Repairing HP 65

I have two HP 65s that I found in my dad's office and would love to get working. The more promising is from the earliest known production week and had minimal battery corrosion. I bought a new battery pack. With the battery pack installed it will run on AC, but without the AC adapter it doesn't work at all. Even with the AC power, the card feed doesn't seem to work, though the lights blink when I insert a card, suggesting that the card sensor is alive. Does anyone have any words of advice?


Functioning with AC adapter and not functioning without AC adapter would suggest the brass metal which connects the two outer pins in the calculator charger socket are not making contact. Try cleaning that by sliding some emery paper between the pin and the brass for both outer pins, and turn it over too so you clean both the pin and the brass strip.

Card reader issues will be the switch not working, or motor is bad, (or worse case the hybrid chip motor control circuit is bad) either way you will need to disassemble the calculator to check and fix that.



Just one addition: Using a 65 with an AC adapter is a bad idea. If the contact to the battery pack is bad, you might fry the card reader amplifier circuit. Even if you are not running the card reader!


You were right. I thought the contacts were clean enough, but they needed a bit more scraping. So now I need to address the non-functioning card reader.
I've read and and I must confess to being a bit intimidated. I haven't touched a scope for 30 yrs and even then I was a novice. Is there anyone on this forum in the Twin Cities, MN who would be willing to lend their expertise?


The card reader motor is always powered from the battery. Always. This means that even with a good charger and perfect contacts in the calculator, you still need to have a good, charged battery pack to run the card reader.

I hope this helps!



You should need a scope to do some basic determination of the card reader problem. I'd suggest firstly open the calculator, and carefully removing the card reader motor by unsoldering the motor at the motor end, and testing it with 3 volts, just to make sure the motor is spinning.

If motor is good, I'd then remove the roller, and test the contact switches by sliding a card through the slot.


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