HP-67 cleaning pcb keyboard contacts

[coitboy2000]

Hi All,

I am trying to revive an old HP-67 and, thanks to Tony (aka Teenix) have a new replacement pcb (and a working card reader thanks Tony!!) as the old one had died. The calculator has had a tough life and some corrosion exists on the keyboard/pcb/domes. The story began in this post:

https://www.hpmuseum.org/forum/thread-15727.html

Anyway, the calculator has come back to life but the results on the leds's is somewhat random when I press certain keys. The keyboard is the likely culprit (shorts etc) and even though I have scrubbed it with alcohol & a toothbrush and also ran some paper under each contact the problem still exists. Is there another way to clean the keyboard i.e. could I desolder it from the main board and immerse in vinegar or something else ? Just looking for some ideas.

Cheers

Richard

[[kby]]

I think you might need to clarify your question: what exactly are you trying to detach from what? It seems as if you’ve been inside if you have sanded under the buckle springs, but your question regarding desoldering the main board doesn’t make sense as the “main board” description normally would refer to (e a synonym for) the replacement pcb you got from Tony, and it is not soldered to the board with the keyboard buckle springs; it only is attached with the infamous gold fingers. The springs are (I’m guessing) spot-welded to the keyboard pcb so I don’t think nom-destructively detaching and reattaching the springs would be feasible. I would mostly worry about moisture getting stuck in the LEDs (under the bubble lenses).-kby

[teenix]

(02-24-2021 11:37 PM)[kby] Wrote:  I think you might need to clarify your question: what exactly are you trying to detach from what? It seems as if you’ve been inside if you have sanded under the buckle springs, but your question regarding desoldering the main board doesn’t make sense as the “main board” description normally would refer to (e a synonym for) the replacement pcb you got from Tony, and it is not soldered to the board with the keyboard buckle springs; it only is attached with the infamous gold fingers. The springs are (I’m guessing) spot-welded to the keyboard pcb so I don’t think nom-destructively detaching and reattaching the springs would be feasible. I would mostly worry about moisture getting stuck in the LEDs (under the bubble lenses).-kby

Some background...

I offered to have a look at the faulty 67.

The calculator looked like it had a bad battery leak some time ago and has left its mark throughout the innards, as well, a few signs of 3rd party repair, and the original CPU board did not work.

I stripped it down and cleaned it all, added a new CPU replacement and refurbished the card reader and wiring. It now works but this was the keyboard that I cleaned using the soft "cross-hatched" plastic strips I made up. The keyboard did work ok for awhile so I suspect surface corrosion came back. The tension on the key contact strips has also waned over the years resulting in a less than positive feel, but I don't think they are replaceable - not easily anyway.

It was my suggestion to post a query here as my only thought was De-Oxit as a hope to repair it as it may leave some protection on the key contacts ?? I haven't used this before and it is expensive here, so I thought some Forum feedback may have helped.

cheers

Tony

[[kby]]

Ah…the dangers of getting third party information. If the question is really about demo it, I’d try your plastic strips with the G5 variant. I think I’ve tried it alone on -65 keyboard w/o much luck, but it might work better with the plastic strip or other mild abrasive technique.-kby

[coitboy2000]

(02-25-2021 11:14 PM)[kby] Wrote:  Ah…the dangers of getting third party information. If the question is really about demo it, I’d try your plastic strips with the G5 variant. I think I’ve tried it alone on -65 keyboard w/o much luck, but it might work better with the plastic strip or other mild abrasive technique.-kby

Third party ? Anyway, thanks. By keyboard I meant the keynoard pcb. The desoldering is just the two wires for the power. Sorry I wasnt more clear. I am going to try the vinegar.

Richard

[coitboy2000]

The vinegar combined with a toothbrush did the trick.