[morzh]

Oh...forgot: this is the second time I have encountered that same problem: the first was in Zenith 6G001Y.
The volume switch-pot would not turn off: the indicator flag would not let it.
The culprit is the small lip the cam that mounted on the shaft pushes against to raise the flag so the black part would show when off.
The lip obviously gets bent a bit too much upright (at 90 degrees position) so when the cam pushes against it, it does not slip under it but keeps pushing into it. I took the needle-nose pliers, bent it just a little towards the cam, so the surface at which it pushes, become a bit inclined and the lifting force is generated. Plus added a drop of lithium grease. Then it worked.
However when I installed the dial face back, it stopped working. Obviously the dial was pressing against the flag. I had to install thin washers between the dial and the chassis to create a little space behind it, lest I spent too much time investigating, bending and unbending things. So far the only ramification is, I had to not press the pointer all the way when putting it back onto the tuning cap's shaft.