ETC ion wont power up

Hello

I have an ETC ion that won't power up at all when pressing the power button.

To make it short, i am an experienced technician, and I made a test to make sure that the power supply is working or not, and I found its working, shorting the green wire to GND makes it run, so all good, all voltages are OK.

Connected the connector back to the mother board, shorted the wires again, mixer powered ON, the PRESSED the power button on the MIXER, turned into BLUE. then mixer is working fine.

Any clue what's the issue?

I suspect the main board indeed, 

Please help

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