Do you have a core module set like a Visual Cortex or Cadet I / Cadet II along with your set of Castles? You need a sync generator module and an encoder module to display valid video on a TV.
If rather you’re trying to input external video into the Castles, it’s not just a case of plugging the output of that AV2RGB converter directly into the modules–you’d also need to synchronize/genlock the camera to your sync generator otherwise your camera input will scroll. There are also a few input conditioning steps (clipping, DC restore, etc.) that an input module would take care of. None of these are readily available for purchase at the moment, unfortunately.
This post might help: