HP-65 card reader - purpose of WE pin

[teenix]

(05-02-2019 11:12 PM)albertofenini Wrote:  Hi Tony
This is an HP65 so you don’t get any error message
With the switch in W/PRGM the card goes thru
The waves WA and WB look clean and ok and the display is steady like everything was ok
But if you try to read the card just written you get a blinking display
I’ll check the switches and report here

We have another unit that has a noisy WB and doesn’t write as described in a
different thread but this is the first time that with good waves the card is not written

We have of course tried a bunch if new cards and not just one

Any suggestion is welcome ! Thx in advance

The switches in the HP65 look like they do the same functions as the HP67/97. The reader chip has a different serial number, but look essentially the same and I would imagine function the same although they may have been improved with later models. The HP65's main difference is in how the data is transferred to and from the calculator's memory. That process is directly controlled by the CRC where as the 67 is by software control.

If the wave forms are looking ok, then assuming the PSU, CPU, motor speed, caps, connections and cards are ok and the RW head is clean, then that just leaves the sense chip and RW head itself as the probable weak link. They could be faulty due to age and may only ever work "some" of the time or not at all.

The data going into the sense chip on the WA WB lines won't necessarily reflect the data coming out of the RW head onto the card surface.

The head, through years of use, could have a flattening of the usually rounded surface which the card rubs over during record/playback. The gap could probably be taken up by the cam adjustment, but if the head is really worn, this adjustment might not suffice. See attached. This calculator has read errors and I can clearly see data bits missing on the RA RB pins. The card reads ok on a different 67.

The writing probably has enough energy from the worn heads to change the magnetic state of the card surface though a mildly worn gap, but would be less effective.

Reading that data back I guess would be problematic in these circumstances as a worn or a good head tries to read the weakly recorded data back.

The actual head itself might be "weak" especially if it has become magnetized.

I don't think the 65 detects card errors other than write protect and the RUN/PRGM switch in the wrong position as there is no checksum saved to the card.



Edit: My bad - I don't even think the RUN/PRGM switch is tested either, wouldn't make sense :-)

cheers

Tony