E301—communication error

main board have not received right date last 3s

Trouble shooting procedure
Connect the operation panel, test resistance of C45/C46 on the main board: Around 5.5K; Supply power by 80V isolation transformer, test voltage of C45, around 4.7V; Voltage of C46 around 4.9V.
Resistance between 2 legs of C15 and negative point of C4: around 3M; supply power of 80V, voltage of standby is 3.1 V. The resistance between 4 legs of U16 and negative point of C5 should be:2.1K; Supply power by 80V isolation transformer, test voltage of standby: 3.2V.
Connect the operation panel, supply power by 80V isolation transformer, check voltage between 3 legs of Q4 on operation panel and negative point of C7 is around 4.7V, Voltage between Q1 and negative point of C7 is :4.9V.