HP-19C Repair Odysee

[PANAMATIK]

A next milestone for the newPIK chip is achieved!

Today for the first time I placed the newPIK prototype board on the HP-19C printer board. With keyboard buttons, which are only test buttons for now, I was able to drive the motor with PWM controlled different speeds. The FWD, REV and BREAK signals are working as expected. With the PRX button I could start the line printing sequence, the motor moves 1s with slow speed forward, then with full speed backward until it reaches the HOME switch position, where the motor windings are shorted 1/2 s for fast stop. This works very well.



HP-19C main board with newPIK prototype stacked on "printer/power supply board"

One problem is left: The VM signal (Velocity Motor?) goes Low during the PWM Low phase if the speed is too slow, but the High level is only 1.8V, I cannot read it on TTL digital input. Therefore I cannot regulate the motor yet.

There next tests will be: regulating the motor speed by amplifying the VM signal
and, last not least, driving the printhead pixels.

I hope this will be done soon, then I can draw the schematic for the newPIK. I have also the idea to include infrared printing for the unfortunate cases, where the printhead is damaged, then the newPIK will be able to make these HP-19Cs printing again by sending the identical lines to the HP82240B printer, when an Infrared diode is installed.

[Edit: One day later I can regulate the motor speed and adjust the speed with the 50k Poti. I achieved to read the VM signal on an analog input every ms and now use it for regulation of the motor speed, also the 7 pixels printhead pattern is output every ms]

Bernhard