C80 screen sometimes not working

[speakrdude]

When I received the boat, this March, the c80 came on fine, but the radar wasn't turning. Disassembled, lubed up the motor, now it works.
But now, sometimes, when I turn on the c80, The screen only shows a couple of white vertical lines or a slowly black burst looking screen.
Sometimes, It comes on and displays fine.
Is this a maintenance item, on perhaps a ribbon cable?
I hate to spend very much on this type of repair, as I boat on a reservoir in NW Arkansas, and there's not much need for a radar.
Thanks,
Jim