TECH Help: Secret Sevice lockup diagnosis

[eCobb pinball]

This Secret Service has operated flawlessly for years. Yesterday on powerup it lights up and audio amp fires, but then everything freezes. Does not enter diagnosis or startup test routine. No response to switches. No CPU Power-on led lights. No battery leakage or board damage.

Before I begin the task of pulling/testing fuses, etc, etc, does anyone have a suggestion on a likely culprit and starting point?

Thanks!