Hi Ken, the capacitors are black with white line, white being negative and are installed correctly.
Setting the DVM at 200MOhms I get 15.4 one way and 0.6 the other.
The diodes D4 and D5 have 3 scribed lines one end, both of which have the lines on the VM side. Closest to the "D" on each.
No visible signs of shorts or dodgy soldering anywhere on the board.
At a bit of a loss as to what the issue is, I think I'll just remove the regulator and flash the firmware to see what happens.
Thanks for the help, Mark.