[alanw]

I had similar screen problems a few times. First thing I'd do is reset the unit to factory defaults. Get it working that way first, then you can tweak the manual settings to your liking.

First time I had the problems was due to air gaps in my goop, confirmed by pouring some water on the transducer which cleared up the signal. Re-gooped it and it's working good.

I'd say it's most likely transducer mounting or wiring problems. Having the same problems with a second head unit pretty much confirms this. Did you try a new transducer with the new unit?