Does your encoder knob(s) or Model Select knob not allow you to "PRESS FOR TYPE" ?
Don't fear, it may be a simple fix you can do yourself:
This problem is often the result of the cap being pressed down too far on the encoder shaft which in turn does not leave enough travel for the switch contacts to "make" a connection when pressed.
All of these control knobs are tapered on the inside with a directional shape for a "D" type shaft. The simple friction of the taper is designed to hold the knob in place. There can be significant variations between the molds for each of these plastic caps (I've yet to determine which mold has a tighter tolerance). In addition, the physical dimensions of the pot/encoder shaft can vary +/- .2%, add temperature variations, leaking mechanical lubricant from the pot itself, sweat, spilled beer etc. you get the picture. Typical use can easily cause these to slip towards the top of the case decreasing the amount of available travel for the switch function properly.
You may even feel a "click" with no result. At this point, there is another mm of travel or so before the contacts will actually close.
Removing the cap and testing the switch will prove if this is the case.
Two simple fixes:
1 - Remove all of the caps and reinstall each one starting with the encoder only. Find one with a firm fit that stops allowing enough room for the switch to work set it aside and continue until you've gone through them all. Choose for the encoder one with the most travel and press-friction (to keep it secure) and return the rest to the remaining controls.
2- If the above doesn't work, you can fix it by Inserting just enough tape into the top of the cap to increase the travel. The adhesive from the tape will keep the cap in place. This is important because the friction lock of the cap is reduced beyond the caps critical taper that would otherwise hold it secure. I suggest a small piece of double sided foam or gaff tape folded over, sticky side out, just enough to allow the switch to operate. Whatever you do DON'T USE GLUE! Logically, it makes sense to keep it in place. However, trust me, it will only complicate your life in the future. Using glue may render the switch useless if just enough were to leak into the switch cylinder.
If you find that the cap is not the issue, then I hate to be the one to tell you... you now have an expensive brick.
Just kidding. The encoder can be replaced with a part that's better than new. I use a replacement encoder that is slightly taller than the stock piece to keep the slipping cap issue from ever happening again.