Unhook your lower left hand board and see if it boots and plays. Also double check your dip switches and make sure you have the proper game set up and that it's on free play.

It looks like either you or someone previous replaced all the connectors & contacts. This is likely your problem, or maybe the J3 on the power supply was not done or original. Dave explained to me in the past over voltage LED will be on due to low voltage as seen by your voltages. I would post pictures of transformer board! I see the power supply was done. Verify your power for 5v to driver & mpu, from the transformer. Guess you are missing something. Red wire #8 on top right side driver board is important.

looks like the 5v LED is not lit on the sdb/v-reg board but the 12v LED is lit. I'd take that to mean the 12v to 5v voltage regulator is not working or it is in a shutdown mode because over current (short circuit).

With just the top right connector on the driver board and rectifier board connectors on. MPU bot left unplugged, lamp driver top left unplugged, all display unplugged. Try to power on and see if the 5v LED comes on the driver board. If the 5v LED still does not come on the driver board regulator is not working or is still in a shutdown mode. At that point I'd think there is a problem with the SDB/V-Reg board or something is really wrong with the connector. Like one of the 5v pins at the top right plug of SDB/V-Reg board is swapped with ground when it was repinned.

Also the loop wire at the bottom of the top right solenoid harness can be a problem. So check all your wires are correct!

A circuit board likely has a short. You can use a DMM to check resistance from the 5v to ground test point on each board and see if any read 0 ohm or close to zero ohm.

Could also plug in one board at a time looking for the one that is dragging down the 5v.... but that can be kind of dangerous if the short clears it self with brute force... like a capacitor explodes.

i bet if you pull up on the long connector on your power supply board it will start to work....probably a bad solder joint on the pins....very common.....

His sdb 5v led lights up when he unplug most of the boards. That most likely means one board is causing the voltage regulator to go into shutdown mode because over current is detected.

It could be a connector pinned wrong, lamp driver or any display has a 5v short. The new replacement boards are likely fine.

Ahh.... yeah I did not even notice at first that you had the MPU justified to the top instead of the bottom. Must have had 5v touching the grounded mounting rails somewhere which made the regulator go into overcurrent shut down.

have fun