After working for years, my X10 stopped working.
After much unsuccessful trouble-shooting, I connected an oscilloscope to the 110v line, and noticed that there was another signal on the power line at about the exact same time as the X10 signal would be (the other signal was less than half the X10 signal).
With an able assistant watching the oscilloscope, and me at the fuse panel, I first removed fuses one at a time until the interfering signal went away, and then I put that fuse back in and unplugged devices on that circuit until I found that the power transformer for an external USB hard drive was causing the problem. The USB drive had been connected for over a year, and continues to work properly, but for some reason a few months ago, something changed in its power supply that caused it to put noise onto the power line, and mess up the X10 throughout the house (the wall transmitters would not send any signal, and using a simple wired transmitter would sometimes work, other times the wrong X10 device would switch).
The external USB hard drive is a 200 Gbyte Kaser bought at Costco a year or two ago. Its power supply is an in-line (not wall-mount) unit that simply says "Power Supply, model JHS-E02AB02", and has both a 5 and 12 volt output, each at 2 amps.
Update: Now I've also determined that our Nintendo Gamecube power supply prevents any wall switch on the same circuit from working (but it isn't nearly as bad as the above problem). I've ordered some X10 XPPF plug-in line filters, and will see if they keep the electrical noise away from the rest of the house.
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Topic: Interfering Power Transformer (Read 2953 times)