Ken - Welcome to the Corvette Action Center!
Here are 2 threads involving the issue you mentioned. In the thread I posted, my mechanic replaced my head unit at the same time that he replaced an actuator that was broken. In the other thread, one of our members suggested that resoldering the connections on back of the control board (or mother board???) fixes the problem.
Fix
or
Replace
If you're mechanically inclined or have a friend that is, you may be able to fix it yourself. If not, head unit replacement may be necessary.
Good luck!

Jane Ann