So the PCA board, Uno and connections/communications between them are OK
Go back to your external supply. Don't forget to disconnect v+ from the Uno, and measure the voltage between the 5V and GND pins on the servo connectors. What do you see ?
So the PCA board, Uno and connections/communications between them are OK
Go back to your external supply. Don't forget to disconnect v+ from the Uno, and measure the voltage between the 5V and GND pins on the servo connectors. What do you see ?