Yes, the outputs, one or the other on the affected side is open in such a
way that allows the driver to power the output. The driver will pass
enough current to operate the headphones, but not the speakers... which
quickly clip the output of the driver. Check the outputs with a vom and
you'll find one of them open. Replace in pairs, adjust bias, and offset
voltage measured at speaker outputs. Check associated resisters for
opens. Power up with variac, watch current rise at low voltage to ensure
everything is good before applying full line voltage.