If an RCA input on a piece of electronic gear such as an amplifier or CD player is no longer outputting signal to the device it is connected to, it's likely the RCA input is broken. In most cases this fault has occurred because one of the wires connected to the RCA input has become detached. In many cases this can be fixed.
Unplug the device from its power source.
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Turn the device over onto the top and examine the bottom panel for screws. Loosen and remove the screws and remove the bottom panel to access the interior of the device. In some cases you may need to remove screws on the side of the device and pull off the outer upper cover as well.
Examine the two wires leading to the RCA input. If one of the wires is detached or frayed, you should be able to fix it.
If the wire is frayed, cut out the frayed section, then remove 1/4 inch of insulation back from the cut.
Hold the bare end of the wire against the tab on the back of the RCA input that it came off of. Identify this from the absence of a wire and traces of wire or solder on the tab. Apply the hot tip of a soldering iron against the wire end and the tab until it's hot, then touch the end of your solder to the joint until solder flows into the junction.
Remove the soldering iron and let the solder cool. Replace the covers of the device and plug it back into its power source.