Bob Urz:
No.... it is not optical..... it has springy contacts inside that rub
against a rotating disc that generates pulses as you turn the control.......
the thick goo that seems to get thicker with age may impede the proper
contact. Clean out some of the goo (not all of it) and spring out the
contacts to create a firmer tension against the disc.... or order a new
control .... and plan to replace it in a few years.
--
Best Regards,
Daniel Sofie
Electronics Supply & Repair
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"BOB URZ" wrote in message

This is a optical type control with a led or such with a photo
interrupter,
correct? What's the goo inside doing, blocking one of the Photo
interrupters?

Bob