IBM PS/1 Model 2121

IBM's PS/2 line of computers was targeted towards business and high-performance applications. In 1990 IBM released a new line of low-end computers for home applications. First units, Model 2011, had 286 but later ones had 386 and even 486. Most PS/1 types had normal ISA slots instead of MCA and had simpler design. To make computing easier, early PS/1 computers have parts of software in ROM.
It was possible to fit many upgrades to PS/1. RAM was expandable with special card, it was possible to add expansion boards using 2 16-bit ISA slots, there was also expansion connector in the rear. It was possible to use different mouse and keyboard. IBM offered "Enhanced" mouse and keyboard versions. Such keyboards were smaller and mice more ergonomic than standard ones.

Manufacturer IBM

Origin USA
Year of unit 1991
Year of introduction 1990
Class AT
CPU Intel 80386SX
Speed 16MHz
RAM 2MB (expandable with proprietary card)
ROM PC BIOS, software launcher (called 4-Quad menu)
Graphics VGA
Sound PC Speaker
System expansion bus 16-bit ISA (2 slots)
Floppy/removable media drives 1.44MB floppy disk drive (proprietary connector)



Hard disk: 42MB IDE (PATA)

Peripherals in collection:
 - IBM Standard Keyboard and Mouse
 - IBM Extended Keyboard and Mouse
 - Original monitor
 - Connectivity handset (non-IBM)

Other cards:


DYSP (Dyspozytorka) connectivity/telecommunication card
Non-standard expansions: Telephone connectivity
Operating system(s): MS-DOS

My units are from army surplus, in which they were used as communication devices. They were equiped with special ISA expansion cards giving telephone connectivity and simple modulation for transmitting messages. This system has been used in early 1990s until 2000s in some Polish hospitals. I've made an attempt to describe system components. The systems of course came to me fully sanitized, so if you have a software to operate these cards, you can drop me a line.

Contents: Starting, usage Pinouts CRT Disassembly Links


This model has quite big problem with starting when CMOS backup battery is exhausted. Generally when battery is dead, you will end with errors 16x (161, 163) and booting to ROM. In most units hard disk doesn't contain OEM software (yet it can be found on backups, see links), so ROM software launcher won't launch anything. If you press Ctrl-Alt-Del then you will restart system and it should boot from hard disk. Nevertheless, it won't boot from floppy when started from dead battery state.
If you have a dead battery, RTC may just not tick - sometimes time set doesn't change, it's the main symptom of bad RTC battery. The battery is located on the mainboard under expansion port PCB. Disconnect ribbon cable and you have it.
To make the system boot from floppy, you have to boot DOS somehow and run CUSTOMIZ.EXE program. This program changes settings responsiible for starting and booting the computer. It allows to select boot options, e.g. to try floppy, then hard disk skipping ROM. To run my unit, I had to prepare hard disks in an other computer and add CUSTOMIZ.EXE and CONFIGUR.EXE. The second program, CONFIGUR.EXE is for changing parameters of ports and integrated devices, like "Integrated peripherals" section of Award BIOS Setup program.





Important Pinouts:

Power supply pinout:
The system has power supply and speaker built in monitor. Monitor is a standard VGA with speaker and DC power supply. The pinout is shown below:

(male connector in the computer)
1,2,9 - +33V DC
3,7,10,11,14,15 - GND
6 - PC Speaker out

The voltage is 33V (some sources: 32V) DC, I don't know current, but if you try to run it, give it 1,5A or more and try monitoring 5V and 12V in HDD Molex plug. The computer has a switching converter which makes all needed voltages from 33V DC.




Monitor disassembly:

If you have this computer, remember to clean CRT monitor inside. This monitor has a fan built-in, so after few years of operation you may end with something like this:

To open a monitor, disconnect it from computer and place it on the screen using carpet, cloth or other protective pad.
You also need a special Torx screwdriver with a hole inside. Remove two such screws from the upper part.
Now squeeze two latches and lift the stand from monitor. You will see 2 Philips screws, after removing them you can remove monitor stand's base. Then you will see chassis inside.
Now remove 3 Torx screws and lift the rear cover upwards. Be careful with rubber pads, as they may fall off the cover. Carefully clean the bottom and place the monitor on it. All screws inside are Philips type. Remove 5 of them and lift the part with holes off the chassis. Then you can clean wires and parts of PCB. Use a brush and vacuum cleaner.
To remove fan, unscrew it from the left side. Now clean power supply as much as you can, it is quite difficult to get inside but brushing through holes is sufficient. Remember to clear (using vacuum cleaner) air inlet in the bottom-rear, as there usually is much dust in it.

Links:  - Earlier model 2011 page. There are diagnostic disks, Configuration tools and OEM HDD contents to download, as well as emulator with quite realistic GUI.  - Information about models - Main information about PS/1 computers.