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The Memotech MTX Series

MTX Keyboard Replacement

When it was new, the Memotech MTX keyboard was possibly the best keyboard available on any of the home computers of the early 1980s. Thirty years later though, the majority, if not all, MTX keyboards are showing their age, even if they are fully functional, they tend to have sticky keys or unpredictable auto-repeat behaviour - at least mine do. Until now, there has not been a viable option for replacing the MTX keyboard, but, things are about to change!

Dick Janssen (Mrinterface) and Farzad Alizadeh are both working on replacement keyboards for the MTX, they are sharing ideas, but are building their own versions of a new keyboard. Dick has posted a preview of his design in this thread on the Desk Thority website. With Dick's permission, I will be documenting the development of the his design on this page, which will also host the required files such as CAD and 3D printer models.

Jump to latest update

The Memotech MTX system board is installed in a brushed aluminium case, with a full travel, 79 key, keyboard mounted in the upper half of the shell. The keyboard includes separate numeric keypad, 8 function keypad and two blank keys, either side of the spacebar, which, when pressed simultaneously, reset the computer.
The system board is fixed to the bottom of the case and the keyboard PCB is fixed to a steel plate mounted on the underside of the top of the case.

The grey ribbon cable connects the keyboard PCB to the main board by plugging into the "J1" connector above the edge connector on the left hand side of the main board.

Close up of the underside of the top half of Dick's MTX showing the keyboard PCB.

The metal plate for the keyboard is secured to the top half of the case by 5, M3 bolts which are located in the groves that can be seen at either side of the keyboard PCB.

The keyboard removed from the case and the keycaps removed to show the steel mounting plate. Having the keys mounted this way, rather than on just the PCB alone, gives the keyboard extra rigidity.
This is the top side of the keyboard PCB, separated from the steel mounting plate.

Dick's initial thought was to retain the existing steel plate and keyboard PCB. In order to separate the PCB from the steel plate, all of the keys must first be de-soldered. Dick has now decided to design a new PCB and mounting plate - so this level of disassembly is no longer required.

The Memotech key-caps, which you can see are Cherry MX style caps.

The project's goal is to reuse the keycaps to preserve the look of the original MTX keyboard but to replace the keyboard PCB, metal plate and the existing key switches.

The Alps Electric Company produced the original Alps CM key switch used in many computer keyboards. The original switches are no longer made by Alps, but clones are still being manufactured by companies including Matias Corp. of Canada, mainly for use in their own keyboards. 

Matias are making the Matias Switch available to other companies/hobbyists and Dick is using these switches for this project.

A close look at the Memotech key-caps and the Matias switch show the first problem - that of attaching the keycap to the switch.

Dick had previously used FreeCAD, an open source 3D CAD modeller, to design a suitable adapter for Cherry MX key-caps to fit the Matias switch body. The same adapters also fit the Memotech style key-caps.

The adapter was prototyped on a 3D printer.

You can see a YouTube video of the adapter being "printed" here.

Once the design was finalised, the production run was submitted to Shapeways.

A MTX key fitted to a Matias switch using the custom adapter.

This photo illustrates the next problem to be overcome - as shown here, the new keys will be higher than the old ones meaning that they would be raised above the existing key level. This could be overcome by lowering the steel plate further down into the case, but there is very limited clearance within the MTX case and this idea needs further investigation.

Status Update : 09 March 2013

  1. Design Schematic for PCB. 100% DONE
  2. Design PCB. 0% 
  3. Design mounting plate. 0%
  4. Design keycap adapters. 50%
  5. Order parts and assemble it. 0%
Status Update : 12 April 2013

Schematic design in Eagle PCB Design Software

Status Update : 12 April 2013

Alps Switch schematic

Status Update : 12 April 2013

Alps Switch footprint for the PCB

Status Update : 15 April 2013

It is likely that there will be two versions of the keyboard design :

  • Dick will be using Matias (ALPS) switches and.
  • Farzad will be using Cherry MX switches
Status Update : 5 December 2013

As you can see, there has not been any updates to Dick's MTX keyboard replacement project for a while.

Dick's time has been taken up by his ComputerLab - a project to teach kids how to program their own computer games (the website is only available in Dutch).

Dick hopes to revisit the MTX keyboard project in 1Q 2014.

"Welcome to the computer lab!
There are about 50,000 children in Eindhoven who would like to learn and master computer technology through having fun. The computerlab aims to increase the affinity of these children with computers and technology, and provides opportunities for faster learning."

(Quoted from the website, processed with Google Translate, mangled by me)
Status Update : 10 August 2014

Slightly later than planned, Dick is now progressing his keyboard project again. [Although a replacement MTX keyboard is of great interest to us Memotech devotees, Dick's real aims are bigger than just creating a new keyboard.]

Taking his ComputerLab project a little further, Dick has been looking into ways to teach the art of 'making' stuff over the last year and has decided to use the tools provided by 123D, a free suite of design software from Autodesk (of AutoCAD fame).

Dick describes his future plans . . . . . .

"My plan is to set up shop with a 1 day course in 3D modelling and 3D printing, a 1 day course in 2D modelling and CNC milling, and a 1 day course in creating your own electronics PCB together with basic electronics knowledge.

In order for me to be able to teach this, I need to get myself some knowledge about the tools themselves and what a nice project this MTX keyboard is! I need to create the schematic and PCB, I need to create a mounting plate in 2D and have it milled, I also need to create 3D custom keycap adapters with 123D Design. So with this 1 project I'm getting familiar with 3 tools. When the project is done, I'll create tutorial videos about the subject and post them on 040-makelab.nl "

The drivers for using 123D were :-

  1. Free
  2. Multiplatform ( most tools are browser based )
  3. If you get used to using any one tool from the toolset, you can easily transfer to a more elaborate tool like KiCad or Blender since the underlying design principles are the same. So the tools are not as feature rich as other ( free ) tools, but they have the lowest entry level barrier I found on the market today
  4. Sharing and collaborating on designs is very easy.
 
 
Autodesk 123D Free Apps
 
Therefore, the Eagle files have now been imported into 123D Circuits

The current ComputerLab website will be renamed 040-gamelab.nl

The two new websites will go live in September and Dick's plan is to have everything in place by the end of this year.

[ For info, "040" is the phone area code for Eindhoven ]

Status Update : 22 August 2014

Despite its early promise, Dick won't now be using the 123D tools for the PCB and the adapters. [Dick] "tried and found so many problems I could not get it the way I wanted it to. 123D tools are still very good for entry level work, but my work on the keyboard is more difficult than these tools can handle.

So I will be using KiCad for the PCB design and a combination of FreeCad and Blender for the adapter design.

Status Update : 23 August 2014

The 3D model for the redesigned keycap adapter. The middle row adapter is for the Memotech MTX. (The other ones are for Cherry MX to Alps and Alps to Cherry MX).

The model is currently being 3D printed by Shapeways.

Status Update : 09 October 2014

The parts are back form Shapeways, but Dick is struggling to find the time to test them, so has roped in some volunteers to test the results.

   
   
   
   
   

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