[Coco] CoCo 64K (26-3126) Keyboard Issues Follow-up

[Joel Rees]

2017/12/11 3:46 "Arthur Flexser" <flexser at fiu.edu>:
>
> It does sound like a spill is the most likely explanation, given the
> further information you describe.  With the keyboard unplugged, you could
> try to verify with a meter that some lines are shorted to others, which
> would at least definitely pin the problem down to the keyboard itself.
>
> At least some models of keyboard are held together with a whole bunch of
> tiny screws that must be removed.  Tedious but straightforward.

FWIW, I have memories of opening up at least a couple of coco keyboards,
just to get a look at the keyboard physics. If you can put the screws
somewhere they won't be blown away in the wind or swept away by your
sleeves, etc., and if you have use of both hands and a little patience, it
shouldn't be hard. Just plan on being able to set it aside overnight in
case it takes longr than you expect.

If you find stuff in there that is still liquid or sticky as you open it,
be really careful to avoid getting more of it on the keypad contacts.
That'll corrode the conductive/resistive surface and make it so the key
won't read at all.

Use a wet Q-tip to clean between the contact pads.

Do not use soap, alcohol, etc., only water.

On the other hand, avoid scrubbing.

Especially, do not scrub the pads or the contacts pads on the underside of
the keys. If the contact areas have liquid or sticky stuff on them, wipe
very gently, just until things quit sticking. When the conductive/resistive
surface gets spoiled or rubbed away, that's when you start having to be
really creative. (I can offer some suggestions, but we prefer not to go
there.)

> Art
>
> On Sun, Dec 10, 2017 at 12:58 PM, Christopher <piperfox74 at gmail.com>
wrote:
>
> > Folks,
> >
> > Thanks for the replies.
> >
> > A quick follow-up:
> >
> > 1) No joysticks are plugged in.
> > 2) I disconnected the keyboard ribbon cable, checked continuity across
each
> > conductor, seems fine. Unplugged and replugged in the keyboard several
> > times in case there's oxidation. No effect.
> > 3) It doesn't look like the keyboard's ever seen a spill. It's
immaculate.
> > Admittedly, I haven't taken it apart. I'd consider doing that if I had
some
> > instructions.
> > 4) The PIA in this unit is a 6822. I had a spare 6821 and swapped it in.
> > Saw a similar issue. (I've read the 6821 isn't necessarily a direct swap
> > for the 6822?)
> > 5) For the most part, the issues seem to occur across keys mapped to
pins
> > 9, 10 and 11 on the matrix, e.g. pressing 1 or 2 gives "12" on screen,
> > pressing Break clears the screen and inserts a line feed, etc. I'd say
the
> > issues definitely seem localized to keys mapped across pins 6 through
11.
> >
> > I don't have another PIA to test with, so it looks like I may be out of
> > luck on this unit. If it turns out this is not a quick fix or is
otherwise
> > out of my skillset or available parts, I'd be willing to part with it
for
> > the cost of shipping if anyone is interested.
> >
> > Thanks,
> >
> > Christopher
> >
> > --
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> > Coco at maltedmedia.com
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> >
>
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