Restoring an IBM AS/400 (9401-150)
June 10, 2021
IBM AS/400s are legendary mainframes still present in many companies. In this article I detail how I completely restored an AS/400 9401-150 server.
Analysis and repair of an IBM Model M keyboard
Table of contents :
Introduction
The IBM Model M is an iconic mechanical keyboard produced by IBM since 1985. It is considered one of the best keyboards ever made thanks to its unique buckling spring mechanism, which offers a tactile and sound feedback that is very satisfying. These keyboards are known for their exceptional durability, some examples still functioning perfectly after more than 40 years of use.
I recently acquired a Model M manufactured in the United Kingdom on 18 September 1990, which required a complete restoration. This keyboard features a rare AZERTY French configuration for a British model. Despite its age of over 40 years and its very dirty state, the mechanism seemed intact and the keyboard functional.
The IBM InfoWindow terminals, which allow access to the AS/400 system interface, specifically require this type of keyboard with an RJ11 connector. Standard PS/2 or USB keyboards are not compatible with these terminals. This keyboard is an essential element for being able to use my previously restored IBM AS/400 9401-150:
In this article, I will detail the complete process of disassembly, cleaning, and restoration of this historical keyboard. I will also present some interesting technical aspects discovered during its analysis.
Analyse
The Model M I acquired presents the following characteristics:
- Reference : 1391406
- Date of manufacture : 18 September 1990
- Manufacturing location : United Kingdom
- Layout : AZERTY French
- Connectivity : RJ11 (telephone connector)
- Poids : environ 2,5 kg
- Construction : Plastique ABS et plaque en acier
The particularity of this type of keyboard is its RJ11 connectivity, similar to a telephone connector. This interface was used to connect the keyboard to the IBM InfoWindow terminals for AS/400.
The keyboard was in a very dirty state after years of use and storage. A thick layer of dust, debris, and crass had accumulated between the keys and in the mechanisms. The keys were yellowed and dull, and some had traces of dried liquids. A thorough cleaning was clearly necessary before the keyboard could be used again.
Disassembly and cleaning
The first step of the restoration process is to completely disassemble the keyboard to clean each component. The disassembly is done in several steps:
Removal of keys
The first step is to remove all the keys from the keyboard. For this, I used a specific key extractor that allows them to be removed without damaging them. The Model M keys are particularly resistant but it is still necessary to proceed with caution.
Disassembly of the case
Once the keys are removed, it is necessary to unscrew the 5 screws located under the keyboard to separate the two parts of the case. These screws have a hexagonal head without a slot. The disassembly reveals the internal assembly of the keyboard with its characteristic steel plate.
The ABS plastic case can then be cleaned separately from the electronic components. A soap water cleaning allows to eliminate the dirt accumulated over the years.
A bit of reverse engineering
By examining the keyboard controller card, we can identify several interesting components:
- In
U1, a TISN7406Nintegrated circuit which contains 6 non-inverting buffer inverters in a PDIP-14 package. - In
U2, a STEF6805U3Pmicrocontroller which is an 8-bit microcomputer integrating a processor, a clock, a ROM, a RAM, E/S and a timer on a single chip. It uses the 6800 instruction set. - In
U3, a TISN74LS367ANintegrated circuit which contains 8 3-state buffers. - In
J1, an RJ11 connector for the connection to the AS/400 terminal.
The RJ11 connector
The RJ11 connector is a standard telephone connector with 4 pins. It is used for the connection to the IBM InfoWindow terminal for AS/400.
The wiring diagram of the RJ11 connector is as follows:
| Pin | Signal |
|---|---|
| 1 | +5V |
| 2 | Clock |
| 3 | Data |
| 4 | Ground |
The Clock and Data signals use an inverted logic (active low) via the inverters of the SN7406N. The protocol is similar to that used by IBM AT/XT keyboards but with some differences in the scan codes sent.
The controller card
The keyboard controller card is a “memory” type card with an 8048 integrated circuit and a 2 Ko ROM.