Triton released 1978 - SD Keyboard

The Keyboard on My Triton came from an old Computer Automation INC Syfa systems VDU 1. It has a nice action because of its hall effect key switches. the Keyboard is made by Micro Switch there in no information on this Keyboard model that I can find details as follows:-

Micro Switch CAT LIST 84SD12-2

SER NO. 001389

Part No on PCB SD-16139

84SD12-3 SD-Keyboard-History

This Keyboard is not working, it has power of +5v and -12v, some of the data output lines go to -12v when you press some keys. The strobe line is sitting at some strange level of +2.1v.

Read about the Keyboard Restoration project here

The Key switch encoder chip is an SW20457K (40 pin) by the logo made by AMI no information on this device.

There is information on Micro Switch SD Series on the Telcontar.net web site.

There is also more information here deskthority.net

From the date code photo below 77/39 suggests it was manufactured in 1977.

Micro Switch Keyboard 84SD12-2

The Keyboard uses a number of Hall effect switches, lots for information on this page Micro Switch and Honeywell. This keyboard has 84 key positions on the PCB but two are not installed at key position 1 an 17. A map of the key positions can be found on the next page.

A Number of different switch types are used as follows:-

5B3A Shift Lock key

4B3A Shift (left and right) CTL RPT BREAK

4A1B Large ENTER BACKSPACE CANCEL numeric keypad

6B1D Extra support for above keys (two on enter key)

4B3B All other keys

On this Keyboard a number of these keys switches are dead either they only produce a single output or no output, with one holding it output low all the time regardless of switch position.

In the progress of finding parts to repair this keyboard I found DSM Components they have the Tesla MH3SD2, proximity sensor with Hall probe and MH3ST2, Schmitt trigger they have been very helpful good service and the parts turned up on time as expected.

The data sheet is for sensors here MH3SD2 MH3SS2 some more information on the telcontar.net website Tesla hall sensors

The circuit diagram is on this link

Micro Switch SD Keyboard 84SD12-2

Output table here Which shows out put codes for its 84 keys in key number order including shift and control.

The dual-output switches are set up for two of 13 coding. the output pins on the switch are numbered pins 2 and pin 3 they go to inputs on the encoder IC, the table lists these pin numbers. This is not a matrix scan keyboard. When a key is pressed the hall sensors sends out 2 pulses (Pin 2,3) the encoder will receive these on 2 of its 13 input pins and encode this to the output code. The use of pulse output avoids clashes when two keys are held at once.

Computer Automation Syfa system VDU 1

Micro Switch keyboard encoder SW20457K

Micro Switch PCB SD-16139

Micro Switch Hall sensors IC die

Micro Switch sink pulse (B) Hall sensors

Enter key module and sensor

Close up of hall effect sensor including the die on both sides and the ceramic substrate

The keyboard has be modified to include a DM96L02 Dual Retriggerable Resettable Monostable Multivibrator to stretch the strobe pulse for use with the Transam Triton intel 8080 based computer. This chip is in the photo on the right in the blue IC holder there is also an extra three resistors and a capacitor placed near the blue IC holder.