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

[Hans Brueggemann]

out of curiosity, i dug through the hpmuseum USB-stick and checked the HP82143 printer service manual.
according to the manual, this so-called encoder is indeed an IR-LED / NPN combo.
part number printed on the component is OPB2607, but seems to be unobtanium now.
i tried some quick & dirty testing with one of mine (fully functional), using a handheld DMM and found this:
1) checking the IR-diode:
put DMM to diodes test and connect DMM plus to red wire (it's actually 2 wires, red and white). connect DMM minus to black wire. DMM reads approx. 1 V.
2) checking the receiver NPN transistor:
put DMM to OHMS mode (seriously) and again connect DMM plus to red wire. connect DMM minus to green wire. DMM should read "overload" or "infinity" or something that indicates an open circuit. now, take your TV IR remote and hold its transmitter LED directly against the encoder's window. press and hold down a button on the remote. DMM should now give irregular readings in the kOHMS range.

note that DMM readings may vary with meter brand (i.e., OHMS sourcing current). so, ymmv, but you get the picture.