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

[grsbanks]

(01-12-2017 10:26 AM)AndiGer Wrote:  Maybe someone who is more familiar with transistors than me can tell the right one according to voltages. 25V or 30V collector emitter voltage? Or doesn't matter? Or need a Darlington version?

That 25V or 30V VCE is the maximum the phototransistor will tolerate. With tensions of around 5V floating around in there you're well within tolerance.

Without knowing how the printer is built I would guess that the output from the phototransistor is pulsed (alternating reflective and non-reflective segments passing in front of the opto-coupler) and put into a cleaner square wave form by the LM339, which is essentially doing the job of a Darlington couple (so no need for that type of phototransistor specifically). The software counts the pulses and thus knows the horizontal position of the print head.

There's a good chance that the component linked to by Hans will work as a drop-in replacement as long as the transistor is the same polarity as the original's.

G. Stewart