HP-97 Power/Charging Problem


I have a HP-97 that I purchased from a Cal-Tech student while attending Pasadena City College in 1979. I haven't used it in a while but I recently moved and came across it. I found that the batteries were NG, so I replaced the battery pack with SANYO Quick Charge NiCad batteries, N-1200SCF. They are 1.2v, 1100mah units. After reassembling the pack, and charging the pack overnight, I turned on the calculator and right away within a few seconds had a low-battery LED indication. I then removed the pack and measured the voltage...below 3 volts. When I assembled the pack, each battery showed a voltage of approx. 0.7 volts per cell. Obviously, the pack did not charge overnight. Today, I have placed the pack on an external charger, charging at 280ma (max is 350ma for quick charge). A previous check about an hour ago showed the pack at 5.63 volts. I'm sure that I have a problem with the charging circuit of the calculator. Does someone have a schematic of this circuit that I can use in troubleshooting this problem?? Any info would be greatly appreciated. TIA..sok.


There is an HP97 service manual on the HPMUSEUM CDROM set.

Things to check first are the battery contacts in the battery box and the charger contacts at the plug. Also the charger wires are prone to breakage in the plug at the calculator end. Check the voltage at the charger plug while flexing the cable around.


David, Thank you for your response. I had checked the charger and had voltage, but I had not checked the connector plug at the calculator end of the charger. When I did, there was no voltage. Problem Solved....Thank you, again....sok.

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