AL303 alarm in delta servo drive indicates the synchronized signal of CANopen is sent too slow. This means the synchronized signal of CANopen is sent too slow.

1. Check if the communication quality of the circuit is bad. 
2. Check if synchronized cycle 0x1006 is the same as the setting of controller. 
3. Check if the setting of P3-09 is reasonable. (It is better to use the default value.)