Powering a HP 67 without battery pack?

[teenix]

(05-28-2019 11:56 AM)Lode Wrote:  I heard a brief motor sound when connecting a DC voltage supply with 3.7V to the + and - terminals (with the calculator switch *off*). It also draws as much current as given (I stopped at 0.5 amp). But the calculator does not power on.

With the HP power supply connected to the 3-wire input, the calculator does work (so phew, that's not broken!).

So is it possible that the broken card reader is affecting how the power to the calculator itself from the battery terminals works, but somehow using the external 3-wire input with the official power supply manages to get around that problem?

How does one disconnect the card reader board? Are the screws under the sticker on the back? Shame to have to remove it in that case...

Assuming the power leads were connected correctly, it sounds like the sense chip is faulty and probably has some sort of short. If so, the chip may get warm (hot) with power applied. The motor should not turn on unless instructed by the CRC chip. You could disconnect the battery (red) wire from the motor and see if has seized by applying 3.7 volts to it. I think the capacitor on the motor connectors is polarity sensitive too.

It might pay to check the internal wiring from the 3 pin plug to the card reader board. I'm guessing the battery charger won't deliver the same current as your external supply.

If desired, you can unplug the card reader board from the main cpu board and unsolder the 4 wires and remove the board entirely. The calculator still works but whether this will ultimately cause problems, I don't know. The RA RB inputs to the CRC chip will be floating, but that may not matter.

cheers

Tony