I recently acquired an IBM PS/2 L40 SX laptop which needed some work. This machine is IBM's second ever laptop machine (with the first being the IBM 5140 "PC Convertible"). The specifications include:
This battery has NiCd chemistry and is long dead. NiCd batteries tend to leak and should be removed.
It would originally retain memory contents during battery hot swaps. I permanently removed this and
will not be replacing it.
The original backup battery is a Panasonic BR-2/3A (nominally 3 volts, 1.2 Ah capacity), with its terminals
attached to two short cables terminating in a JST connector. The battery itself is encased in a foam cylinder
and it sits freely inside the machine, not fastened to anything.
To replace the battery, I cut its cables and soldered them to the terminals of a CR-123 battery socket.
I chose the abundant CR-123 as substitute for the original backup battery due to their identical dimensions and similar capacities.
I wrapped the socketed battery in antistatic bubble wrap and placed it wherever it fit.
Where capacitors had leaked, I neutralised the corrosive by scrubbing with vinegar, then cleaning with isopropyl alcohol.
I made a list of the electrolytic capacitors in this machine and their parameters, available here.
One board inside the display (Toshiba LZQ1751-E0HC) has a row of 7 identical capacitors, and this board is attached directly to the LCD matrix.
Instead of removing this board and risking irrepairable damage, I cut the legs off all the capacitors, cleaned up and soldered new ones from the top.
The left image is the before, and the right is the after.
I downloaded and altered the mounting bracket produced by
Butane_Murphy on Thingiverse. The bracket as it is, had screw holes on the sides, while the original disk
is screwed at the bottom, so holes had to be introduced. A cutout was added to make the SD slot accessible and
make routing an SD card extender possible. The photos demonstrate the situation.
3D model download:
SD_HD_sled_l40sx.stp Based on Butane_Murphy's work, altered by nthpulse. CC BY 4.0
The L40 SX requires parity RAM, and will not work with non-parity memory modules (I tried). Parity RAM can be
identified by a module having memory chips in multiples of three.
The modules I used were an identical pair
of 4 MB memories, which have 6 chips on each side.
This laptop (and some other IBMs) have slightly non-standard
SIMM slots, with a longer key than a standard slot. This prevents any regular SIMM from being installed, so
the slot's key must be cut down, or a memory module's notch must be filed deeper.
IBM PS/2s had a unique requirement that memory modules had four "presence detect" bits set, according to size and speed.
This page on ardent-tool.com contains a table titled
"PD Bits SIMM Identification - IBM Parity Modules" which contains the various combinations the bits can be set to.
When modifying memories for the L40 SX, look at the asterisks and their associated notes to find the correct configuration
(this machine deviates a little from the table).
The module on the left has been set to 4MB and the other is set to 2MB. Two 4MB modules are not supported, so one has to
be 2MB. This gives a total of 8MB memory (2MB onboard + 2MB + 4MB).
I designed and 3D printed a floppy disk drive faceplate using photos from the internet as visual references. Having no faceplate makes
aligning a disk during insertion slightly annoying.
3D model:
L40SX FDD faceplate RSDOCX
L40SX FDD faceplate STL
The L40SX FDD faceplate files are placed in the public domain.
Created: 08APR2025
Last modified: 05JUL2025