HP-19C Repair Odysee

[teenix]

(05-09-2021 02:34 PM)PANAMATIK Wrote:  

(05-09-2021 02:16 PM)teenix Wrote:  Looking at Tony Duel's circuit, the 50K pot should adjust the motor speed, and the 200K pot should adjust the intensity.

Exactly! But only if the circuit works properly :-(

Bernhard

Too true :-)

I'm pretty sure the HP-97 has full motor speed for reversing the carriage.

The PIC chip can gate the PWM signal from its VM pin so that the motor is controlled by the PWM or steady voltage for full speed.

The FWD output must also have circuitry to detect when the OPS switch is activated to stop the printer when paper has run out even though this is also done in 97 hardware. This is tested when PWM is present and when not, although I don't know if the 19C has this.

cheers

Tony