I'm trying to get a feed from an Alexa Classic to a Marell transmitter via an AJA HD10MD3. The feed is working fine from both Mon and Rec outputs. The onboard monitor is fine, but regardless of taking feeds from the camera or the loop outs on the monitors, I can't get the AJA HD10MD3 to lock to any of the feeds. The lock LED just flashes on for a second or two, then off, then back on again etc. It sends a little bit of an image while the LED is on, but it's very under and black and white.
If I run it via an Atmos S2H and then convert HDMI to Composite, it works fine.
Has anyone got any ideas, or encountered a similar issue?