GE Microwave model JVM1331WW05 intermittent problem with control panel. To begin, everything works fine and oven heats correctly, timers, etc. However, the "clock" LCD will not stay lighted up. It can be reset by unplugging the unit and will light up, then will quit and clock buttons will not function. Eventually, all buttons will not function and must unplug and plug back in to get the microwave to work properly. I suspect the control board (circuit board) but would appreciate some direction before spending money on parts. Thanks for any help.