Thanks MM,

Unfortunately I don't think that will help...I'm 90% sure I've isolated it to the board, without connectors plugged in.  I will replace U20, which according to PinRepairs is the most common fault with these...
I've come across some further batt damage (far right batt had let go)...I've cleaned and re-flowed what I can and buzzed out what I can.  I'll replace the U20 and see how it goes...I don't want intermittant faults, so I may look at a Rottendog replacement, if they can be sourced locally happy days!