Try exceriszing the connections for input and headphone jacks ( just be inserting qtr inch connector in/out of jack ) a few times. then plug back into your input. if that didn't solve anything while amp is on move the input jack around ( up, down, left, right, ) and see if this makes the signal cut in/out to normal playing. if so you just have broken solder connections on the jack. Also you may just want to test your Speaker to make sure no problems exise there. ( Voltmeter across + and - terminals ) prolly 8 ohms but will most likely state on woofer. if not of this fixes your problem let me know and i'll throw some more steps your way.