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Friday 11 May 2018 at 13:57
Swap the left and right opto boards (the ones that are actuated by pushing the flipper buttons). These can get dirty but more often are failing these days.
Swapping them will change the fault to the other side if it is the board dying.
Source: http://pinside.com/pinball/forum/topic/flipper-loses-power#post-4392022