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Unshakable Bond with (almost) Unbreakable HP

Posted by Paul J. Brogger on 2 Apr 2000, 9:49 p.m.

My excellent 1st-year math professor, Dr. Matthew Halfant (Hi, Matt!), strongly recommended we students buy HPís when we went out to get our calculators for college. I drove two hours to Portland to buy an HP-21, and fell in love. Other than using it to learn and appreciate RPN, my most vivid HP-21 memory is when the power went out unexpectedly. Deep in the bowels of our lab building, I turned it on, punched in all 8ís and used it for a flashlight to find my way past the oscilloscopes and out of the building.

My senior year, I ordered an HP-29C by mail order Ė my first stored-program digital computer. In a Computability class, I simulated the Universal Turing Machine (indirectly addressing a multi-register "tape") in 98 steps!

I would routinely toss my HP 6 feet away to the hard brick of "red square" to demonstrate its durability, and the TI users would (probably correctly) point out that thatís not how a calculator is used. My bravado was shattered the last time I tried this little stunt when I turned it on and saw to my horror that the display was filled with flickering ghost images and randomly-lighted segments!

Having played some with electronics hardware, I brazenly decided to try & fix it myself. (Kids: do not try this at home!) Iíd already dismantled the thing to see what it was like inside, so that part was easy. Everything looked O.K. superficially, so I took the clear plastic lens off of the LED circuit board, and examined the display chips under a dissecting microscope. Apparently, the inertia of repeated trips to the pavement had caused some of the hair-fine connecting wire loops to collapse onto one another and to the pcb, shorting out some of the display traces. I sharpened a soda straw, heated it over a Bunsen burner (to remove burrs), and (again working under the dissecting scope), carefully picked up each tiny wire loop, restoring their proper shapes and separation. After re-assembly, the display worked perfectly, and I never undertook dramatic demonstrations of HP durability again!

Since the days of school, Iíve had an -11C, a -28S, a -32S and am now inseparably bound to my HP-42S, which I believe represents the very apex of shirt-pocket-portable RPN calculator design and usefulness.

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