PDA

View Full Version : Bringing up a Vector Graphic Mindless Terminal



MarsMan2020
August 16th, 2015, 12:37 AM
(previous thread on my MZ was here - Bringing up a Vector Graphic MZ (http://www.vintage-computer.com/vcforum/showthread.php?40587-Bringing-Up-a-Vector-Graphic-MZ))

I finally got my hands on a Vector Mindless Terminal to go with my MZ. Sweet!

However, the "foam and foil (http://deskthority.net/wiki/Key_Tronic_foam_and_foil)" in the Keytronic keyboard had turned into....foil and "dust that used to be foam". Not so sweet.

So, I fired up my web browser, took some measurements of the existing parts, popped over to www.mcmaster.com (my favorite industrial supply place), and ordered some self-adhesive plastic, self adhesive foam, aluminized mylar film, and a 7/16" punch:

25883

25882

25881

25880

25879

(I'll post the parts list for my fix after I've had a chance to use it for a month or two, there is one aspect of it that I am a little concerned about the durability of. Most of the fixes I could find online involved individually gluing the sandwiches back together - I went with the solution of making an entire new sandwich which I think is a lot less time consuming.)

deramp5113
August 16th, 2015, 02:02 PM
Looks like a good idea - keep us posted!

Mike

tkc8800
August 16th, 2015, 03:55 PM
Resulting parts look very good. The Compaq portable uses these key pads. I made some quick-fix pads a while back but I need to make some better pads like yours.

MarsMan2020
August 16th, 2015, 09:53 PM
I used from mcmaster.com:
-.007" self adhesive UHMW polyethylene plastic
-3/16" (0.187") self adhesive polyurethane foam
-.002" aluminized mylar (aluminized & conductive on one side only, non-conductive on the other side)

Some notes on each layer, working down the stack:
-I ended up using 2 layers of the UHMW plastic to make it more stiff, and it still ended up being flimsier than the clear discs used on the original parts. I had to use a plastic pick tool to careful tuck this new plastic under the "grabbers" on each key, at which point it doesn't seem like it is going to come out again.
-The adhesive between the plastic and the foam is the thing I am worried about. A couple of them started to separate during the "tucking" described above. I'll see if this holds up for a month or two.
-For the foam, I tried another closed-cell foam that was stiffer, but the impact from the keystrokes dislodged them from the small "grabbers". Conclusion - using open celled foam is important.
-The adhesive between the foam and the thin aluminized mylar seems perfect. I don't see this coming apart at all. It may have been a better quality adhesive.
-The aluminized mylar wants to have the *non-conductive* surface facing the pads on the PCB - checked against the original pieces that I removed (makes sense, the switches are capacitive not conductive).

If I were going to do this again I would get a more rigid plastic similar to the original clear discs (measured .007" with calipers) and glue that to the same type of foam using something like 3M Super 77 adhesive. Then I'd stick the mylar to the self-adhesive foam, wait a bit for the Super 77 adhesive to cure, and punch out the "sandwich" all at once just like I did here.

I think overall this was a big improvement over the more time consuming methods involving trying to clean up and reuse the original plastic discs and mylar discs.