OK, well, your amp is working but not passing signal on one channel. What you want to do is to download a 60Hz tone or download a signal generator onto our phone, then put 60Hz signal into your amplifier. Set your meter to AC volts (the 2V or 5V scale is good to start with, if you have an autoranging meter, this doesn't apply). Now with the tone playing, measure the AC voltage between ground and each center pin of each RCA jack.
Next, turn the volume pot all the way up and measure the AC voltage between the center lug of each level of the volume pot and ground.
Let us know what these voltages are. Do also note that these two tests can be done with the amplifier powered off.
-PB