First of these looked as though a failure of the tuner block. Owner bought
another one for spares, removable front display missing.

This one has exactly the same fault symptom so more likely a problem with
the front panel (or improbable same tuner fault on 2 separately acquired
units).
Tuner will go into auto strongest signal search and store in memory and also
readout follows manual input of frequency and stores in memory but at no
point does the audio come through to the output amp.
Pressing the presets shows the frequencies but no audio. Injecting local
modulated RF in there and audio is outputed and stays invariant on pressing
any preset so stuck on one RF tuning setting. So not a false muting problem

Some of the main chip SM solderings seemed suspect so redid the non LCD
segment ones. Cleaned the 14 pin front to interior header plug. No stuck
closed keys. It looks as though the front has been kneed at some point as
the ring around the rotary encoder button is cracked but no pcb problems
found.
The LCD clock, CE and data lines between the 14 pin header and the 64 pin
chip trace through. Not possible to scope anything on the board without
making up a one-off extender cable.
I'm assuming some data problem but what changes between sending data to and
from the tuner to load the presets and normal listening mode?
Schematics are out there for this model