HP-19C Printer

[teenix]

I replaced the drive transistor with a BC327 and the motor worked and the carriage moved back and forward if I isolated the FWD line and applied Vss through a 1K resistor. This proves the drive circuitry works and the motor works.

However, if the motor is not homed at switch on, the motor does not home. If I manually home it, switch on and try to print I get a blank screen and nothing else which is what I saw should happen in the microcode. The home signal is appearing at the PICK chip and the hybrid package outputs the 1 volt feeding op amp U3a that senses the motor speed.

This sort of leans towards no motor drive signal coming from the PICK chip. I cannot see anything appearing on the scope either.

cheers

Tony