Great !..... what did you do to fix it ?
Good question. I honestly have no idea.
I dismantled it a lot further than the brief looks I've had in the past. Everything inside seemed fine and there didn't seem to be any breaks in the circuits when tested with the multimeter.
When disassembling the boards have to be prised apart as there is a 26 pin (I think it was 26) connector which joined the top and bottom boards. The amp and output boards also had a connector card. I made sure these were very well seated when re assembling so I wonder if my son dropping it had just dislodged one (or both) of these. Would explain one channel working intermittently the other day when it hadn't previously.