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Rockwell 475P/D

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Here's another desktop calculator that doesn't really belong to my collection, were it not for the fact that its repair makes an interesting war story.

When this calculator arrived from the UK, it was slightly damaged: the screwposts of the printer assembly were ripped out of their plastic posts, and the printer assembly moved about. When I powered it up, nothing appeared on the calculator's display, and the printer motor was spinning continuously.

Naturally, I assumed that something might be wrong with the printer, so I disconnected it. This didn't solve the problem: the display remained blank and the calculator showed no signs of life. I was able to confirm that all voltages were correct and present, so it was not some obvious problem, like a bad power supply.

In an e-mail, Mike Sebastian mentioned that he has seen calculators in the past with faulty printer assemblies whose display never came to life. So I decided to re-examine the printer, but still saw no damage or contamination that could cause any misbehavior. It was then that I noticed, however, that a capacitor near the printer connector was physically damaged, no doubt by the printer assembly itself during transport. After I replaced the capacitor, the calculator instantly came to life, and it is working perfectly.

So why would I want to get an old desktop calculator all the way from the UK anyway? Simple: it's a programmable calculator. Not very programmable, mind you: only 16 program steps, not a heck of a lot for a four-function machine. (I suppose back in the good ole' days, it was still useful to program a tax calculation or something.)

Using 10 of those 16 steps, it is possible to teach this calculator to do square roots. The following little program must be run repeatedly, until the result on the display no longer changes. The number the square root of which you wish to compute must first be placed in the calculator's memory:

01   +
02   /
03   MR
04   EXC
05   =
06   +
07   T
08   /
09   2
10   =