49F5618), from the announcement letter
Generic NE1000 Ethernet card, tested personally
Future Domain TMC-850IBM SCSI card, tested personally

Notes:

The connectors are consist of two rows each with 60 pins. Both end of the cable are male. The cable side mail connectors look to be AMP 6-175473-1 and the device side female connectors look to be AMP 6-175474-1.


Internal circuit board, top view	Internal circuit board, bottom view	Bus connector cable

Resources

Here are some resources that you will find useful for your L40 SX.

(Special thanks to John Roth who provided the paper marketing brochure, the keyboard templates, the L40 SX Presentation guide, and the Communications Cartridge instructions.)

Keyboard template:

IBM provided blank templates that you could write on to remind yourself of the special key combinations of programs you were using. (Right click to save the full sized image.)

IBM L40 SX Keyboard Template

IBM announcement letters:

IBM PS/2 L40 SX Announcement Letter (edited and formatted slightly better)
IBM PS/2 Communications Cartridge Announcement Letter (edited and formatted slightly better)

Reference Diskettes:

IBM PS/2 Model L40 SX Reference Diskette version 1.00 (IBM_L40SX_Reference_Diskette_100_image.dsk) (1991-01-30, superseded)
IBM PS/2 Model L40 SX Reference Diskette version 1.01 (IBM_L40SX_Reference_Diskette_101_image.dsk) (1991-09-01, superseded)
IBM PS/2 Model L40 SX Reference Diskette version 1.03 (IBM_L40SX_Reference_Diskette_103_image.dsk) (1992-02-19, latest)

These are a standard 1.44MB diskette images. You can create a 3.5" diskette from these images using dd (Linux), WinImage (Windows), or DskImage (DOS).

Documentation:

IBM PS/2 Model L40 SX Brochure (IBM_L40SX_Brochure.pdf): A marketing brochure (930KB)
IBM PS/2 Model L40 SX Presentation Guide (IBM_L40SX_Presentation_Guide.pdf): A marketing presentation with speaker notes (5.6MB)
IBM PS/2 Model L40 SX Quick Reference (IBM_L40SX_Quick_Reference.pdf): Quick reference guide, originally from http://hpholm.dk/pdf/L40SX_Quick_Reference.pdf (962KB)
IBM PS/2 Model L40 SX Reference Summary (IBM_L40SX_Reference_Card.pdf): A much smaller quick reference card (491KB)
IBM PS/2 Communications Cartridge Installation and Operating Instructions (IBM_Communications_Cartridge.pdf): Installation and operating instructions for the Communications Cartridge, which is basically a bus expansion for the L40 SX. (2.4MB)

External Links:

A great page full of information on the L40 SX: https://www.ardent-tool.com/8543/8543.html
Another good page with information on the L40 SX: http://hpholm.dk/L40SX.html
A reasonably good tear-down video: https://www.youtube.com/watch?v=h4QNxhlCHFo
My hard disk replacement instructions for the L40 SX: http://www.brutman.com/L40SX_DOM/L40SX_DOM_Upgrade.html

Created August 16th, 2020, Last updated November 26th, 2020
(C)opyright Michael B. Brutman, mbbrutman at gmail.com