HP 10 printer issue

[teenix]

Is it possible to notice a change in print head speed when this happens? ie a slower motor speed.

The motor speed is controlled by U2a and a 1V reference output from the Vref/Oscillator component package fed back into the PICK circuitry internal to the IC package. The linked post mentions a poor power supply causes the problem and this may upset the reference voltage causing printer motor speed variations.

Have you measured the power supply rails when printing fails, maybe there is a voltage drop. This may cause the PICK chip motor drive circuitry to change the motor drive pulse widths.

If you have a storage oscilloscope you should be able to capture the pixels being printed on any print row to see if they are changing pulse width and thereby stretching the printed pixels. If they stay the same width then the printer speed is the only other thing that can cause a stretched digit. Maybe try row 1, IC pin 25 output.

Why just with 0's, who knows, somewhat strange.

cheers

Tony