I'm having the same issues on my 550GZ random black screens. Sound still works. happens a few times every minute. Changed all my cables, still happening. I sent the recorder back to Noel Leeming who sent it to a service agent. They are charging me a service fee as they say there is nothing wrong with it.
Please note I have a new aerial setup with full signal strength, professionally installed.
Get in contact with Panasonic.