Replacing a VT100 keyboard connector

Parent Category: How-to's Category: DEC hardware errors, and how to repair them Written by Administrator

Replacing the VT100 keyboard connector

If your VT100 terminal has a defective keyboard female connector, this little picture story is for you!

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The keyboard

The famous VT100 terminal has a keyboard, which is plugged into the logic board over a 6.3mm audio jack.

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The three contacts on the keyboard plug carry Ground, +5V power, and a bidirektional data signal.

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The data signal transports

  1. a clock signal to the keyboard,
  2. control data to the keyboard speaker and the keyboards LEDs,
  3. and scan codes of pressed keys from the keyboard

DEC uses four voltage levels and some analog electronics to pump all this over one single bidirektional wire.

The DEC female keyboard connector

This female keyboard connector on the logic board is constructed pretty cheap and may loose contact to the keyboard male plug. About 1/3 of our VT100s suffer from unreliable keyboards because of this (going "baap-baap" if you touch the desk it is standing on). It has to be replaced with such an standard 6.3mm audio stereo connector then:

This picture is part no. "EBSSV 63" from www.reichelt.de

The original  DEC connector is not replaceable, because it is not a single part at all. It is part of the plastic bezel at the logic board's edge. 

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The contacts are plugged into the bezel housing and are soldered onto the logic board on their own ...
so there is nothing like a "connector", which could be replaced. The whole thing desintegrates if you disassemble it, and makes shortcuts if you try to remount it.

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Replacing procedure

So you have to perform these steps:

1. unscrew the bezel from the logic board

2. unscrew the bezel from the DSUB-25 connector (luckily, the 25pin DSUB connector stays on the logic board)

3. unsolder the two BNC connectors

4. unsolder the three keyboard contacts

 

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5. cut off the housing for the contacts from the bezel, and clean up the damaged plastic you'll leave.

6. widen the keyboard hole in the bezel to 6.3 mm with an appropriate drill.

7. mount the 6.3mm audio connector through this hole.

8. Solder the connector contacts to the logic board again.

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You can see the solder points on the logic board here:
Black = GND, red = Power, white = Signal.

Ready!

As result, the VT100 looks not changed so much.

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