Calculator repair fun
ard at p850ug1.demon.co.uk
Mon Jun 8 13:04:50 CDT 2009
> This is a perfect example of why I never throw anything away...
I think that applies to most people on this list, or at least most
hardware types here. I certainly have things that other (sane?) people
would have thrown away years ago. And one day they come in very useful...
> 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.
> =46inally 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
Ah, yopu actaully sort your bits. I just have a houseful, and hope I can
rememebr where I've put things....
> 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 rememebr once repairing a friend's Novus calculator using a display
taken from a dead Commoodore machine. Like you, it looked the same, had
the same number of pins. and a bit of testing with PSU and resistor
showed the connections were the same (as far as I could test, the working
segments in the defective display were wired between the same pins on the
> 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.
One of my favourite HPs is a 'worthless' HP45. It's worthless because
it's in very poor condition (legends rubbed off, the display digits
aren't all the same size, etc). And the reason I like it is becasue I
built it from junk. A collection of bits from anotehr HPCC memeber. The
displays (3 off 5 digit modules) came off a couple of boards (which is
why they're not all the same size), the logic board has a A&R (Arithmetic
and Registers) chip taken from another board, and a transistor from my
junk box, etc. Works fine...
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