Tandy TRS-80 Model 4 Replacement Keyboard
Like many owners of the Tandy TRS-80 Model 4, I experienced failing keyboard contacts. I quickly learned that servicing the stock switches is difficult, time consuming, and no fun.
I designed a replacement keyboard with the help of www.Keyboard-Layout-Editor.com, Plate & Case Builder, and EasyEDA. This replacement keyboard is meant to use Cherry/Gateron MX switch footprints and match the Row/Column wiring of the original keyboard matrix as detailed on the maintenance manual schematic. It's designed so that a typical 20 Pin IDC cable connection can connect to the keyboard, and the other end to the motherboard itself. It also adds footprint support for extra keys that are supported in the ROM but were not shown in the schematic keyboard matrix. Extensive support holes are added for use as a generic retro keyboard by enthusiasts. If +5V DC is supplied via Pin 17(*** See note in project files) and an optional 330 Ohm resistor installed, a Power LED can be installed to coincide with the footprint of the RESET switch for compatible MX key switches.
The keyboard is not compatible with the original keyboard plate, but a new compatible plate has been designed courtesy of user alnwlsn on Discord. If mounted above the original plate, the original bezel will not be compatible. When used with a compatible plate, the original bezel will be compatible if the ribbon cable header is installed on the underside of the PCB using the provided footprint and the extra three keys to the right of the numeric keypad are omitted.
Project files can be found at this link.
To sign up or express interest in a future production run, fill out this form.
Video on how to build and install the keyboard:
Picture of the completed version 3 keyboard installed in the Model 4 :