At the climax of his three-hour set, Springsteen and McCartney, backed by the E Street Band and Rage Against the Machine guitarist Tom Morello, played a storming rendition of “I Saw Her Standing There” to a rapturous crowd. Springsteen’s delight was palpable: He grinned throughout, his face lit up like a child with a super-sized Christmas gift. …

Then, at 10:40 p.m. local time, as Springsteen and McCartney were winding up the extended “Twist and Shout,” the sound suddenly dampened, and went quiet.

At first, the Boss didn’t seem to notice. He attempted to address the crowd, apparently unaware that they couldn’t hear him. But as it became clear that there was no amplification, he and lead guitarist Stevie Van Zandt played what looked to be a brief a cappella goodnight for the benefit of the front rows, shrugged, and left the stage.