Check and see if BR2 is shorted. Plug in everything except CN3 on the power supply and see if it still blows.

The same goes for the PPB. Plug everything in except J7. Check for a shorted BR2. Also check Q1-Q5 for shorts.

Assuming everything is plugged in correctly (sorry, had to ask), pulling CN3 and J7 will take the load off of those two circuits effectively isolating the power supplies. If the fuses still blow then we have a problem in the power supplies. If the fuses don't blow then we have issues with the associated coils and drivers.

Report back and we'll go from there.

Measure the impedance on the J7 harness pins to ground. Let me know which one is low and we can trace it out. Pins 1,2,3 and 5 (Blk/Wht, Blk/Wht, Vio/Yel and Gry/Yel) are the 50V to the flippers and pins 8 and 9 (Yel/Vio) are the 50V A side. One of these will read considerably lower than the rest.

I assume the Red/Wht is pin 5 of CN3. Which pins are the two Red wires? Pin 6 should be the playfield 34V, pin 7 should loop over to CN7 pin 3, and pin 8 is listed as cabinet 34V. I don't see any cabinet circuits using that so I'm guessing it's pin 8 that is missing.

Based upon this I'm going to assume that one of the 34 volt coils or diodes is shorted and the associated driver transistor is probably bad. Pull CN19 on the MPU board and measure the impedance from pins 3,4,6,7,8, and 9 to ground. If a driver is shorted it will tell us which coil is bad. Do the same thing with CN12 pins 5,6 and 8.

If Q1 on the PPB was shorted, check the KickBack coil and diode.
This would also account for the F5 fuse on the PPB being blown.

Check Q1 again after the last test.
Chances are that it's toast again.

A Tech Chart might also help a bit.

Data_East_Last_Action_Hero_Tech_Chart.pdf

That's the power line for the Kickback.
Check if the wire doesn't make any contact with metal parts.

Correct.
Also check Q1 on the PPB.
Chances are it's blown again.

Coil diodes are always reverse biased meaning the cathode (stripe or band) should go to the side with the power. In this case the cathode would be toward the Vio/Yel wire.

Pull CN19 from the CPU. Does it still blow the fuse? If not then look at Q13, Q7 and associated components on the MPU. There's a 2.7k hold down resistor (R30) on the base of Q13 that may have opened up if Q13 was bad. Also look at the 68 ohm resistor at R18.

I'm just going off the schematic. I assume if all are 1.7k (brown-vio-red) instead of 2.7k (red-vio-red) it must have been a factory mod. I can't imagine any reason anyone would change them all out.

If it doesn't blow fuses or pull in the kicker with CN19 unplugged then my money is still on Q13 and/or Q7 but if they are good then your looking at the 7402 NOR Gate. Not really anything else to that circuit.

Did your MPU boartd have any battery damage/leakage?
Has it been cleaned the right way?
The 7402 is right under the battery.....
Just a thought....

I admit my TTL is a bit rusty but that doesn't make any sense at all. 7402 and 7408 are two different types of gates. The 7402 is a quad NOR and the 7408 is a quad AND. While they do share 2 truth table parameters the pin outs aren't even the same.

7402 (resized).png

7408 (resized).png