Quoted from chinosts:So no luck with replacing the 2N4401 .. my next best is testing the 7402 to see if there is an issue.. any ideas the best way I can do that? I can easily check to see if it's getting power.. but what about if it's sending any signal from pin 4? If I use my dmm by putting black lead to ground and red on pin 4 and just loop the test for that coil do you think that would be a conclusive test? Or even a test at all? My friend St work suggested putting 5v on the circuit after the chip and see if the coil fires.. that way you can rule out it being the 7402.. what would be the easiest way to do that without risking frying my system board?
You can often test these ICs similarly to how you test transistors with the DMM diode test: http://www.pinwiki.com/wiki/index.php?title=General#Testing_an_integrated_circuit
I've done the 5V thing before, just took a wire and tapped it on the leg briefly, but I try to avoid sticking live wires into the board when possible.
I'm not sure if you can pick up the pulse from the pin with your DMM, but it's an easy check and definitely worth a shot. An important thing when trying to debug problems like this is that the whole driver section is just the same circuit repeated many times. The 7402 controls multiple pre-drivers, so if you know one of those other solenoids still fires, you can compare your readings on pin 4 with one of the other pins that goes to another pre-driver when that one fires. If you can pick up the pulse to one of those, but not on pin 4, you know there's a problem.
The King's chamber kicker is Q75, which is also controlled by U45, pin 13. Get that one firing repeatedly in test, put your DMM on the pin, see if you get any reading. If so, check pin 4 while firing the kicker, you should get the same reading.
Note however that the problem could be farther back than U45. If you're not getting a signal on the outputs that you know you should be (because you can see it on pin 13, etc), then it could be that U45 isn't getting its input signal (pins 5 and 6). Again, you'll want to try to compare the signals going into 5+6 with the signals going into 12+11. If the input signals are the same, and the outputs are different, then you know it's U45 that's the problem.