HP-67: The Red Dot Low Battery LED almost always lighting


After rebuilt the lateral PCB (totally new, between the card reader and the CPU main board), my HP-67 works fine. But a small malfunction happens. Even the battery pack (3 x Ni-Cd 1.2 V) is fully charged, after few minutes, the Red Dot Low Battery LED (RDLBL, right – bottom on the display) lighting. The only way to turn-off the RDLBL is moving the ON/OFF switch 1 mm left => normal function / right timing. I cleaned the ON / OFF switch in order to avoid undesirable electrical contacts, but no success. I don’t know if a resistor / capacitor could be sick. Suggestions? Thanks.


It definitely sounds like a poor switch contact (high resistance) problem. First,clean both the switch contact as well as the gold contact points (traces) on the circuit board. Coat the contact and circuit board with silicone grease (dielectric compound). Finally, sometimes it helps to bend the contact out slightly to get more contact force on the circuit board.

Buena suerte,



I had the same problem when I used cheap rechargeable batteries. The problem disappeared when I replaced them.

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