It is considered good form to post a drawing and an accurate description of the problem. That having been said for the sake of saying it... If both channels are inoperative then It's likely the problem is in the power supply. If one channel is blown the chances are that you have an identical, hopefully ok resistor in the other 'working? (You didn't state...) Channel. I have had occasion to service many of those devices over the years. Typically the "Amplifier" will have 2, 25 to 500? watt amplifiers and some means of isolating the dc input and increasing it's voltage, usually a power oscillator and transformer or power multivibrator of some kind and generally it's the Power Supply that fails. Some investigative work with a DMM should straightaway put you on to the bad parts, a slightly scorched smell may well be present too and is a good indicator of parts that have been stressed..
Bob