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Full Version: HP 67 cleaning: which silicone grease for the switches?
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I have acquired a working HP 67 at a reasonable cost (I have the feeling that this very sentence is the most important one of this post Tongue)
However, three of the top keys don't work (B, C, E). Furthermore, when I switch on the calculator, sometimes there are weird numbers in the display, instead of 0.00.
I've opened the case, following various instructions I have found on the web (thank you to all those who have posted these explanations!)
The inside was very dirty. I cleaned the space underneath the metal bridges by inserting and sliding paper strips, and I had the confirmation that the top row was dirty. I hope this will solve the problem for the keys.

Now, I have a question about the ON/OFF and PRGM/RUN switches. There was a strange dark paste above the contacts, and I preferred to remove it.
I have read that silicone grease must be applied on these contacts. I have silicone grease for taps/faucets. Is it suitable for that?

Also, I wonder how it can work. My understanding is that grease is an insulating material. How contact can happen if there is insulating grease?
Concerning the silicone grease: that's exactly the thing I use. And it works great.
Have no idea why it works but it does.
On car batteries people also use pole grease ...
A dielectric grease is preferred, like Lubriplate DS-ES.
(06-22-2019 03:44 PM)Dave Frederickson Wrote: [ -> ]A dielectric grease is preferred, like Lubriplate DS-ES.
Thank you. So, it's a lithium grease.
As I was eager to see the result of my cleaning, I used plumbing silicone grease. I can confirm that the calculator now works perfectly!
Even one mushy key has recovered its firmness, probably because a particle of dirt was encrusted on one side of the key, preventing it to press the center of the "dome".
I am more than happy!
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