Random shutdown, without any cable connected, PQLS flashing

Hello all I am trying to find the problem with the amplifier which i really would like to keep as we are in a financial crisis and repairs is more important then just thrown and buy new.

First thing tried was factory reset without luck.

I have uploaded the service manual hoping someone with experience can help me find the problem. I have a multi meter which I bought and have some basics electronics knowledge.

Thank you in advance.