Could this be possible, mine has the same problem… it always dry signal, but the LED lights up… I think the problem could be in the Switching FET or in the mixing stage after the LM358. I don’t really know… I tested the signal path, seems to be right… tested the voltage for the ICs, all’s receiving it… I don’t know, it just stop workin.
Could someone send me the original Schematic? need to know exactly what’s hat 100k trim do… I think is to adjust the frequency for the CD4047… I’m not sure.

Regards,

Eddie