HP-41 top mtg. screws

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HP-41 top mtg. screws

Postby John B. » Tue Aug 24, 2021 10:03 pm

The top pair of screw lands had broken loose causing loss of pressure-sensitive interconnections / no powering on. Disassembling and cleaning all the connections, upon reassembly the HP-41 'wanted' to power-up but wouldn't work reliably. A plastic zip-tie was cinched around the reassembled HP-41 'sandwich' just below the power switch which helped. A snug piece of stainless steel wire in place of the zip-tie was better, yet 'iffy'.

While at the dentist, a kindly hygienist shot a pair of X-Rays where the top pair of HP-41 screws should be. Turns out there's nothing / no circuitry or component internally preventing drilling a pair of all-the-way-through screw holes!

With extreme care, a 3/32" twist drill was used to drill through the entire HP-41 'sandwich' from the back side, using a drill press to ensure drilling perpendicular to the back face in the very center of the screw holes (exposed under the peeled off pair of top rubber pads). The drill bit egressed on the front side of the HP-41 bisecting the gold band above the summation and LN keys. A pair of stainless M2 x 32mm machine screws (cut to exact length with a jeweler's saw) were fed through from the back side. A pair of M2 hex nuts catch the screw threads on the top/front of the HP-41. (A pair of tiny semicircular notches, counter bored into the thicker black plastic material 'north' towards the display, make room for the tiny hex nuts.)

These two screws have perfectly restored operation - clamping the HP-41 'sandwich' exactly as the original screws intended.
John B.
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Re: HP-41 top mtg. screws

Postby Garth » Wed Aug 25, 2021 4:20 am

Good story. Designers seem deathly afraid of letting any screws show; but I don't particularly mind, especially if it gives a feeling of confidence that the product is built solidly. I took apart a lot of military surplus electronics that was given to me when I was a poor paper boy in the 1970's, to get all sorts of parts I would never be able to afford. I'm not sure I ever used a significant percentage of them, but they sure got my imagination going as to the possibilities for my many projects. Military equipment was not designed to appeal to a market like home stereos, calculators, cars, etc. though, and it had screws showing all over the front panels. It seemed pretty indestructible too, in spite of using tubes, and seemed like you could drop it off a tall building and it would still work.
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