Surely we are talkking J3 on the solenoid board here - top right hand .1 connector.  If things blow with just J1 or J2 connected you have serious problems!!

BTW, U1,3 and 4 are not strictly IC's, they are transistors in an IC package, hence my comment on testing them with the diode function.  I have never seen U2 go bad, but I guess anything can happen in pinball.

Looking at Q3, I would say the knocker coil is cooked!!  Go through everything methodically on the weekend if you have time.

cheers
Ian