Production Switchers

We are currently in a three camera system, all Sony NX5U (yes, they're relics), feeding a Carbonite Ultra via SDI. The output from the Sony's is supposedly 1080i/60 (59.94). However, regardless of the output combination I try I can't keep the camera inputs from rolling even with the internal reference set to 1080i 59.94. What am I missing? 

I am aware of the IO Processors and the cameras do work when set to SD-FS (which I'm still unclear on the meaning). But I would prefer to do this without processors if possible. I'm considering getting an external reference but am unsure that would solve this issue.

I have also tried the same scenario utilizing 720p output from the cameras however I'm not clear on the output frame rate there and the manual isn't too helpful either. Any suggestions or help appreciated.

The SDI-FS means that you have enabled the Frame Sync for that input.

 If you do not have Genlock run to the Cameras that is the same as what is feeding the Carbonite then you have to use Frame Syncs to lock the video entering the switcher to the "internal" Genlock generator.....

Note that on Ultra there is a Genlock Output that can be sent out to the cameras.....You will have to review the sony manuals to find out if they will accept BB or TriLevel for 1080i operation...Note if they do not have Loop through for the genlock then you will need to have an Analog Video DA to distribute the genlock to all of the devices that need it.