HP-19C Printer

[Jonas Sandstedt]

Hello Tony,

I have thought a little about his, and as I understand the problem, the calculator works normally until a print command is given – is that correct? If that is the case, my experience of these calculators is that if the printhead does not move when a print command is given, which is detected by the print head home switch, an Error message is provided. For one HP-19C with these symptoms this was due to a simple thing - one motor connector lead was broken. When the connection was fixed, the motor was running again and no Error message appeared.

What happens if you manually move the printhead away from the home position and then turn on the calculator?

The HP-97 repair manual states:

“2-29. When the PIK gives the command to move forward, transistors Q11, Q14,and Q9 turn on. Transistors Q12, Q13, and Q10 turn on to reverse the direction of head travel.”
Note: The three latter transistors are not used here since the DC motor only travels in one direction in the HP-19C.

“2-31. The printed line width and character-to-character spacing is determined by the speed of the dc motor. To control the speed of the motor, U4 samples the output voltage generated by the motor when the driver transistors are turned off and the motor is coasting.“

Have you checked if the PIK command is sent, and is so, where does the DC supply to the motor stop in that case? If there is an erroneous or non-existent PIK command, this could perhaps be due to faulty speed control in U4?

Hope some of this could be of help, perhaps you have already checked it all.

Best regards
Jonas