identify infrared receiver
After looking at the manual for 10 seconds, it is extremely unlikely that the IR receiver is broken, and if it is, there might be something else broken as well. 

First, check the remote selector switch behind the unit, verify that it is in SINGLE position, maybe flip it to SYSTEM position and back to make sure it will end up in SINGLE position.

Second, make sure there is nothing connected to the RCA jacks called REMOTE. If there has been some accidental audio connections to REMOTE jacks, there might be something broken inside. 

Only then, with an oscilloscope or logic analyser, verify that the IR receiver really is broken. If it receives just fine, then something else is broken.