So whatever digits are blank when you turn the game on will stay blank no matter what you do to the game?

Do the playfield inserts go into attract mode? Will it start a game and seem to play normally?

What work have you done to the MPU board and driver boards?

if the game plays, does the master display digits advance for the ball in play?

Do you have a logic probe?

Good info.

Plugging in a known good MDB is a great next step. You don't need to wait for the power supply rebuild.

I would replace all the header pins on the power supply when you rebuild it. As a short term workaround, you should at least reflow the solder to each and every pin.

Does the other set of digits on the MDB show the ball in play number and increment as it should? If your friend's known good MDB works in your game, I would replace IC2 and IC3 on your MDB.

Yes, the left bridge rectifier is for the solenoids. You can't measure AC on the red wires in reference to ground. Put your meter on AC and touch one lead to each of the red wires. That will tell you the AC input voltage.

If you have 36V DC at the + double wire side, the problem is not the bridge rectifier. Suspect J1 and J3 on the power supply board. Inspect both for burned or tarnished connectors and cold solder joints. Cold solder joints are very common on these boards and replacing the header pins or at least re-flowing solder on the pins is mandatory (as suggested in my post above). DO NOT waste your time chasing problems until your have at least re-flowed solder to all the pins on J1 through J6 on the power board.

Your repair person that checked your MPU and Driver board should have done the same to those boards. If not, reflow solder on them as well and find another repair person

Do the same to the sound board. Cold solder joints there could stop the sound board from working.

Whatever you measure on the red wires with the meter set to DC is not valid or helpful. Those wires come from the transformer and carry AC. To to properly measure their voltage, you need to set the meter to AC and put one probe on the lugs for each of the red wires.

In any event, if you are getting 36V DC on the + lead, you know the bridge is OK.

Good progress! Now re-flow the solder on the header pins of the MPU and driver board!

Meter on AC - one lead on the top red wire, the other lead on the bottom red wire. You cannot measure AC in reference to ground in this circuit.

Did what coil voltage are you getting with your friend's power supply board?

When you rebuild the power supply board, take each fuse out, and brighten each metal end with a scothch brite pad or similar. Also brighten the fuse clips. Make sure the clips grip the fuses tightly (they can lose their spring over the years).