Yellowing leaves on Onciduim?

[greenpassion]

I am almost sure that the orchid in question is an oncidium. That said, I think I may have a problem. Several leaves have begun to yellow. I don't think they're new leaves, which is a good sign, but I worry I'm doing something wrong. I repotted it in a good mix made for oncidiums, and have it under LED 60 diode grow lights, on a humidity tray. (I don't have window light) Am I overwatering it? I think oncidiums like more water than phals, but I'm wary of sticking something down into the pot to check for moisture-I'm afraid I'll hurt the roots!