Following the first repair of the Wavetek 3001, I knew that there was another issue with the 400Hz modulation oscillator, it was doing some "FM" oscillations so in practice I could only use the 1Khz tone.
Troubleshooting and comparing with the 1Khz oscillator, it was visible the waveform at C6/CR2 junction oscillating/FM'ing a little. Interesting enough by probing with the scope at the drain of Q2 it disappeared. I tried first to swap C6 to no effect, then swapped CR2 and it stopped but trying with the diode in and inverted polarization it would continue the same so it was either wrong assembled at the factory or it's for the moment just masking any other situation, probably Q2.
Before the previous testing I replace IC2 with IC1 (for the 1Khz) to no good effect so decided the issues was not the opamp.
I left like that, with the diode replaced (used a 1n4148 for the
moment, didn't even checked the exact spec in the manual)
After demodulation on an envelop detector it's now fine:
..envelope detector circuit and input signal (-25dBm) without the 56 ohm input load resistor connected on the circuit:
..I might start an AM receiver from here...
Since it's a bit of a pain to take and access the modulator/modulation board I opted to solder the diode from the pcb track side and leave it for the moment, also left the original diode in place with one leg open:
Since some times the unleveled light still comes on I suspect further recapping at the internal modules might be needed in the future.
Have a great day!