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HP-25 to the rescue and now, rescued!
Posted by Joe Buczek on 28 Aug 2009, 10:57 p.m.
I got my first electronic calculator, a four function TI-2500 Datamath unit with LED display in 1973 when I went off to college in Florida. I think it cost about $200 at the time. A few years went by, and a friend studying ocean engineering was the first HP-35 owner on our campus. I was so impressed by it, but studying computer science, and not having ~$400, I could only lust! Eventually, I earned a few bucks one summer, and in 1975 bought my HP-25 for, I think $200. It seemed to do all that my friend's 35 would do, and it was programmable!
By 1975, I was in the 3rd year of a 4 year degree and was taking a simulation class. The university shared a Univac mainframe with a sister school, and the end of semester crunch time was horrible. Interactive computer response time then was insufferable, and even batch jobs could take hours to get back. So trying to complete a simulation project at that time was nearly impossible... but not if you had an HP-25!!! I sequestered myself in the university library and wrote the queuing equations out for my simulation project, translated them into an HP-25 program, and ran the simulation on paper. I was able to complete my project in about 3 hours one afternoon while other students hoped to get "one run" of their project in before time ran out and projects were due. I was able to redesign my project twice in that time, solving a major problem with it, and got all the data I needed.
Fast forward to 2009. On one or two occasions, since moving to California in the mid 1980's, I took out my HP-25 and tried to get it to turn on. The battery pack was dead, so I put it back in the drawer. Mistake... the next time I looked the batteries had leaked. I took the pack out and, I think discarded it, vowing to open the calculator up and see if I could repair any damage. That project went undone for about 12 years until today.
Today, I opened up my HP-25 and carefully disassembled it. I cleaned the PC board with a sparing amount of flux cleaner and manually scraped the contact fingers connecting the keypad and logic boards and the display. I was amazed to find what looked like actual gold traces on the keypad PC board. Wow!
I put it all back together, and connected it to a bench supply. After a couple of minutes of trying to get a good connection, I flicked the power switch and the display came on!! I hadn't seen that display in about 22 years!! I am totally excited that the calculator still works. I now need to find a dead battery pack and build a replacement, but I now know that the calculator will work when I finally can do this.
So my HP-25 rescued me once and saved my good grade in my simulation class. Now it is my turn to rescue it. What fantastic product quality! They sure don't make them like this any more.
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