Because there's a hole in my radio!
I've re-assembled my workshop K2 sans opto-encoder. For me, this is a better option than keeping all the loose parts somewhere they will get lost and forgotten while I await replacement parts. Believe it. Besides, the radio is still quite useful.
Thanks to an e-mail from Gary, YS1GR, in El Salvador I had a great "Duh!" moment when he suggested I use software control to tune the rig. And, thanks to Clint, KA7OEI, who left a long comment on the feed version of my post over on AmateurRadio.com, outlining steps he's taken in the past to repair or replace encoders, which led me to take the longshot chance that I could salvage what was apparently a bad, but repairable part.
If you've never seen the K2 encoder lurking behind the front panel, here it is with the back cover off. Down below are its guts, the stator with the two LEDs near the bottom, arranged to shed light on the phototransitors opposite in a saw-tooth pattern as the stator is rotated.
When I first opened it up I was hoping there was some kind of debris or a bug blocking one of the LEDs, but no such luck. So, next I tried an electrical check.
Nearly all encoders of this type take 5 VDC input, so using the variable PS I hooked it up and poked around. I couldn't visually see any light coming from the LEDs, but of course, if the LEDs are infra-red then my non-superpower eyes wouldn't detect anything anyway.
One thing I did notice was that the IC was getting pretty hot, too hot to touch. That's not right, but whether it's a symptom of the problem or my test I couldn't say.
Anyway, I decided it's best to replace it, but was being "cheap ham" when I recoiled from Elecraft's $92 price. Instead, taking Clint's advice I searched for an equivalent part on Mouser to see if there was something close. Indeed there is. I ended up ordering Mouser part no. 785-600128CBL, which should do the job. The key protrusion is on the opposite side compared to the Elecraft encoder, but since it uses cable leads instead of pins it should just be a matter of installing it upside-down. The best part, it's only $33. I'm still ordering a replacement Front Panel U3 from Elecraft, however.
In the meantime, the radio is available to me via either Flrig or Fldigi, and actually tuning is not difficult, since I can highlight a digit and use the mouse wheel to tune. In about a month or so I should have the parts and will try again to restore the radio to good order. I'm hoping that some insect or even a very small bird doesn't decide in the meanwhile to make a nest inside the rig. :^D 73!