hifi engine

Marantz SR225 Reciever... no sound 1 channel

Hello, i recently garbage picked an old Marantz SR225 receiver (and matching speakers). I plugged it in and it powers up, all lights come on. I get sound out of the right channel but not the left. I tried flipping the rca's around, still only sound on the right channel. This tells me that from the cd player to the reciever is okay. I flip flopped the speakers, again, only sound out of the right side. So the speakers are both good. I tried plugging the cd player into the other inputs. Aux, phono, and tape in. I still could only get sound out of the right side. Does this sound like a problem in the power amp section? or do the inputs go to the switch and then the pre amp, meaning it could also be in the pre amp? Does anybody know a common problem that causes this? should i look for anything like blown resistors or caps in certain places? anybody got a service manual? I would love to use this to power my small monitors in my studio. Thanks!