Not a FLIR, but similar - Iris Thermal Camera not working

I have an older model Iris516 thermal camera on my boat that does not work. I get power, and the controller moves the unit as expected, but I get no picture on my Garmin MultiFunction display. I tried connecting a BNC to HDMI connector to try to get a video on my laptop computer, but no luck. Any suggestions for how to assess or fix this?