I may be getting an early 90's ETC Expression for free. The problem with it is that sometimed when you turn it on the grandmaster is at 00 no matter the physical grandmasters location. Giving the board a rap between the faders clears the issue up. The board has been sent in for repairs twice since the school got it about 12 years ago. This is it's third strike and it has been replaced with the Express 24/48 from our main stage which is being replaced with an Ion. Any idea what's wrong with the Expression?