Here is some information to help you solve the issues.
P1 error code indicates an abnormal voltage rise or drop.
Check the wiring from the indoor to the outdoor unit to make sure the wires aren't crossed or incorrectly connected. If the wires are properly connected then check the power supply to make sure the right amount of voltage is going to the unit
To test your indoor and outdoor circuit board,
you will simply have to verify the voltage frequency using a digital multi-meter. You will have to set your device on DC (direct current) and verify the voltage between terminals L2-S or for some models it would be between 2 and 3 on the outdoor terminal block. The result should be fluctuating between -50 and +50 VDC alternatively. If the the voltage fluctuates with only positive or only negative numbers, this indicates that the outdoor mother board will have to be replaced. If the result remains constant and there is no fluctuation at all, the indoor board will have to be replaced.