hi you might have a shorted tvs diode on the out out side take cover off and check 4 diodes there is one on each channel output, disconnect one end and check continuity if 0 ohms diode is shorted and needs replaced, your track short frequently causes these diodes to short! if you disconcert and find the shorted one while disconnected power up and you'll probably find tiu now works, you don't want to operate it like this but is ok for a test! if you need repaired let me know!
Alan