Do you have voltage present at the flipper coils? Are the EOS Switches making good contact. You can test the flippers like any other coil if the voltage is present. Ground the center tab on the coil momentarily to see if the plunger pulls in. The correct tab to ground is the one with only a single wire going to the EOS switch.

How are the connectors on the rectifier board? All power originates and returns here. Anything wrong here will keep something from working

Next thing I would test is continuity from the relay pins 8 & 9 to pins 2 & 1 on connector J2 on the driver board and relay pins 4 & 3 to pins 8 & 9 on connector J1. This is the path of the flipper power but would not prevent the relay from operating.

If you pull the SDB you'll see the traces near the relay. They're pretty straightforward. If this is an issue it's probably cracked solder joints.

p.s did you check the eos's? If they are not connected the hold coil doesn't have enough pull to pull in the flipper plunger. you can temporarily jumper across the switch to eliminate it as a problem. Don't leave the jumper though or you will melt the flipper coil quickly

If you pull the 3081 and test it do the readings go back to normal?

Also I'm no expert but it looks to me like you can test the flipper relay by applying ground to J4 pin 8. That would test the whole circuit

Corrected, thanks for catching that!

It looks like the disable line goes from mpu j4-7 to sdb j4-8 and the color of the wire is blue white

Assuming you have a Bally mpu and not an altek, swap the 2 Pia's and see what it does