HP 82143A / HP 82162A foto coupler (encoder) - substitute

[AndiGer]

First off all: Thanx a lot for explaining and your efforts - especially the diagrams by Jose.

This evening I did some measurements on the defective printer.
Red <--> ground: Battery voltage, about 4.87 VDC.
Green <--> ground: If I rotate the pulley manually voltage will change with each movement, but no regular pattern. Voltage varies between 0.4 to 4,65 VDC. If I cover the coupler's "window" voltage drops to 0 VDC.
When I turn the pulley slowly from home position to left hand wall I have about 20 high voltage of 4.82 VDC at pin 13 of U3. In case of high voltage at pin 13 the voltage at the green wire is between min. 3.65 VDC and up to 4.65 VDC (sometimes goes up to the higher value when slightly turning of the pulley). This is the 3k2 one.
Black <--> ground is 3.65 VDC constantly.
Measurement of the 2 resistors give required values: R10 = 120.2, R11 = 26.7 k.
Pin 3 of U3 has 14.6 VDC.

I will check the count of high voltages at pin 13 of U3 in the working printer and report. Maybe this will help.

Andi