Any way into an HP-28S?


I've just picked up a cheap HP-28S. When I first turned it on I got a normal looking display.

I then turned the calculator off and opened the battery cover to check for corrosion. (It appears thee once was some...)

On replacing the battery cover and turning on the calculator I was greeted with a single black line across the display that slowly faded. Then nothing. The system reset doesn't work.

I think that maybe there's some corrosion inside, and I'd like to open it up to check it out (and clean it up).

Can these calculators be opened?


Any other thoughts on the problem. (the batteries are OK)


The problem turned out to be a slightly corroded batery contact. What fooled me was that it turned on the first time. Must have been enough leakage over the corroded contact to charge an internal capacitor????

Anyway, now I find that the second column on the left keypad sometimes doesn't work (more accuratly -- only rarely does it work).

It appears to be related to moving the hinge between the halves of the calculator.

Does the connector in here break after a while? (This calculator has definitely been used)

Can I get inside to fix it?


After some fiddling I managed to take off the hinge of the HP28, and then discovered that flexing the right half of the case just under the display makes the second column of keys on the LHS of the case work.

It appears there's a broken conection under there.

I suspect the HP28 is full of heat stakes, but is there any way of getting into the RHS without doing too much damage?

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