Funny timing on this post. Last night I looked out the window at my megatree and noticed that one string of lights was "stuck" on. I have been using Vixen in timer mode and the sequence had shut down for the night so I thought it might have been a glitch. I ran the sequence manually and that string would not blink off. Went outside and opened the box and noticed the indicator LED for that channel was OFF even though the light string was lit. Pressed the reset button on the board but that didn't help. Ran the test and all the lights turned on, but that channel never went out. Pulled the plug, waited a bit, then plugged it in and that channel still stayed lit. Oh and the LED for that channel responded exactly as it should have. Lit when I expected it to and turned off when it was supposed to.
So I suspect that it is a bad triac. I'm going to pull the box in and do some testing. It has been rather damp lately, but the board looked dry and I had sprayed it with CorrosionX last year when I put the board into service.