You could be having issues with a bad electrical connection in the 120 volt power distribution panel.
I would suggest getting some electrical grease, disconnect the 120 volt power from the rig, open the electrical panel.
Disconnect each wire one at a time. Inspect closely for any melted insulation.
Do each wire, paying special attention to the white(neutral) wires in the back of the panel.
Apply a liberal amount of the electrical grease and re-terminate each wire.
Again do one wire at a time.
Remove each circuit breaker, inspect the connection between the circuit breaker and the buss work. Coat the buss where the breaker attaches with a light coating of electrical grease. You may need to use emery cloth on buss work to remove any burnt areas.