Key Contact Cleaner

[teenix]

Hi all,

This may be of use to anyone who needs to clean key contacts.

I was fiddling with a HP-67 someone sent to me to try to get going again, but it looks like an ACT failure as the chip gets warm, probably battery-less charging, and although I can see data on the IA bus it seems to be not of any use.

I tried one of my replacement CPU boards which brought it back to life, but hardly any of the keys worked and some gave false key codes to the CPU. After some cleaning they still wouldn't work so I guess the corrosion was a bit worse that expected.

I made a tool as shown in attached image. It was made out of a lid of one of those disposable plastic containers that you can buy in packs for a dollar or so.

I cut out a strip about 5mm wide and scratched a cross hatch pattern one both sides of a small area with a scriber (any sharp item will do). This is easy to do as the plastic is quite soft and this provides a soft but rough double sided cleaning surface.

The plastic is stiff enough to be placed between the metal contact bubble and the keyboard. I used isopropyl alcohol as the cleaner and then the 'tool' is moved back and forward with some finger pressure pushing down on the metal bubble.

After 35 keys done, the keyboard was fixed :-)

Deoxit might be better but I didn't have any.

cheers

Tony

[Maximilian Hohmann]

Hi!

(01-16-2021 04:53 AM)teenix Wrote:  Deoxit might be better but I didn't have any.

I will certainly try something like your tool very soon. Not for a calculator but because I just got a new (new for me, but pre-owned in reality) home-cinema amplifier whose remote control has some non-working keys.

In my experience just cleaning the keys can bring back to life many devices but usually not for long. Without the protecting substances contained in contact cleaners like Deoxit the keys will oxidise even faster than before.

Regards
Max

[Dave Britten]

I've done exactly the same thing, but with strips cut from index cards and then slightly moistened with alcohol. Each strip is only good for cleaning maybe one row of keys, but the roughness of the paper works wonders for scraping out contaminants, and using multiple strips to clean the whole keyboard helps ensure you aren't just dragging the same dirt through later keys. My 65, 45, and 80 keyboards are like new after doing this, with no bounce whatsoever. It's a shame TI didn't build their keyboards in such a way that they could be cleaned like this.

[mfleming]

Can this approach be used on a 71B keyboard? Some of the keys on the bottom row require a firmer press. I don't even want to open the case unless I know I can do something useful!

~Mark