HP 67 Card reader Troubleshooting

[Gene DiResta]

I have an HP67 that reads cards well but generates an ERROR message in the display when I try to record a program. Please email me any information that would help repair/troubleshoot this problem. Thank you

[David Smith]

Your problem lies in the write protect leaf switch in the card reader. When you disasseble the reader you will see the gold colored comb of witch contacts. When you insert a card, little nylon balls are pressed against the leaf switch contacts causing them to touch pads on the back of they keyboard circuit board. On each leaf switch contact is a tiny screw that adjusts the contacts. It sounds like the write protect switch is permanently closed. I don't rememebr which one it is, but you can trace the pads on the keyboard to the contacts along the bottom edge of the circuit board. There are three contacts (motor, head enable, and write protect) that should close and open in sequence as a card is inserted and read. The switch adjustments can be very finicky and they can also interact with each other.

[Tony Duell]

I agree the problem is most likely to be with the leaf contact -- although it could also be the Card Reader Chip on the logic board (the largest chip on the board). However, if the write protect contact is permanently closed, then the calculator will think all cards are write-enabled, and will not give an error on writing.
I believe HP modified some calculators (maybe only 97s) for in-house use by connecting a toggle switch in parallel with the write protect swtich. When it was closed, the machine would write on 'clipped' cards. This was sometimes used to re-write Program Pac cards, for example. How it seems to work is that the calculator looks at the state of the write protect switch when the card-at-head swtich closes. If the write protect switch is closed at that time, then the machine assumes the card is not clipped, and will write to it.
Anyway, for the 67 we're troubleshooting here, I'd start by cleaning (_carefully_) the leaf contacts and the pads on the keyboard PCB that it touches. If that doesn't help, try _slgihtly_ screwing in the adjusting screw for the write-protect contact, which IIRC, is the one nearest the display end of the machine.

[David Smith]

No, the HP logic wants seems to want to see a change of state on this pin. If it is stuck closed or open, you can see the ERROR message (just fixed one of these last week... don't remember what state it was stuck in though). I think the write protect bypass was achieved by a switch that connected write protect to motor start.