Originally written and posted Saturday, 2 March 2019.
Content last modified Saturday, 9 January 2021 .
The design of X10 circuits demand a great deal from electrolytic capacitors, especially those in power supply circuits of X10 devices lacking a power transformer, which is the majority of them. Always visually inspect all electrolytic capacitors in X10 devices having issues, and replace any with visual signs of trouble. Those with access to sillyscopes (oscilloscopes) may consider checking waveforms across various electrolytic capacitors in malfunctioning X10 devices, to see whether the waveform is reasonable or not.
It is well known that X10 systems suffer greatly from even small amounts of powerline interference, which is nearly ubiquitous in the post-1970s electrical environment. This page does not cover interference issues—they’re too complex and nuanced, and have been well-covered on other sites. Same thing for insufficient cross-phase coupling of X10 PLC signals.
This page covers situations where interference is not involved and powerline cross-phase coupling is irrelevant or known to be adequate. In other words: what had been a working X10 system with no changes (subtracting as well as adding) in terms of household electrical devices capable of altering X10 PLC signals (the vast majority of modern electronic devices, which is why legacy PLC systems like X10 have a bad reputation for reliability and are not especially popular for new installations).
Put another way, this page covers failures in X10 devices themselves, in a known-reliable home powerline environment.
I have seen this several times with an SD533 Sundowner mini-controller and once on a CP290 home control interface. Each time was a different failure. Always the indicator on the controller indicated that a signal was going out, when the actual signal was not what it was supposed to be, thus failed to control anything.
All sorts of failures may cause this. Here are ones i’ve seen:
This was a weird one i saw on my CP290. It only happens with more sophisticated controllers such as this model, which have circuitry dedicated to timing where on the A.C. waveform the X10 PLC signal will appear.
For right now i’ll refer you to my CP290 home control interface page. If i find in my own life or receive site correspondence from others that it’s a more general issue, i’ll rewrite and put it on this page.
Far and away the most likely scenario is that there is a new electrical device ripping electronic farts (e.g. putting out powerline noise and/or sucking 120 kHz PLC signals), or a device has been removed that has thrown off the electrical impedance on some circuit enough to degrade the PLC signal at the module.
I had one module which had worked well for years, then gradually became more and more unreliable, with no changes in the electrical environment. Alignment cured the problem. It was an old module and electronics do age. The amplitude of the PLC signal did not seem that low, however i was able to realign this standard lamp module’s PLC transformer for peak resonance and restore reliable operation.