HP-19C Repair Odysee

[PANAMATIK]

Hi all,

As described in post #32 my HP-19C printer motor was way too fast, whatever poti position selected.

I checked the printer board transistors and components a thousand times, replaced ICs and compared the components and wires with a known good board: nothing to find. Then finally confused, I thought that the big motor capacitor did not have a value in Tony Duells schematics, I unsoldered it to measure its capacitance (1.5uF). Then helplessly I soldered it back to the motor, assembled the two boards and tried again.

And it works!



The capacitor wasn't soldered properly and had lost its contact to the motor, but it is essential for generating the VM signal, which controls the motor speed.



I printed on the same paper from the days before with the reverse printed number Pi. But now I could change the motor speed with the poti. "0.00" is printed with too slow speed, "3.14" with the right speed.

But this was not the "totally corroded" HP-19C, it was my second HP-19C. The challenge for the PIK replacement continues, and signs are good, because I know much more about the HP-19C printer now.

Bernhard