Cardreader problem...


I have a perplexing problem with a HP-67 cardreader: It reads and writes cards perfectly when running on battery alone but always errors on battery+charger. Ive changed chargers (the outputs are the same anyway). The motor voltage is within .1V between battery and battery and charger - this one has me beat at present so all ideas gratefully received.


Are your nicads in good condition?

The problem could be caused by excessive ripple. The nicads are probably used in the 67 to both regulate and filter the rectified AC from the charger. (I say probably, because I'm not familiar with the 67, but that's how many other models do it)


It sounds like his NiCads are fine since the card readers works on them without the charger. Have you tried another charger on it? I suspect something is wrong in it. Perhaps a bad filter cap or bad diode is letting AC ripple into the calculator.


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