There's not much detail in your fault description.
First check that the Balance control is centered.
Then you need to do some simple fault-finding.
On the back of the tuner/amp, swap the speakers over, so the L output goes to the R speaker and vice versa. If the same speaker is silent, the fault is in that speaker or the wire from it. If the previously silent speaker is now working, and vice versa, the problem is in the tuner/amp.
There are many possible reasons for one channel being dead in the amplifier and you may want to take it to a repair shop or replace it. If you want to try to fix it, email me at kris at heidenstrom dot gen dot nz and I'll try to help.
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