HP67 : repairing a keyboard

[albertofenini]

We wanted to share how we repaired a keyboard a couple of weekends ago, it may be useful for someone else.
We were restoring our HP67 and while cleaning the unit, we discovered that the last (first) row
at the bottom of the keyboard was broken.
The metal bridges were so stressed and thin that they were breaking apart.
Using an exacto knife and been careful enough not to break it we carved a line from an old HP45.
We removed the old, cleaned with the help of a a pen rubber and we positioned the new strip.
Having cleaned with some sand paper (1000 grit) the small holes left from cutting the strip off
the 45, we were able to do some soldering to help keep in place the new strip.
It worked very well, and now the keys have the original click and feel like new.

               

[burkhard]

(02-16-2019 09:12 PM)albertofenini Wrote:  We wanted to share how we repaired a keyboard a couple of weekends ago, it may be useful for someone else.
We were restoring our HP67 and while cleaning the unit, we discovered that the last (first) row
at the bottom of the keyboard was broken.
The metal bridges were so stressed and thin that they were breaking apart.
Using an exacto knife and been careful enough not to break it we carved a line from an old HP45.
We removed the old, cleaned with the help of a a pen rubber and we positioned the new strip.
Having cleaned with some sand paper (1000 grit) the small holes left from cutting the strip off
the 45, we were able to do some soldering to help keep in place the new strip.
It worked very well, and now the keys have the original click and feel like new.

Great pictures!
What sort of gunk/corrosion is all over the original key metal? It looks like somebody spilled a Coca-Cola on there or something!

A question on using the HP45 metal "bridges" in the 67. In the 35 and 45 units I have, the key feel is quite a bit lower force and less "clicky" than in my 55, 65 & 67 units. Somehow I was under the impression that the earlier calculators had different metallurgy (maybe with gold plating?) in the keys and that it was changed on later models to save cost, which it did, but there was also a different feel. I'm a bit fuzzy & unsure on my recollection, though.

Do you find that your repaired bottom row now feels like the others?

thanks!

[albertofenini]

As you can see is a very old keyboard, on the contrary the HP45 we used was well kept.
The other HP67 keys were less strong than normal keyboards while the HP45 a little stronger.
I think it was a good compromise, and on the other side the only available option.
The line we replaced was physically broken, so it was a no go situation, the rest of the
unit was worth the work done and the feeling is very very close to all of our units.
Given that the upper part of the keyboard had almost no corrosion, I also think that someone
had spilled something and not taken too much care in cleaning.
This calculators have a thin plastic film between the keys and the keyboard, which can prevent
liquids to pass thru, but only in small amount.

[TRS80]

Thank you, this does indeed help, for I have an HP67 that I acquired that has crumbling key metal due to corrosion. I may try a similar fix. I had thought of soldering the key metal as the original is spot-welded.
-trs80