Warren....Worth a try! Are you comfortable carefully removing or moving the sound board and power board and then re seating them? If you pull them all he way off make sure the pins line up going back on. Idea here is that corrosion may be the problem. Sometimes moving and re seating will get them working. Without working spare boards to try that's about it for me.
GRJ GGG and others are a lot sharper on this then me.
Richard