Got your PM.

I never realised these encoders were so basic.
It can ultimately only be the LED/circuit (should have a continuous voltage over the diode), the photo diode/circuit, or the output transistor/circuit.

Somebody like British Encoder (encoder.co.uk) might be able to repair it. They actually supplied the original spindle encoders for Cyclones, and they were very helpful when I needed a replacement, but I'm not sure how they'll handle a non-common encoder. Probably worth a phone call/email.


Other option would be a competent electronics repairer, but I'm not sure how you'd find one locally. If I wasn't so busy myself, I'd offer to have a look. I know one person in Brighton I would trust to have a look at it, but I'm not sure if they'd be willing to look at it, as their usual area of expertise is consumer/musical electronic repairs, but they have the kind of skillset to repair something more old school electronics like this.

I'm aware there is at least one person on here who has looked at electronics for other users before, but I've forgotten their username!