Restoring a Compaq Portable

tony duell ard at
Wed Jan 14 13:42:18 CST 2015

> 3) I can't get the keyboard to respond at all.  I tried touching the
> capacitive pads with bare fingers, anti-static bag material, etc.
> Nothing works.  Solution: I don't know.  I suspect the scan driver and/or
> the sense amp chips may be bad.  These are Exar 22-950-3B (sense driver)
> and 22-908-93A (sense amp).  Does anyone here know a decent source of
> these and/or data sheets?

These seem to be custom ICs used in most Keytronics keyboards. Your best
bet is to find another keyboard to raid if you are _sure_ they are the problem.

I have never seen data sheets for them.

Many machines used such keyboards. The TRS-80 Model 2 (TechRef available
from did, there is a schematic of the keyboard in said manual,
but with no real data on the ICs. The driver takes in a 4 bit value (to select a 
'column' and a strobe pulse, the sense amplifier outputs 8 bits for the selected
rows. Given the TRS-80 M2 diagram it should be possible to see if the 
column select value and strobe are doing anything (if not, then the keyboard 
microcontroller isn't running, I guess), if there is any activity on the column
outputs, and if there is any activity on the sense amplifier outputs when you
simulate a keypress.


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