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

[Arthur Flexser]

Now that I think about it, the problem of extra, as opposed to missed, keys
sounds like lines are being shorted together, so corrosion is unlikely to
play a role.  Could the ribbon connector be so loose in its socket that
there is sideplay that would allow adjacent pins to get shorted together?
Still sounds like something an inserted strip might well eliminate.  You
should check with an ohmmeter that no lines are shorted together when the
keyboard is unplugged, to eliminate the possibility of shorting within the
keyboard as from a spilled drink and confirm that the problem lies with the
socket connection.

Art

On Sun, Dec 10, 2017 at 8:26 PM, Arthur Flexser <flexser at fiu.edu> wrote:

> The thin strip of plastic idea sounds like it might do the trick.  Also,
> see if there is any corrosion at the points where the ribbon cable makes
> contact with the socket.
>
> Art
>
> On Sun, Dec 10, 2017 at 7:28 PM, Christopher <piperfox74 at gmail.com> wrote:
>
>> Following up again.
>>
>> This keyboard has no screws. It looks like the PCB is heat-staked to the
>> plastic surround. It’s the low-profile “melted keyboard” variant.
>>
>> I think I’ve actually narrowed down the issue to a weak connection
>> between the keyboard ribbon cable and its connector on the motherboard.
>> Manipulation of the ribbon cable while in the socket results in missed
>> keys, extra keys, etc. Is there any way to reinforce this connection? I was
>> thinking of adding a thin strip of cardboard or plastic to try to improve
>> contact between the ribbon cable traces and the connector.
>>
>> Thanks again to all who’ve responded with tips.
>>
>> Christopher
>>
>>
>> > On Dec 10, 2017, at 19:02, Joel Rees <joel.rees at gmail.com> wrote:
>> >
>> > 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
>> >>>
>> >>> --
>> >>> Coco mailing list
>> >>> Coco at maltedmedia.com
>> >>> https://pairlist5.pair.net/mailman/listinfo/coco
>> >>>
>> >>
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>> >
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>>
>>
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>
>