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I can find no source for a schematic for the FCV382, I regret to say, after a search for a source.
To find any sort of manual, it might help if I knew what the specific sub-model of your Furuno is.
There's these, for instance:
and so forth.
Which of these is your model, please?
If no source of the schematic or repair information is available specifically for your model, then you may need to go on general principles:
A. if the display is rolling, the vertical rate may need adjustment. Look for an adjustement trim-pot. Try it - with a note on the original position, since if it's the horizontal trim-pot instead, the results would be not good at all.
B. if there are no trimpots, then you may need to replace components in a directed sort of random order: components that look defective, that have overheated spots on the board under them, etc.
Let me know the full model and submodel # ***** I will search further.