7 Oct
2026
7 Oct
'26
6:17 a.m.
From my personal experience with such type of contacts I have in my
ADM-3A I favor DeoxIT. They make a great syringe version of their
product. The version for pots works the best for me as it adds some
lubrication to the contacts without compromising the conductivity. It
will also be the least aggressive mechanical cleaning as the product
does the work for you as you work the key pressing. Hope this helps.
On 10/6/26 3:43 PM, Charles Morris via cctalk wrote:
It does get better with repetition, but never goes
completely away.
The contacts are almost dry-circuit (4.7K pullup + one TTL input) so
will only clean up mechanically.
I'll try pulling a couple of key caps and see if I can carefully clean
the contacts.
On 10/6/26 14:24, Fred Cisin via cctalk wrote:
> Does it get better, or WORSE, with extended use?
>
> Sometimes, oxidized or dirty contacts clean themselves a little with more
> use, and are especially bad with non-use.
>
>
> 40? years ago, I was handed a "dead" TRS80 keyboard. After repeatedly
> beating on one key, it gave a hit! And, would work a small part of the
> time. I tried with others, and determined that extended excessively heavy
> use seemed to re-enable keys, at least sporadially!
>
> So, I dug out a Rochester Dynatyper Keyboard Actuator. It was like the
> KGS80, a box of solenoids intended to be set on top of a typewriter
> keyboard to turn a typewriter into a cheap printer (back when "cheap"
> computer printers were a thousand dollars). Those would "print"
> relatively reliably at about 8 characters per second. There also existed
> the Escon (Walnut Creek) Model E-P, which was the same idea but Selectric
> specific, and mounted inside the Selectric, and pulled the keys down; that
> could almost handle the 14.8 characters per second maximum of Selectrics.
>
> I set the Rochester on top of the keyboard, and sent enormous text files
> to "print". After a while some of the keys were working! By the next
> morning, they all worked!
>
>
> Before trying that, consider that if the problem is mechanical, it might
> help those keys, or it might wear them out, and finish killing them.
>
> --
> Grumpy Ol' Fred cisin(a)xenosoft.com
>
>
> On Tue, 6 Oct 2026, Charles Morris via cctalk wrote:
>
>> I'll check the p/s, but since everything else works correctly, I suspect
>> dirty key contacts and a poor debouncing circuit.
>> Pressing (for example) the "2" key, sometimes it outputs
"22",
>> sometimes "2v"... the debounce circuit should take care of the first,
>> and the second has falsely set bits (0x32 vs 0x76).
>> Some of the other keys have either or both errors too - will have to log
>> the errors associated with each key and see if I can find it in the logic.