Symptoms are similar to what I've seen before, but never got an error. Surprised you didn't find a bad FET. Double check the FETs in this post I made about fixing the 406. Fixing 406duo In my case, the resistor driving the gate of the mosfet was bad. You should check that as well. For the right side mosfet the gate pin is the top pin. Trace that pin and you should find a resistor. Compare it's resistance against the same one on channel 1. I don't remember what it's supposed to be.