The blower on my furnace runs constantly since the power came back on after an outage. My HVAC guy thinks it's the circuit board, but I don't see anything fried front or back of the circuit board. I've read that it could be the hi limit fuse or limit switch, which would me a lot cheaper. Any directions?

The black module on the circuit board is a set of contacts that allows or disallows voltage to the blower. It sounds as if the relay on the board may be stuck closed. It sounds like you are not unable to remove the board and carefully match a diagram or your own drawing to rewire it. Take the board to an electronics repair center (phone first to make sure they are willing) and allow them to replace the relay on the board. If it works you will be greatly satisfied with your prowess and if it doesn't you will be none the worse because most service techs are just guessing when they change electronic boards. Time won't allow them to cost effectively repair boards. I have several dozen that could be repaired. You have the knowledge of the exact malfunction of that particular board so it doesn't need troubleshooting which can only be done on site.