I have, many times, taken a line feed fron a sound board into my Z-1 (selected line vs. mic) and everything is great. The other day, I was feeding a line feed into an HPX 370 (line feed also selected on camera) but couldnt hear anything. After several songs, I switched the camera to Mic and it sounded fine.
Why would this happen? I also have used Sennheiser wireless transmitters to send this to a camera and was forced to use mic level.
I was wondering when I come off a soundboard, isn't that ALWAYS a line feed?
It depends on what board and where on the board the feed was coming from. As you sumised almost all board feeds are line level except when they're not. Always test any feed to be sure you're set up correctly.
Most wireless transmitters are designed for mic level inputs and aren't padded down enough to handle a line level feed. You can get 50db plug in pads (xlr-xlr) that will make a line feed into a mic level feed. Always good to have a couple of them in your kit.
Were you monitoring the audio directly from the camera or did you have another device hooked up to it that you tapped off of?
Also, did you check the input levels to see what they were set to? There are separate controls for each input, front and rear. Whichever one you used, you'd want it set to "Man" so that you have control over the gain.
Apparently the user can choose between 18dB and 20dB of headroom, so the top of the scale (0dBFS) for this camera probably equates to +22dBu or +24dBu. The middle bar is -18dBFS or -20dBFS depending on your settings.