I'd take a step back and start with the basics. Remove J1 and J3 from the Rectifier board. Switch the game on and check each voltage at the test points.
Then add J3 - The game should not be tripping the safety switch
If you have got this far without tripping the RCD, then it will be a coil or something on the Solenoid Driver board. Install J1, and it will trip.
I would remove the connector to the relay mounted on the transformer board. This eliminates one problematic output from the SD board.
You could try to isolate the coil / transistor / CA3081 (as Ken suggested) by removing connectors from the SD board and switching the game on. With all connectors fitted, this is the breakdown of the Transistor outputs by connector on the SD board;
J1
Lower Right thumper
J2
Left Flipper Button
Right Flipper Button
Coin Lockout
Left Sling
Right Sling
Tp Thumper
DR Target reset
Knocker
Ball Kicker
J5
Saucer
DT Red
DT Blue
Outhole
Lower Left Tumper
DT Yellow
DT Black
GI Illumination Relay
Switch the game off. Remove all connectors (J1, J2 and J5) - switch on. Nothing should happen. Switch off. Add one connector at a time until it blows the fuse. Then you have isolated the problem to one connector with the culprit being one of the coils or CA3081.
I'd suggest one of the small coils in the drop target assembly is shorted against something or the DT reset coil is the problem. But the GI relay can also cause issues.
