Quoted from Zitt:Yuck. I'd have replaced those LEDs too... The crap brown color is a good indication of poor IR transmission as the Epoxy has "yellowed" due to emitting IR radiation for 30ish years. It's cheap at $0.74/ea insurance policy.
They should be this nice Blue/purple hue
[quoted image]
https://www.digikey.com/product-detail/en/on-semiconductor/QED223A4R0/QED223A4R0CT-ND/3907905
The main reason I mention this is I was having a lot of issues with my Optos and it wasn't until I went in an replaced every one of them with new ... did my flaky opto issues go away.
Did you change the receiver as well? Wondering what part number you used with the emitter PN linked above.
I did found this "matched" set.
QED123 https://www.mouser.com/ProductDetail/?qs=KIIz7VjqD7I4A%252bR7oPm1DQ%3d%3d
QED124 https://www.mouser.com/ProductDetail/512-QSD124?R=QSD124virtualkey51210000virtualkey512-QSD124
I'd like to use the blue emitters as it seems the Q123(4)s would be fairly easy to mix up with each other. Unless of course the pictures shown aren't correct. Can anyone confirm?