When Things Go Bang - Troubleshooting 101
Now what happens if your controller dies and you can't get a replacement under warranty? First, make sure it's not dead.
There are a few simple tests that can narrow down the likely causes of failure.
Fechter's 1st rule of troubleshooting: Always check the thing that's easiest to fix first.
Loose wire connections are a frequent cause of failure. Finding them is not always easy. Check all the wires and connectors before ripping things apart.
That said, here are a few other tests you can do:
Does the red LED light up on the controller? If yes, then the voltage regulator and supply power to the controller is good. If no, suspect a problem between the batteries and the controller. Check the fuse and fuse holder. Measure the voltage across the battery input wires to the controller.
Do the "rollback" test. Turn on the controller (check that light is on) and try to push the bike (or scooter, whatever) backwards quickly, no throttle.
Turn off the power and repeat the test. If you get a strong resistance to rolling backward with the power on, then the hall sensors and low side FETs are working properly. There should be minimal resistance with the power off. If resistance is still present, check for shorted FETs. If the rollback test passes, but the motor still won't go, then suspect the throttle.
If the rollback test fails, check for shorted FETs and check the hall sensors.
To check for shorted FETs, disconnect the phase wires from the controller to the motor. Use an ohmmeter on low range (or autoranging) and measure from each phase wire to each power wire (6 combinations) and look for a low resistance. Any measurement that looks like less than a few ohms indicates a shorted FET. Normally, all the resistances should be in the megohm range, and may vary with time.