Can you get a pic of your boards and connections/connectors

Also a pic of the left flipper wiring on the coil lugs for the lower and upper playfield from underneath?

Those are the places I would look first.

I just took a look at the boards. There are a lot of jumpers on the MPU. I would first make sure those jumpers are in the correct positions for a System 7 configuration.

How does your PSU look?

Lots of connections in the path for the flippers on this game. Make sure they are all clean, in good condition and connected properly.

Check the contacts on the cabinet switches. If the game hasn’t been played in a while they can get oxidized and need a little sanding to come back to life.

Check to see if the flippers stay up when assisted. If they do, check the eos on the flipper mech.

First thing I would do is check the power supply. make sure its working properly
test the voltage
replace any old capacitors, or better yet just replace them all