Quoted from Quench:

Which Pop Bumper is it?
Was/is the diode on the coil measuring good?
On the SDB, it might be a faulty U3 transistor array or the 74L154 causing the transistor driving the Pop Bumper to lock on.

Quoted from Quench:

Disconnect the J5 connector from the Solenoid Driver Board (SDB) which will disconnect that Pop Bumper so you no longer blow the playfield fuse.
Measure the voltages on the SDB at:
a) Pin 14 of U2 (74L154)
b) Pin 10 of U3 (CA-3081)
c) Pin 9 of U3 (CA-3081)
d) The banded side of diode CR12 (near transistor Q12)
Report back your measurements.

Quoted from Quench:

U3 is a transistor array. The voltage measured on pin 10 of U3 (base pin of a transistor within the array) is excessively high most likely because pin 10 has internally gone open circuit. This is resulting in pin 9 of U3 (collector pin of the same transistor within the array) to be pulled high which is always activating the Q12 transistor down stream and locking on the Pop Bumper solenoid.
Normally, when the solenoid is not being selected to activate, pin 10 will sit at its highest level of around 0.8 volts and pin 9 should be near zero volts which leaves transistor Q12 switched off.
Replace the CA-3081 device at U3.
If you're really really desperate to get it going while you wait for replacement parts, you can temporarily swap U3 with the CA-3081 at U4. U4 is not driving any solenoids with that faulty transistor within the array. Just keep your fingers crossed no other transistors within the U3 array are faulty if you do this...
Good luck!

Quoted from Quench:

U3 is a transistor array. The voltage measured on pin 10 of U3 (base pin of a transistor within the array) is excessively high most likely because pin 10 has internally gone open circuit. This is resulting in pin 9 of U3 (collector pin of the same transistor within the array) to be pulled high which is always activating the Q12 transistor down stream and locking on the Pop Bumper solenoid.
Normally, when the solenoid is not being selected to activate, pin 10 will sit at its highest level of around 0.8 volts and pin 9 should be near zero volts which leaves transistor Q12 switched off.
Replace the CA-3081 device at U3.
If you're really really desperate to get it going while you wait for replacement parts, you can temporarily swap U3 with the CA-3081 at U4. U4 is not driving any solenoids with that faulty transistor within the array. Just keep your fingers crossed no other transistors within the U3 array are faulty if you do this...
Good luck!

Quoted from Quench:

Looks like you've got an issue in the switch matrix.
Can you remove all balls from the game and make sure all drop targets are raised.
Go to switch test mode.
Does it report "0" in the Ball in play display?
When you activate the lower pop bumper switch with your finger does the game report 18 or 19 in the player displays?
And what number is displayed when you activate the left pop bumper switch with your finger?

Quoted from Quench:

Ok if you've got the manual, go to the switch test number page 17 and activate each switch one at a time starting from switch #40 working backwards to switch #01 (it's important you do it backwards).
Report back the details of which switches are reporting the wrong number in the switch test.

Quoted from Quench:

No. The chip at U3 on the SDB is completely unrelated to the switches.
You've got a short between switch return line "I2 and "I1" shown circled in red below.
Firstly, make sure the three coin slot switches on the coin door are in the open position and not stuck closed.
Check the capacitors circled in green on the switches shown below and make sure they aren't short circuited.
Then check the diodes circled in blue on those switches, again looking for any that are shorted.
Let us know what you find.
.