Diagnosing and Repairing X-10 modules

Home automation today is full of choices, INSTEON, Z-wave, ZigBee, and more. Before all the wireless and hybrid protocols, the only choice was X10. Made popular through BSR and Radio Shack offerings, X10 goes back to the mid-1970s as a way to control dozens of lights and appliances over the power lines and then later via RF. When I bought my house, I replaced several of the wall switches with Radio Shack’s version of the WS467, where they worked for many years. Besides being able to turn lights on and off from distant rooms, it’s possible to set up a timer or send commands from a home computer. There are more options now, but when I began, the only computer interface was the CP290 which sported an RS-232 serial interface and came with software for a number of contemporary home computers. I bought mine with a disk and cable for the Commodore 64 and set it up to turn the lights on at dusk and off at bedtime.

Over time, though, some of the modules failed. I replaced some with new modules, others, I re-installed traditional toggle switches. Two, however, were problematic to replace: the living room ceiling light and the upstairs hallway light, because they are 3-way switches. X10 completely supports 3-way operation. There’s a specific switch model with a black, a blue, and a red pigtail wire, and a passive black-blue switch for the remote end. Unfortunately, the active end is somewhat less common and more expensive compared to a standard single-point light switch. What I recently learned, however, is there is very little difference internally between the two products.

The primary failure mode with my light switches was that the “local switch” on the front of the units stopped responding. You could only turn the light on and off from the remote switch or by sending commands. This was specifically a problem when coming home as the first thing you normally want to do is turn on the living room light at the switch by the front door. Recently, I finally decided to repair or replace the bad switches one way or another.

It didn’t take much of a search to find modification tips and schematics for the wall switch. The entry on "Replacing the Button" sounded exactly like the problem I was having. I pulled the old 3-way switch and popped it open.
15c8c30a_h When I got it completely apart, I could see exactly what the problem was. I had thought for years that a resistor had burned out or a cold solder joint opened or a capacitor failed. What really happened was a tiny metal leaf broke off and the button was no longer closing the local circuit.
For the quick fix, I have plenty of single-point switches and it was a simple matter to swap out the front plate with a broken contact with a working front plate. Down the road, a note on the schematic (confirmed by inspection of both circuit boards) reveals that the internal difference between a single-point and a 3-way module is two diodes, a resistor and a red wire, giving me a way to convert the common single-point switches into the uncommon 3-way variety. Even if my venerable CP-290 dies, I can whip up a modern interface with an Arduino and I’ll be able to keep my controls running for years to come.


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