Texas TI-59: A tale in pictures

[jebem]

(11-22-2014 07:29 PM)Marcus von Cube Wrote:  

(11-22-2014 06:19 PM)jebem Wrote:  IMHO the bouncing issue with these keyboards are related to the fact that some of the dome's crimping connections are getting lose with the usage.

I'd be glad to see a reliable fix for the issue.

When I have the time, I will try to restore my Texas TI-58 that is missing his original keyboard donated to the 59.
Now I have a dismantled 59 keyboard to play with.

Looking to the keyboard white plastic frame, we can see a number of small holes in front of the crimping/welding points. I think Texas made a less than perfect job when welding these joints, resulting in a lot of failing keyboards.

In my case, these mechanical/electrical joints were broken in several positions, and I believe this was causing both bouncing and missing keys as well.
Pressing a key can either cause multiple contacts spaced in time in a way that the debouncing software routine can't handle, or a total failure to register.

After reading so much reports from others here and there, I have noted that some people can fix some of these keyboard issues by just manipulating the original foam that sits between the plastic keys and the domes.
This makes sense to me, as the foam makes some pressure to the domes forcing them to make a better contact with the keyboard frame wires.
A thicker foam should give better results as well. I did it on one TI-57 some time ago with some success.

To test my hypothesis, I was thinking on soldering all the dome's connection points where originally it were crimped/welded at factory.
To do this, the plan is to lay down and solder one row of domes at a time.

Then, apply some sort of self adhesive plastic film, similar to the original one. I have yet to find the appropriate one for this application, though.