A follow up post to the problem I described.
I received several replies offering solutions since the post went live. One of them, from Mr Quek, a genius in my opinion, suggested I plug the board back and try again. He seemed to be confident of some loose connections causing the problem. I did try to fiddle around with the connectors the night I dismantled the circuit board. But you know what? He is right!!! That confirmed that he is indeed a genius!
Thank you, Mr Quek!