It is simple to see if it is the board - connect J3 only on the SDB.  This means there is NO connection between the playfield and the board, so if it blows the transistors, you know it is the board.  The small target dropping coils are notorious for shorting, so check that closely.

Thanks Bally, did that after inserting Q3 only powered up, powered off then tested transistor....all Good!
So i connected remaining connectors, powered up and no locked on coils.

I ended up changing over the U2 IC on the SDB last night, so this has potentially fixed the issue... i'll keep working through later tonight

A side note - no sound is audible, another dead board??? will see...