Sorry for the delay.
I have isolated the problem, but it is needing a hardware redesign to correct it. This is taking time as a new PCB needs to be made.
I've got the 'problem' logic board and cables fitted into my Vectrex, so I'm working on it right now.
If you are having the 'messed up menu' problem on your console, I will need you to send me the cart back.
Thanks