Hi Pablo,
I had this problem a short while back.
Try resetting the affected controller using the following steps
- In the RC Settings, put the remote status to "OFF" then put it back to "Slave".
- Press the C1 + C2 + trigger (photo) buttons and keep them pressed and TURN OFF the controller.
- By still keeping pressed the C1 + C2 + trigger (photo) buttons TURN ON the controller.
You will need to pair the controller with the master again but then you should have your video downlink back
If no luck, try resetting the master and then the slave.
Hope that helps.