Unplug the CN3 connector from the control board and check for 120 VAC between the Black & the Yellow wires at this plug. If the reading is correct, replace the smart board.
If the reading is incorrect, then you did something wrong in the previous tests.
- The smart board Part number: WB27X10894
Here are the breakdown diagrams and Parts for GE JVM1653SH06 Microwave - AppliancePartsPros.com