Wednesday, March 26, 2014

Repairing a HP41CX

Our cat is only trained on algebraic entry system. I don't otherwise know how to explain why he threw my vintage HP 41CX on the floor. Doesn't he look frustrated and confused by RPN entry? Unfortunately after a dive from the table onto the floor, my HP41CX wouldn't boot.

This wasn't the first repair I've done to it. I originally rescued it from my Dad who was going to contribute it to his township's unneeded electronics drive.

VINTAGE CALCULATOR GOING IN THE GARBAGE? Sweet Baby Jesus. I love old calculators! Probably because once upon a time I used to work for HP in the calculator lab. This shabby treatment of a highly prized relic would not do, even though it was dead.

After cleaning the corroded battery compartment from long drained and oozing batteries, the foil touching the battery tips was eaten through. I inserted a strategic bit of aluminum foil to bridge the worn down battery contacts fired up to life!

That was about a year ago, and she was a trusty old friend until the cat incident. My poor old HP41CX has been sitting around again for a while, dead to the world and patiently waiting for me to get up the nerve to crack it open and see what was wrong. In light of my recent success repairing a sea-soaked Z10, I decided to give it a go.

First, I looked at the HP Calculator Museum on disassembly and repair tips. I popped open the battery compartment, removed the rubber feet, unscrewed the back, and pulled it apart.

The thing I was most worried about was broken screw posts, which seems to be a common occurrence with this model. However, everything looked in order--no broken posts. All the other components were solidly attached. There was still a lot of corrosion on the interconnect left over from my first cleaning. I cleaned that thoroughly with rubbing alcohol and a Q-tip, and then slightly squeezed the interconnect flex strip. That compression was to bow the contact strip outwards more, allowing it to more solidly touch when I reassembled the unit.

I put it back together, and it worked first time, another TINY VICTORY!

Maybe I should start an electronics repair company! Okay, maybe not. But I'm still quite happy that I've saved two of my devices from the landfill. Just so it won't happen again, I'll start teaching the cat how to use RPN. Wish me luck.

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