Daikin AO fault

[Andy's T]

Hi there can anyone help I have a daikin split with an AO fault code which I have found the meaning of the fault from the daikin fault code list but have no idea how to fix this fault as I have never come across this one before.
Thanks

[marc5180]

A0 Detect open or short circuit between external input terminals in indoor unit.

Actuation of external protection device.
Improper field setting
Indoor PCB fault

Have you checked the external protection devices?

Is there an External protection device connected between terminals T1 and T2 of the indoor unit terminal block.

If not on/off input from outside (mode No12 first code No 01) has been set to external protective device input ( second code No 03) by remote controller - if it has then change the second code numb to '01' or '02'.

If it hasn't then replace the indoor PCB