It sure sounds like mpu issues, can you confirm the board is completely booted?

The gi is always on so we can ignore that. The 3 lamps locked on looks like a non-boot. Are you getting the right number of flashes on the mpu? Are the displays working? I'm assuming they are since you can get to lamp test.

The display driver board completes the path to ground for the lamps. By grounding the tabs of the scrs on the LDB while in lamp test mode the lamp should light. If this works it is clearly a mpu (or wiring) issue. How do the pins look? Shiny or dull? Same with the crimp ends in the connector.

The scrs are similar but are measured differently. Pinwiki talks about the differences. Being able to ground the tab (or the metal back) works the same though.

I had a stern nine ball that would only fire the bank reset and outhole solenoids and it did it every 10 seconds. It was a connector issue.