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

[AndiGer]

The foto coupler is one component welded together.
Didn't try to open up until now. See picture attached.

If I compare the not working one with the working one with a DMM I can not find many differences. Maybe I did not use the right measurement methods.
My findings:
Working one and not working one both give me only one result when I use the diode tester:
- on black, + on red/white 1524 and 1644 resp.
Using resistance tester:
- on green, + on red/white: if I cover the diodes gives open circuit, if I give direct light from a LED torch gives about 5.4 kOhms one the working, 3.2 kOhms on the not working one.

Andi