Testing the HP65 or HP67 card reader sense amplifier

[albertofenini]

(11-17-2021 01:02 PM)teenix Wrote:  You need to isolate the WA WB and WE pins from the sense and CPU boards. This will also allow you to keep the 6 volts and GND connected to the sense chip with the calculator turned on.

The signal generator will need its ground connected to the calculator ground rail.

For write mode, set WE = 5V otherwise the sense head outputs will be disabled.

You can apply a 4-5V square wave of approximately 1KHz frequency on WA or WB and see what appears on the head coil outputs from the sense chip. I don't think the motor needs to be running for this test.

cheers

Tony

Thanks Tony for your reply

How can I isolate those pins ? Simply covering those pins where the card reader PCB interconnects with the CPU board ?
Would it be better to take the chip out of the PCB ? (I have some amplifiers already desoldered from their PCB)
Which pins are the the head coil outputs between HAC, HA, CA (I guess that's channel A) and HBC, HB and CB (I guess that's channel B)

Can I use the same technique to test RA and RB ?

Thanks !!


P.S. I'd like to convert the old soldered pcb to the more convenient versions with those micro single hole sockets where the
head wires and the motor/keyboard assembly wires can be connected and disconnected without soldering, what's the name
of those micro parts ?

Thanks