This one was easy, decided to check first the mode switch at the entrace point and then going from there, I was thinking it could be aging of the LSB crystal since on a previous test while troubleshooting the other issues on the radio fiddling with the LSB trimmer cap hadn't notice any audio change.
There was no need to look further, the problem was obvious, a broken connection providing the 8v for the LSB BFO oscilator (in fact to the crystal switching diode in the BFO oscillator) and that explains why changing the trimmer position had no effect on audio, it was not even oscillating:
Relevant schematic part:
Now on to set number 1, the external ACC and the dial bulb to fix....
Have a nice week!
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