On the bench with 2 power wires now soldered to the pads on the main board. This was quite easy using a magnifier because there were 3 pads for +VE and 3 for GND side by side so three times the area to solder to.Here's the XDA charging from the power supply and the power light turned yellow as well. It remains red with no battery, so I'm guessing you need a battery installed to make this thing work.Finally, here's a low shot to show the poor XDA is half naked, in fact it's backless and its guts were hanging out. Only the weight of the unit was keeping the battery in contact with the main board.
I managed to solder one of the RS232 wires on after this, but not the other one, it is very fiddly. I'll have a go tonight or tomorrow again and report back what happens.