I would be checking/eliminating.
Power supply associated with analog input channels, check voltages and stability with scope.
This all might be useless given that HDMI is working... but it doesn't look like Dave is following the first few commandments of electronics repair:
1) Thou shalt check voltages
0) Is it plugged in (I think he got that one
-1) Can I trust my tools ( e.g. does my equipment generate good video signals ... which might not be the case for the wonky box that showed the on screen menu)
If the problem is the missing surface mount component someone else noticed, then I suspect rule 1 would have shown something interesting.