HP 67: charging of battery pack

[BobVA]

(04-26-2017 05:59 PM)PANAMATIK Wrote:  3.) I removed the charger from the mains, while calculator is still swicthed On. The calculator gets dark, has no voltage, because the battery is disconnected.

Oh yes! That's what would happen, but it's just the logic PCB that is disconnected from the battery by the leaf switch in the charger jack, not the card reader electronics. Further down in the thread, Tony said:

Quote:...BUT in the 65 and 67, the sense amplifier chip is connected directly to the battery terminals. Not even the on/off switch is between them. If you connect an adapter to one of these machines, it relies on the battery pack acting as a shunt regulator to pull the voltage down. If the battery is missing or open-circuit, it won't do this, and the sense amplifer chip will get 15V across it. Even if the machine is switched off.

The original HP65 sense amplifier can be damaged by this. The later one, used in the 67, is supposed to stand it, but I don't want to risk it....

That makes some sense, as there must be an electrical path from the battery (and hence the battery charger when it's connected) to the card reader that bypasses the leaf switch, otherwise it couldn't provide current to "help" the card reader when the calculator is running on AC power.

This seems to pose a more perilous danger than that faced by the Woodstocks, since they have to be turned on without a battery for the damage to occur. (And they can be fixed by your ACT chip!) The ACT in the 67 would be protected by the leaf switch, but the failure would be a difficult to replace chip on the card reader.