HP-65 motor always on - card reader

[Trevor Gale]

Hi Tony,

Yes, I also looked up the various chip info, and the connections, and functions, are the same.

Interestingly, from the HP-41 service manual from HP, the card reader circuit uses 1826-0322 for the 'sense' chip; however this same chip is also used in the HP-67. In both the '67 and the '65, pin 1 of this chip is the +ve supply to the motor, supplying the +/- 180mA for it - whereas in the HP-41 cardreader that pin drives a LED which couples to a phototransistor which (in parallel with the HDS switch-to-ground line) then activates a timer which actually drives the motor through an emitter-follower.

I do not see any problem with using this chip - and I will today attempt the replacement and get back to you.