HP65 card reader sense amplifier

[isanchez]

Dear all,

I am facing an issue with an HP65 card reader.

The card reader worked fine after replacing the CR board for the new and brilliant design offered in Etsy. I mounted the old sense amplifier chip, the pins, and the potentiometer... all worked very well (calculator and the card reader). I tested it intensively.

Then the calculator was connected to the wall charger without batteries (or maybe with them) and had a weird behaviour for some time (no keyboard reaction, random display), after this, using other wall charger and the battery pack, it worked fine, except the card reader: no reaction at all, like dead. I can hear clearly the "click" of the switch and nothing. The contacts are fine, the motor, the golden switches....all, because I have checked them and it worked flawlessly before this event with the wall charger.

I was wondering if the sense amplifier has been damaged or, maybe, the (small) capacitors (?) embebed in the board...

If the sense amplifier of the HP65 is damaged, may I use the one from an HP67??? In the schemas, they seem to be the same component, but they have different reference.

If you belive I should check another thing, please, let me know.

Thanks in advance and kind regards

Ignacio