Constant flipper shut down freeze

[GospelforHostiles]

My 1980 Black Knight machine will freeze whenever the flipper are constantly activated for 3 seconds. It remains light up and can start over again as if nothing has happened......until the flippers are used nonstop for 3-4 seconds. Any suggestions?

 

[lukewells]

Bad filter capacitor on the PSU
or bad ground between head and body
or bad connection between PSU and CPU board

Measure voltage at the CPU board while flipping, and also check for AC ripple at the CPU board, even easier if you have a scope