[Boulevardier]

"..there is a pcb at right angles to the main board with several solder connections joining them."

I've come across problems with this type of connection with adjacent circuit boards - just close physical proximity, and use solder to bridge the gap! Always worth checking the tracks for good continuity. I always used to bridge the gap with scraps of wire soldered to each adjacent track.

Whatever happened to that "old-time" advice - "never rely on solder alone for a connection, make sure there is a sound physical electrical connection first, then "seal" it with solder"?