I have been trying to get output from my 2252 Marantz receiver. This unit came from the factory without any jumper between the "pre out" and the "Main In". Just four RCA jacks. When I hook up to the "Pre Out" jack I don't get any signal. My research shows a "internal" jumper - that seems to be some type of mechanical switch that is engaged when an RCA plug is inserted into the Pre Out. My question is do BOTH the "pre out" and the "main in" jacks require an RCA plug inserted BEFORE there is any output on the "Pre Out"? Is there a common failure modality associated with using the "Pre Out" on this unit? I doubt if the "Pre Out" has ever been used on this receiver. Could the mechanical switch - assuming that such is inside the component - have failed over the 43 years since its manufacture? Could this switch have "grown" together over time due to the constant passage of current? Help is greatly appreciated.