Thank you all for your suggestions. To respond to each:
- Mirek - yes, electrolytics are fine
- Glen - the decoder does decode on the LCD when transmitting. Earphone jack looks ok, and it did work at first. I did hear a power on click today, so something is getting as far as the earphones.
- Alan - actual voltages IC10 pins 1/2/3 10.8v, pin 4 0v, pin 5 9.6v, pin 6 9.7v, pin 7 11.0v, pin 8 11.6v; More interesting perhaps, Q7 D 0.4v, G 0v, S 0v. S is grounded anyway.
So could the problem be a permanently muted rx? Looking at the circuit, there doesn't appear to be much around Q7 which could be a more likely suspect. Could Q7 fail gradually? I had assumed, maybe wrongly, that it either works or it doesn't.
Conveniently, I do have some spare BS170s from another project. Sod's Law applies of course in that the solder pads for Q7 are under the gain pot, making resoldering or removal a bit of a game! They are not shorting to the pot above nor do they appear to have any short between them. I did look quite carefully before soldering the pot over the top, for exactly that reason.
Any further checks I can do before pulling the board apart? Of course, that may not be the only issue, but at least it's a start. Thank you for that.
73 Chris G4CWS