HP-25 sealed keyboard with non responding key

[Sanjeev Visvanatha]

Hello,

I have a HP-25 with the sealed keyboard (no holes behind key domes). The “3” key does not register at all. I read in another thread you could carefully drill a hole at the offending key, and use the wire brush and deoxit method to clean the contacts. However, I did not see if anyone had done this successfully.

For anyone that has performed the drill and clean method : did it work, any issues or concerns?

I worry that the drill debris will just contaminate the button more.

I am not sure the keyboard is original to the unit I have.

[AndiGer]

And if you drill a hole how can you be sure not to interrupt a PCB trace on the other side of the board? Just be lucky?
Andi

[Sanjeev Visvanatha]

This suggestion came from Geoff Quickfall:

https://www.hpmuseum.org/forum/thread-59...l#pid52993

I think it is risky, so wanted to know if anyone had done this procedure and what the results were.

And you are right, it seems the traces on the upper side are not entirely visible, so would be relying on luck at some point.

[John Garza (3665)]

There is, of course, the direct approach.

Slice off the tops of the heat stakes and disassemble the keyboard.
Clean normally as you have full access.
Reassemble and use melted plastic to rebuild the tops of the heat stakes.

And while you're in there, it's a good time to clean/lube the slide switches.

-J

[35/45/55/80/70/65/67/67T/97/97S/91/92/21/22/27/25C/29C/19C/10/
31E/32E/33C/34C/37E/38C/41CX/71B/28S/19BII/12C/15C/33S/35S/32SII/
48GX/50G/Prime/DM42]

[Sanjeev Visvanatha]

Yes that is true. I just don’t trust my skills at putting the keyboard back together.

While cleaning a HP-35 keyboard (beautiful design) using construction paper soaked in Isopropyl, I thought to try something with the HP-25:

I used construction paper to drop Isopropyl around the offending key from the top side. The key now registers! But it’s not entirely reliable. I would say it’s 90% at registering or not producing a double bounce. Since the key is an edge key, I also dropped Isopropyl from the edge of the keyboard layers. I’ll try again a few times before thinking about something more involved.

[Sanjeev Visvanatha]

Update on this. Since the "3" is an edge key, I shaved the domes of the 2 heat stakes surrounding the key. I used a thin plastic, scored to make it rough, and dipped it in IPA. You can slide the thin plastic to where the dome makes contact and remove while gently pressing the key After a few tries, this key registers 100% reliably now. I made no attempt to re-establish the two domes.

This unit is my best looking one, and is now a HP-25E!

[John Garza (3665)]

Great work!

You have a wonderful little machine. The 25 was always one of my favorites.

-J