This is unlikely to be caused by a damaged microprocessor.
"CHECK POW5" usually indicates a blown power supply board.
Try fitting a replacement board and let me know if that resolves the issue.
Yes, that is correct.
Have you tried fitting a replacement power supply board?
The power supply board inside the receiver unit needs to be replaced with a new power supply board.
Ok, then to try repairing the existing board will be very difficult, especially since you have already checked everything and it all seems good.
Swapping in a good board is a very simple and fast way to prove that there is a fault with the existing board.
If you want to try repairing your board, then you are going to have to look at virtually every component and every solder joint, and even the condition of the board itself.
Start by looking for any obvious burned or damaged components, and replace them.
Also touch every solder joint with a soldering iron to reflow the solder joint, in case there are some cold solder joints that are causing the problem.