The AC separating point 7707 fault can be extremely tough to troubleshoot. Please be sure to review the schematics for your specific inverter, not all models are the same.
You should always have a diagram available when troubleshooting and verify signals before testing.
Here are some of the most common causes for a 7707 AC separating point fault:
1. Undervoltage Release Coil in the main AC breaker.
A) By removing the cover of the main AC breaker, you can expose the motor and coils. Use the schematics to locate all of the signals and test the operation. The 24Vdc supply comes from the ACC X9503 pin 1 and returns on pin 2. Be sure to test at the source to the coil from the top of the Main AC breaker. The photos below show the location of the ACC board and the related supply/return signal for the UV coil.
B)
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C) 
D) - E)
2. Activation coil or motor failure in the main AC breaker
A) Similar to the UV coil, remove the cover of the main AC breaker to expose the activation coil. Locate and test signals. The 230Vac supply comes from the X9501 pin 1 on the ACC and the neutral is located on pin 5. Be sure to test at the source and the coil. Photos below aid in showing example test points.
B)
C) 
3. Other related AC breaker signalsA) Be sure to check all feedback loops.
B)
4. ACC Board
A) Occassionally, the ACC board can fail causing the 7707 fault to manifest. During the troubleshooting, you may have already found evidence suggesting the board has malfunctioned.
B)