Silicone grease beneath the sliding switches on classic models

[Miki Mihajlovic]

This weekend I "restored" an old but good looking HP-67. Restored for me as a total ignorant in hands-on electronics means I took it apart, cleaned the keys with alcohol dusted off the PCBs, replaced the gummy wheel and assembled it back together. Then I realized that the sliding switches are a bit harder to push. They do slide but not smooth. Then after the fact I read on this web site that you are not supposed to clean the grease under the sliding switches. My question here is should I dismantle it again and put some silicon grease under those switches. Is it worthwhile? Could the little metal tabs that actually glide on top of the contacts get worn off sooner if there is no grease? My questions can go on and on.

The reason I am hesitant to open it again is the back label already looks not so perfect from lifting the edges to access two middle screws. I am afraid that I will ruin it totally.

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[Randy Sloyer]

You should absoultely grease the metal to metal contacts of a classic with a plastic safe grease. A small bit on the top of the plastic part of the switch helps reduce friction and makes the switch move easier. Be sure to clean all the old crud off first as they collect so much dirt the switches no longer work properly. This is one of the "classic classic" problems.

Just leave the two screws out from underneath the label and it does not matter how many times you open it.

[Miki Mihajlovic]

Thanks Randy, done it. It feels much better now.