Update, Dave,
There is a possibility that the SC board will cause code 3 - it can cause codes 3,4,5,6,7 or 10. However, you can isolate the A board to the point where it will operate on it's own although in effect the set will not function, the A board will still be active.
Unplug SC2 and SC20 on the SC board, SS11 on the SS board, P35 on the P board and the 3 flat white flexies on the A board.
Power the tv on. If you still get a blink code, the A board is the prime suspect.
Bruce