Boss Poly Octave OC-20G Owner's Manual page 15

No effects are being applied.
Is the GK-2A's selection switch set to "MIX?"
When set to "GUITAR" or "SYNTH," the necessary signals may not be
input to the unit, which may prevent effects from being applied.
No effects are applied to sounds input to GUITAR RETURN and normal
pickup sounds.
Noise is produced.
Is the external device connected to the GUITAR RETURN jack working
properly?
When the GUITAR RETURN jack is used, the signals input to this jack are
used instead of the normal pickup sound.
Therefore, noise may be produced when you've failed to switch on the
external device's power, or you haven't hooked it up properly.
Is the GK cable securely connected?
When connecting the GK cable, insert the connector completely, until it is
locked.
Troubleshooting
15