Chosen Solution
The power board I suspect is ok. I’m thinking the I/O main board is needing reset
Mike Speed follow the flowchart and measure the voltages. Let us know what you find. If unsure post some good images of your Boards with your QUESTION. that way we can see what you see.
If there is a fault coming from screen or T-con to main board, the main board will lock itself after 3 failure. To lock out main board you need to reset it by for example service remote from china. The result of locking main board will be: you turn on, hear clicking relay - black screen - after 3 sec clicking relay again off.
