HP-67 Reads cards but does not write

[teenix]

When a non-protected card is sent through the reader, the write protect switch operates before the head switch. For write protected card, the opposite happens. If the switches are not properly adjusted, then the head switch may operate first telling the CRC chip that the card is write protected and an error will be displayed.

If you have a multimeter and the circuit of the HP-67, then you can check the switch sequence by inserting a card into the slot with the calculator turned off. This takes a little force, so you can also remove the motor and drive shaft to enable the card to pass over the switches easier. When a switch closes, it is shorted to ground, or negative side of the battery.

When looking down at the calculator with the back cover and CPU board removed, with the connecting pins at the bottom, pin #1 is on the left. GND is pins 1 and 2. HDS is pin 14 and the WPS is pin 17.

The HP-97 service manual has procedures for adjusting the switches and is the same for the 67.

cheers

Tony