Unplug everything except the rectifier board. Start there. as Frunch says check the fuses for the correct value. Measure the test point voltages.
From there move on to the power supply. Plug only that board in and measure the voltages in and out. The PS appears to have the original large caps. I recommend replacing with a deluxe cap kit from BigDaddy that will have the correct format caps.

Once the power is nominal your ready for the MPU. Allech and B&I (Weebly) have good replacement MPUs. B&I is less expensive. I've used their MPU in my Power Play and it runs great. Altech is also very popular. I think that's the board Marco sells.

The Squawk and talk is the most finicky board. If it doesn't come up look for a pro to rebuild it. That board is just too rare for a newbie to touch and there is no replacement available. If you do not get sounds, try cranking the volume control posts back and forth before you panic.

Final tip, there is a rats nest of cables and connectors behind the displays. make sure they are all properly connected and the wires and colors match on both ends of the connector plugs.

Good luck. Post back with your progress.

Yes, IDC connectors are 'one-and-done' when it comes to the way they treat their wires. I avoid touching them unless there is a specific issue with them.