HP-67 Card Reader became very touchy

[Alevin]

Being tantalum caps known to be robust and eternal, but sensible to over voltage, I wonder why these are so prone to produce fails in models with card readers. One possible explanation could be the situations where the calculator is working on the adaptor but without batteries inside. Even thought that Classic series are said to be able to work only on the adaptor, the open voltage measured on the adaptor pins are 15 volts , 5 volt. May be the models Hp-65 HP-67 with card reader suffers more the consequences of voltage surges when switch on and during work without batteries, as they detteriorate the power line cap (specially if it is 6 volts cap), and this may not have much impact in the other circutry and chips, but it does in the quites sensible reading logic.

Makes it sense?