as you figure, your problem is somewhere on the main board / input board or the input itself. Since the main board is generating (internally) its menu and it looks ok, the board itself may be ok AT it "output stage"... but that doesn't rule out the input side of the board or the input board (assume seperate one) that things are connected to. You didn't answer what you are feeding things with. At the component level switch around leads and see if things change.
Basically, it would appear you lost the blue input for what ever reason. Disconnect the red from the component setup, screen should go green.
if you have access to rgb output device and a vga to rgb cable, you can readily "experiment" by switching around the components. Further, your problem "statement" didn't really specify what happened to cause the problem... eg. just happened, happened after long storage, happened after dropping, happened after cleaning, etc.
Still further, most boards have labelling on them to indicate things like voltages and such. Check to ensure those voltages are indeed present on / at all boards.
As for whether the tv is worth it... depends on whether you got something better to do...
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