What letters / numbers that appears on the screen?
If the display is normal, and you can switch to other banks, and can edit each bank, then the problem of no sound, is at the pre-amp IC input, output amp, or CODEC converter.
This is the overall image of G1X inside.
Next, we zoom-in
the middle of picture above.
See the next picture.
IC2 (left) is input pre-amp IC (NJM2100).
IC4 (middle) is the CODEC IC (WM8734).
IC5 (right) is the IC output (NJU7082).
Test whether the input IC is working normally, turn ON G1X, plug the guitar, go to BYPASS/TUNER menu. When the TUNER function could work, certainly input IC is not damaged.
Means only two possibilities, namely CODEC and output IC. That is not easily tested, except in specific ways.
May also, there are problems in the input / output socket.
Turn ON G1X. Try the following (see figure below):
- Test the output socket. Touch pin output socket (right red arrow) with finger / screwdriver / whatever. If sound is heard in the amplifier, the output socket is normal.
- Test the input socket, Same as above. (left red arrow). (if this happen in this point, problem is clear).
If lcd light are on (as you say), but appearing G1 or d5 or bt, and the system are hang / frozen, this is a different issue to the one described above,and dealt with in different ways too.
References IC datasheet: