HP-65, 45, 80 On/Off Switch Problems

[teenix]

The switch should feel fairly tight when sliding OFF - ON or WPGM / RUN and with a higher resistance felt in between as the switch moves across a plastic hump which holds the switch either left or right.

What has most likely happened is the original switch lubricant has deteriorated over the years and is causing problems. It usually ends up a dark brown color and has a thick waxy consistency.

The problem may also be that due to lack of lubricant over the years, the switch contacts have eroded so much that a only very poor connection is being made and cleaning won't do. It is also possible that if the switch feels sloppy to use, the spring contact may have lost some tension and might require some small mechanical adjusting to make it rub harder against the circuit board contacts.

In my opinion then, and I know you really don't want to, the best way is to open up the calculators and give the switch contacts a good clean, both the actual contact and the circuit board pads which it rubs on. Isopropyl alcohol will do. Applying some good quality contact lubricant will keep them working for a long time. If you don't want to spend money, then a "tiny" dab of petroleum jelly.

Contact cleaner may dissolve some of the gunk, but it still resides inside the calculator and may end up elsewhere like under the keyboard contacts.

cheers

Tony