HP-67 Card Reader became very touchy

[Alevin]

Thank you all for your great advice an encouraging. I am learning quite a lot, being in mind I am an vulgar hobbyist without an electronic background.

Lets update.

To avoid uncertainty about the condition of the substituted C6 45 uF capacitor on the HP-97, as its capacity measure on the PCB was so different form the nominal one (on contrary to the others caps around), I took a breath ( be careful or you tryng are going to make things to worsen) an desoldered it.

Once isolated, C6 showed 44uF , just nominal capacity and 0,1 ESR. So it was OK. Nevertheless, I substituted it again for another new one. Curiously, with the logic PCB dissembled from the calculator, once a new C6 was soldered again, the measured capacity on the PCB went “overload” (above the measuring device maximum range). Never mind, as I am sure the cap and the soldering was ok an quick, without any overheating

In the same logic PCB dissembled, all the diodes were not conducting on inverse polarization, and they kept like this when reassembling the logic PCB on the rest of the calculator body, except the diode CR5, that shown again 1.4 K Ohms in inverse polarization.

As expected, this new C6 substitution did not solve the “only read card at low bat” problem, but at least I am sure that the C6 cap is now Ok.

So I am planning to substitute now the C4 6,8 uF cap (16 or 25 Volts on card reader PCB, as you and some other people have notified problems with it in the HP 65 67 97 card readeres. ( I can not find were is the other 2,2 uF mentioned by Hiwi).

In the way I will check and clean al the suggested components you all have mentioned.

Stay tuned.