[oneolddude]

It is a GE profile side by side refrigerator and has stopped freezing/cooling.
The control panel in the frig isn't working and I suspect the mother board is bad. How do I troubleshoot the mother board? Does it have a diagnostic mode, or does it have test points that I could get voltage reading? Can I by pass the mother board to make sure that the other components are working, like the compressor?

[richappy]

You can refer to the schematic behind the control panel/encoder to check voltage to it, but generally all manufacturers do not give board details and when one fails, even a new one, the suppliers don't want them back, just throw it away.
This board controls almost everything in the fridg so the board is probably bad. Just make sure that all the loads, ex. evaporator fan motor, etc where working before failure, otherwise a bad load will blow out the new board.