Heres what I would try, but mind you, Im not nearly as tech savvy as most of these folks. Turn chassis plate upside down, keep hands, pets and kiddies clear. Poke around with a non conductive probe ... wooden chopstick or small diameter dowel rod works well. Not very technical but this is actually referred to as a chopstick test. No kidding. Just probe/poke/tap around the rca jack, volume pot, headphone jack and the associated wires and just about anywhere else if those components dont show the issue. You can do this when the right channel is working to try and get it to quit or generate noise or when it's out trying to get it to come back to life, even if just for a second. Could be as simple as a cold/poor solder joint, or wire broken underneath the insulation. This "test" can often point you in the right direction, or right to the source when you have an intermittent connection/problem. The good news is that there isnt much that can go wrong with the amp and since you built it, you can fix it. Just have to find it first. Stay persistent and again, be careful when poking around, keep bare fingers clear.
