Calculator repair fun

Charles Morris charlesmorris800 at
Sun Jun 7 20:43:13 CDT 2009

This is a perfect example of why I never throw anything away...

a couple of months ago I found a nice Craig (Bowmar) 8-digit
calculator at an antique mall for $3. No charger, so of course it
didn't work.

Finally got around to disassembling it - the six AA nicads had leaked
grossly but fortunately did little damage to the board above it.
Powered it up from a bench supply and promptly discovered that one
segment of one digit wouldn't light... not much good in a calculator
since 8 and 9 looked the same :(

But - I looked in my "LED drawer" and there was a little PCB with
eight MAN-3A displays mounted on it. I remember buying that out of my
pocket money at Radio Shack (couldn't have been Poly Paks because it
works) when I was about 12. And that was thirty-five years ago...

It was the same overall size as the one-piece (bare LEDs with bonding
wires beneath a glued-on red lens) display PCB that was in there. And
a battery and resistor showed that it had the same common-cathode
matrix, and even the same number of connections! I unsoldered the old
display and double-checked that the one digit's segment was indeed bad
- put in the new display, powered back up and it worked 100% :)

I even had two three-packs of AA nicads bought at Marden's (an
odd-lots store in Maine) several years ago because they were on
sale... so I installed them in the base, screwed everything back
together, the calculator is now working perfectly!

So that's why I never throw anything away. Who'd have thought that an
LED display stick I bought over 30 years ago would find a home in an
early 70's calculator... in 2009. Of course now I have yet another
vintage four-function calculator I don't need, but it still feels good
to fix something that would otherwise have ended up in the trash.

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