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The HP80 Classic that I purchased a year or so ago had a problem turning on, often requiring a gentle tap or two on the top of the calculator. I finally decided to open it up and look for the problem.
The label in the back was in perfect condition and the bottom rubber feet were securely glued in place, leading me to believe the calculator has never been opened.
Inside I found two problems:
The black negative wire had a bad solder joint, showing an open on my ohmmeter when wiggled and the plastic film between the keys and the metal contact strips was positioned a bit high and interfered with the on/off switch. A small area of the film right next to the on/off switch was blackened and contaminated with grease.
I re-soldered the black wire and trimmed a bit off the top of the plastic film. I removed some debris from the interior with an old toothbrush and IPA. After re-assembly, the calculator works perfectly.
Good to know and thanks for sharing. I have one so at least I can be prepared in case it happens to me! Saving this info just in case!
I suspect the bad solder joint was the primary cause of the calculator turning off while being used, but the plastic film interfering with the on/off switch made the slide switch unreliable.
It was surprising how little dirt and debris made it into the calculator - my HP80 was most likely a treasured possession and treated kindly.
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