Question about older keyboards.

From: Ernest <ernestls_at_attbi.com>
Date: Mon Dec 10 21:49:11 2001

> -----Original Message-----
> From: owner-classiccmp_at_classiccmp.org
> [mailto:owner-classiccmp_at_classiccmp.org]On Behalf Of Tony Duell
> Sent: Monday, December 10, 2001 4:17 PM
> To: classiccmp_at_classiccmp.org
> Subject: Re: Question about older keyboards.
>
> >
> > I have an old keyboard with those soldered on keycap
> assemblies. One of the
>
> A general point : Please post the make/model and any other information
> that will identify the unit. Somebody may know the exact device you are
> talking about, and/or have a service manual for it.

I considered this but I don't think that anyone here knows anything about
this keyboard.
It looks like a very simple homemade job -hand soldered anyway. It isn't
wire-wrapped but
close to it.

> > key mechanisms broke off and now I'm receiving random characters on the
> > screen. The missing key is the #3 key. Could the fact that this
> mechanism is
> > missing cause this kind of problem, or would the computer see
> that missing
>
> It depends :

> 2) If it's totally missing, and only has 2 connections, then it's a
> switch. Having it missing should cause no problems, it will just appear
> not to ever be pressed

This is the case on this keyboard. The board has one TI SN74159N chip that
all the keys connect to at one place or another.
It's discription is: 4-LINE TO 16-LINE DECODERS/DEMULTIPLEXERS WITH OPEN
COLLECTOR OUTPUTS. Looking at the keyboard, aside from the missing key
mechanism, the board "looks" OK. It's even dust free. There is one thing
that's interesting but I'm not sure if it's a bad thing or not. There is
what looks like an intentional solder bridge between the 6-7 pins (if the
notch faces away from you, it's on the right side in the middle.)

So, if the keyboard seems to be OK, where would I next look for the cause of
a few random characters being generated on startup? Any tips here will help.

Thanks.

E.

>
Received on Mon Dec 10 2001 - 21:49:11 GMT