I had a GNX2 back in the day that I put a lot of hours of play on! Right on!

So, these are digital pedals and the power supply is 18.5 volts, I believe. Be sure that you're using the proper power supply for what the pedal requires. Be sure that your supply is giving at least the minimum mA load for the board as well. Even if the volts are there, the mA need to be sufficient. If that's all good, the next thing in the diagnostics would be to duplicate what the board is doing by finding which switch/button does the same thing. There you can find a starting point. You could have a faulty button or dirt/grime that is making a connection. That'd be where I would start. If the power is good and the buttons are free from sticking, you're probably dealing with a board malfunction.