A few other things: Check the power fuse on the bad speaker. It might be bad, or not in tight. Also, there is a little IC chip on the main PC board inside the electronics chassis which sometimes fails, producing the problem you describe. Take the top off the electronics box, (DON'T TOUCH ANYTHING!) and check to see if the little LED on the circuit board is glowing. If it's not, then the IC chip has gone bye bye! Jim Power at ML will send you new ones, but they're only a couple bucks at your local electronics supply store. If you think that might be it, let me know and I'll try and help you further.
Neil