I have a Jenn Air SVE47500b downdraft that we installed in our new home in 1997. It has been troublesome since the very beginning, but has now gotten to the point that it is basically unusable. Here's the history... Many, many years ago, the display gradually got dimmer so that now unless the room is totally pitch dark, it is unreadable. Honestly, this is not too big a deal, so I didn't worry about it too much, and didn't feel like spending the $300 for the new board to fix it. Recently, I began to notice that the oven was not venting properly - there was considerable condensation, etc., and it would eventually shut off and start beeping and I would have to reset the breaker, which seemed to bring it back to life. Now, however, the oven will not work at all - the burners are fine - and it will start beeping every few minutes. I have to shut off the breaker when we are not using it or else I have to push a button on the control panel constantly to stop the beeping. Even when I turn the breaker back on and the burners work, the oven will not heat. I do not see any fault code on the display. It just shows the time.
I am thinking relay board, but I didn't want to just throw a $200 part at it without getting some input from people who have some experience with these units, which I do not.
In short, here's the problems - random beeping with no codes, oven not heating at all, and oven not venting properly when it was working. I guess you could add the faulty display to that, but I don't know that that's related..

Thanks alot Simon! I will try your suggestions this weekend. One question - where exactly is the relay board on this unit? The schematics don't really show where it is...