Originally written and posted 2 June 2001.
Content last modified Saturday, 2 March 2019 .
External links last verified Friday, 8 June 2016.

CP290 home control interface

CP290 Home Automation Interface

There has been a great deal written about the CP290, including modifications to improve clock timekeeping and the like. It used to be possible to visit the Home Automation Knowledge Base (Dead Link, remaining here in case it gets revived, and for archive searching) and ferret around there for most, if not all, of this useful information compiled by fellow X10ers. Sadly, with the demise of that site, you’ll have to do your own searching.

This page covers what i have to add to (or reiterate regarding) the CP290 saga.


This probably came from Ido Bartana’s site. Found it in my collection and it’s small enough to make available here.

Please Please Please download the following PDF file rather than repeatedly viewing it from this site (if your device supports downloading)! (This should happen automatically in most cases as long as you/your device and software are not doing anything to override forced downloads.) This will help keep my WWW hosting costs low, allowing me to keep this site free and ad-free and donation request free. Thank you!

CP290 schematic (PDF download)

Repair: Not Controlling Modules

Does your CP290 look like it’s happily sending out signals as usual (per its red LED), but nothing’s being controlled, or control is wildly intermittent, and you’ve eliminated powerline interference/weak signal issues as the source? I had this happen, more than once. One time, the CP290 suddenly stopped controlling anything, even modules plugged into the same duplex receptacle with it—total failure. Another time it was the same deal, except intermittently, sometimes it would work once in awhile.

Insufficient or No PLC Signal

Basic signal tracing showed that the PLC signal was OK on the collector of TR5, but not TR3. TR3 2SD667 had failed. Replacing it restored reliable operation.

PLC Signal Present, But Still Not Controlling

This was the case where once in awhile it still randomly worked. Things got even weirder when i looked at the PLC waveform: it was nice and strong and solid. What the heck was going on?!

By chance, when viewing the PLC waveform on the powerline kinda sorta sine wave, i noticed that the PLC signal was shifting its position on the A.C. waveform. Studying the schematic (CP290-3.pdf), i noticed a whole bit of extra circuitry not existing in most X10 controllers, with a connection labeled LSYNC. Studying the circuit—TR1, IC3, etc. etc.—i could see that this was a Line Sync signal output. Then i noticed that the C3 100µF 25V electrolytic capacitor was doing a lot of filtering to make some D.C. Put my sillyscope across it, and saw a lot of ugly unfiltered nastiness. This unfiltered noise was messing with the timing of the LSYNC signal, making it crawl all over the A.C. waveform instead of being where it was supposed to be. Replacing C3 very nicely cleaned up the waveform across it to something much closer to D.C., put the PLC signal back stably where it belonged on the A.C. waveform, and resolved the issue.

CP290 Alignment

To ensure successful alignment, please be sure to read important information common to all X10 alignment procedures before proceeding.

CPU Frequency Adjustment

I do not know what effect this would have on any external function, therefore i found no reason to adjust TC3, and left it as-shipped from the factory.

PLC Frequency Adjustment

  1. Unplug CP290 and remove the 3 under-foot screws and the one in the battery compartment holding the two body halves together.
  2. Position the unit in a fashion which allows easy adjustment of the two transformers which will be adjusted.
  3. Connect frequency counter to powerline signal sensor (not CP290). Power up counter and signal sensor, allow counter to stabilize.
  4. Short transistor TR5 base to emitter to allow the 120kHz oscillator to free-run.
  5. Connect CP290 to A.C. line.
  6. Adjust transformer TC2 for 120kHz.
  7. Unplug the CP290, powerline signal sensor, and disconnect the frequency counter. Leave the free-run short circuit in place.

PLC Output Amplitude Adjustment

  1. Move the CP290 to the location where it will be used. Bring along oscilloscope and powerline signal sensor; connect these to a separate circuit, or at least an electrically distant outlet on the same circuit.
  2. Set up oscilloscope and powerline signal sensor to monitor the A.C. line.
  3. Connect CP290 directly to the A.C. line.
  4. Adjust transformer TC1 for maximum 120kHz signal amplitude. This is likely to be a broad, “low-Q” peak.
  5. Unplug/disconnect all. Remove the B-E short on TR5.
  6. Connect CP290 to computer and A.C. line. Run self-test. Reload programming. Test for normal operation.
  7. Unplug and reassemble CP290.
Questions/comments may be addressed to: Sonic Purity