Testing the HP65 or HP67 card reader sense amplifier

[albertofenini]

I Tony,

I may as well unsolder those pins you are right

When testing write capability, where should I measure the output of the
signals that I have injected at WA and WB on the sense amplifier ?

Thanks and sorry to ask so many questions ...

(11-17-2021 01:54 PM)teenix Wrote:  You can't really isolate them without unsoldering them from the sense board. Definitely no good bending them or they will break.

The HP-65 schematic has pin details for the sense chip.

http://www.hpcc.org/cdroms/schematics5.0...c/hp65.pdf

The RA RB outputs require AC input signals in the millivolt range from the magnetic head. If you had a signal generator that gives AC sine wave output in that low range you could probably feed it into the (HA CA) or (HB CB) pins with the head disconnected. Or much easier, you could just activate the motor and feed a card though.

A GND signal on the MS pin will activate the motor. 5 volts will stop it. The MI pin will have to be at battery voltage also. The chip could be powered up from 6 volt, and separate 3.75 volt supplies with appropriate signals on all the input pins. Overall, it would be easier and safer to just unsolder the WA WB and WE pins.

I have not seen any solderless single wire to board sockets like that these days. They may be around but may have been ordered by HP at the time of manufacture.

40-50 years later, corrosion and oxidization will become a problem for some of these nowadays

cheers

Tony