HP-67 Reads cards but does not write

[Trevor Gale]

(02-10-2024 01:31 PM)teenix Wrote:  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.

Hi Tony,
The WPS 'finger' was indeed not making contact with the gold pad on the reverse side of the keyboard board. I traced the contact pad to pin 14 of the processor card which leads to pin 3 of the microprocessor chip.

I turned the WPS finger screw 1/4 turn clockwise, watching carefully with a card inserted and non-inserted. On re-assembly with all the self-tapping (black) screws back where they came from and checked again with a multimeter between 'ground' (-ve) and pin 3 and pin 5 (HDS) of the microprocessor chip and the contact are made as they should be.

With a fully-charged battery (no charger connected to the calculator of course) I inserted a card with a known working program on it - it was brought through the reader no problem, but now it gives an error on reading. I tried this with both a write-protected card and with an un-protected card, both with the same program. I checked the cards afterwards in my HP-97 and they read perfectly.

There is a speed-control preset potentiometer on the CDC card, and I set this 1/8 turn to the left and then 1/4 turn to the right, then back to the original position - this made no difference to the result but did change the speed of the card pass-through, as expected. I also checked the eccentric spindle for the feed gear and the card is pulled smoothly through the reader - although now there is sometimes a short extra motor-on time after the card has been passed.

As I mentioned, there is no question of a 'gummy wheel' or any gummy waste left lying around anywhere in the reader.

I have repaired quite a number of HP-41 card readers successfully, and also one of my HP-65's successfully which out of curiosity I wrote and read a program card using a card from the same batch of cards I have been using, also perfectly fine!

Would you have any further ideas please?