Hi guys - thanks for all the responses, again, and yes, the problem did turn out to be the radio that I soldered back together (sheepish )! Hey, it worked for almost a year! I think I must have overlooked a connection that should have been bridged, and worked it's way loose over time - the antenna is supported by the (cracked) circuit board, and as I would move the transmitter around, the antenna became a big lever, flexing the circuit board more and more.
It finally dawned on me that I could just pop the crystal into my good radio to check it. I couldn't pick up the signal with the O-scope. The broken radio worked okay up to six feet away from the planes, and then, moving just a little bit more, sent the servos into wild spasms, on two airplanes. The good radio kept both planes quiet.
So, I'm in the market for another radio. As I said, my son would like to buddy-box with me now, so I'd like to just pick up another Laser 4, but can anyone tell me how buddy-boxing works? Specfically:
In the student-teacher relationship, whose radio is actually doing the transmitting?
Must both radios have the same frequency crystal?
Must both radios even be turned on?
I believe I have a cable that will actually work - it's a nine-pin printer cable that I used on a Commodore-64 (remember those?) in the eighties!
Thanks again, Dan.