I bought an old DPL receiver to use with my main receiver for Dolby Digital Es and DTS EX. The problem I'm having with the old receiver is that no sound comes out of the 'Mains' even when I do 'test tones'. All the other speaker terminals work except for main L and R. When I hit the button for different sources I hear a 'click'. And when i turn up the Volume all the way I hear hiss. I also tried using other inputs as well. What else can I check. I opened up the case and the fuses all look ok. I have a volt meter but wouldn't know what to check. Please help! Thx M F.