The board in the top right corner with the two heatsinks is the solenoid driver board. Rectifier board, sometimes called power supply, is in the bottom right corner, above the transformer.

You didn't mention which board you were testing voltages on. Every board in the game has test points. Link below should get you pointed in the right direction. If you don't have a game manual, you can download one at the second link.

https://www.pinwiki.com/wiki/index.php/Bally/Stern#MPU_boot_issues
(note the reset section in the link)

https://ipdb.org/