HP-97 Printer Malfunction

[Jonas Sandstedt]

Again thanks for all tips. I have checked the home switch, it reads 0.6-0.7 ohms in the home position and more or less infinite at the other end. I can’t measure capacitor values, but C2 is neither shorted, nor open-circuited. The motor runs very smoothly when powered manually by a finger, independently of if the calculator is powered or not, so I do not think there is anything that hinders its motion. When a printer action is required, and the whining tone is heard, the motor is powered with about 0.1 V DC. When the motor is manually moved such that the printhead is moved forward, the voltage is changed to about 5V for the properly functioning return motion. But I also noticed that when the motor is manually moved such that the printhead is moved backward (a very slight distance), the motor is powered in the forward direction, bringing the printhead back to the home position. As I interpret this, the motor may be electrically run in both direction, but in the home position it will not move. I cannot feel any vibration in the motor, but by listening carefully, it may be the motor that makes the sound.