The TFM-24/25/35 series have some well known issues with blown channels. But if you're getting good audio out of one and not the other, you can try swapping the speakers to make sure its not them, and double check your connections of course. It's possible the output relay on the left channel is flakey or defective - pretty sure those can be replaced. Nevertheless, if the amp hasn't been serviced, it should be. It's overdue.