Check the coil to see if it has right ohm value, then check the related transistors on the driver or on the small playfield. Gottlieb ran out of drivers and put transistors under the playfield to run some coils.

Can you post your wiring? I assume the pop board tests good if you swap it with another?

check your driver board. You more than likely have a bad transistor. very common but meter the coil first to make sure its not the reason it blew in the first place.

Isn't the point of the pop bumper mod that it can't lock on?

2 things happened
1. The coil diode shorted out. I am assuming it is the correct coil winding here. As it was probably working until it did not work.

Replacing, retrofitting to the pop bumper coil is 100 percent the right thing here.

Next problem.
When you turned the game on with the retrofit and a blown diode in the coil I bet you blew the transistor on the new pop bumper board. So this will also be bad. I have done the same exact thing here.

So, change the diode or entire coil and also repair or replace the pop bumper board. Ones from Rottendog will work