Strange HP-45


My HP-45 is acting strange :

1- Entering number is not possible. Only one digit number can be entered.

2- calculation on one number is possible except for trig functions. The screen get blank and stay like this until off/on

3- If i multiply a one digit number i can get a 2 number answer and use it for other calculations except trig.

4- pi key gives 0.00 !

5- the timer is working ok.

What can be wrong?


FWIW, I only once had a calculator that basically worked but gave strange results. It was a Commodore SR4190R that could be fixed by replacing the capacitors. This is just an uneducated guess: The registers were flaky due to this capacitors being unable to hold charge. Others might know better.


Sounds like a plausible cause. Although the HP to my knowledge use tantalum in contrast to cheaper Japanese calculators that mostly use electrolyte capacitors.

But can also be cause by bad solder joints, a damaged transistor in the power supply, loose connection somewhere - most likely the power switch if we presume the calculator is not damaged by leaking batteries. Yes the battery compartment can look great clean (someone cleaned it at some point in history thinking then all is great) while in reality the calculator can be quite "rotten" - especially if you bought it used and therefore don't know if there has been a leaking pack in there. I've seen that a couple of times.

Really only one way to know for sure. The power switch can be rules out fairly quickly. "Massage" it see if behavior changes. If not it's most likely not the fault. However if is then great news because that's an easy place to fix. Otherwise the only way to know is open it up and look/measure to find the fault. Of course it can also be a bad ROM in that case you're out of luck and the only way to repair is buying a trashed one for donor. Here you can choose one damaged by leaking as the ROMs are far from the battery compartment. Either solder out the ROMs or just swap the main boards.


One of the battery leg is green and a small touch to the switch gives strange erratic display... Should i open it?


One of the battery leg is green and a small touch to the switch gives strange erratic display... Should i open it?

You decide. But it sounds like we've found the cause. Personally I would do it. Of course to clean the switch and relubricate with some appropriate contact grease but also the see if there's any leaking and green PCB tracks that needs to be fixed (although they might still work but if they're green they're corroding away).

On the other hand. Since you're asking I don't feel confident you have the skills and so risk doing more damage than repair. The best you can do is find a person (preferable family or buddy) who is confident repairing/cleaning such things and get him to help while learning you. Just my two cents. The ultimate decision is up to you.

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