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[toasterking]

I noticed something odd today.  If I click the switch on my firebox blower on and off a few times, an X10 UM506 Universal Module on a nearby outlet will invariably switch its relay OFF simultaneously when one of the toggles occurs.  The blower is a shaded pole motor and so it is a significant inductive load.  I haven't looked at the spike on a scope, but it's enough to cause the speakers in my Panasonic plasma TV to "pop" also.

It is strange to me that the Universal Module responds this way.  The Universal Module has a bistate relay with 2 coils, one to close the contacts and another to open them.  The coils are driven directly by the 110V AC input for a single half-cycle, switched by an output from the PIC.  It is curious to me that a spike from the blower motor will cause the Universal Module to activate the "off/open" relay coil but not the "on/closed" relay coil.  Also, it seems that the firmware in the PIC microcontroller in the Universal Module does not acknowledge that the module has changed to the OFF state, because if I have the switch on "Relay & Sounder," the module will continue beeping despite the relay contacts having opened.

I also have another X10 UM506 Universal Module in a different location with a similar problem.  Sometimes, but not always, the relay will close and then immediately open when sent on ON command.  If the switch is on "Relay & Sounder," the sounder continues beeping despite the relay being "off."  The contacts are not driving an inductive load; they are driving an input pin on another microcontroller.  I have tried replacing both of these Universal Modules and they all behave the same in their respective locations.  I have not checked the date codes on all of them but I should probably do that.

Long shot, but is anyone familiar with this problem and a potential solution?

[toasterking]

I should also mention that both of these behaviors persist regardless of whether the Universal Modules are set to Momentary or Continuous mode.

[dhouston]

Several years ago (when Usenet's comp.home.automation was still thriving) I had a similar problem with a socket rocket that would turn off when a standard wall switch turned an old fluorescent fixture on. While I never caught the spike on my 'scope, I could see arcing in the switch. Replacing the socket rocket with an LM14A solved my problem. Around the same time, there was a post to comp.home.automation about a similar problem with an X10 wall switch...
https://groups.google.com/forum/#!msg/comp.home.automation/HJOVTh8Y_Ps/6vX-Nood1GIJ  
You might find similar floating pins on the PICs controlling your Universal Modules.

Another possibility is the spikes are causing a momentary drop in line voltage sufficient to trigger the PIC's brownout function.

[Brian H]

Investigating the floating pins sounds like something you may want to look for.

I have seen similar reports on Smarthome X10 clones and Insteon modules.
Some users put a snubber network across the load and it corrected the issue.

[toasterking]

Both great ideas.  Thank you both for pointing these out!  I remember now about X10WTI's tradition of saving a few pennies per unit by leaving I/O pins floating.    I would usually blame the "local control" circuit first, but as the UM506 doesn't have one...

"Helpful" points from me.  I'll hopefully get around to doing this soon and will post back with results if/when I do!

[dave w]

Not directly related, but I have something (unknown identity so far) that when it changes state my WS800 X10 RF command receiver and Homeseer interprets as a "D All Off". My D house code is all accent lighting, so is not a big deal. I just can not pinpoint the RF source. But (for me) that is half the fun of X10 and home automation. 

[toasterking]

I finally opened one of my universal modules tonight to investigate.  This one is a PUM01 with date code 10F23.  Before opening it, I connected it in place of the UM506 in my first post and confirmed that it behaved the same way.
The initial inspection reveals that every pin of the MCU is connected.
The MCU is a Sonix SN8P2501BSB.  I found a datasheet, which I attached here, and a photo I took of the PCB.

I suspected it was possible that pin 13, which I thought was leading to the pad in the center of the OFF dome switch on the top right, was picking up a spike since it did not appear to be pulled up or down.  At the risk of disabling the button, I tried pulling pin 13 both up to Vdd pin 4, then down to Vss pin 11 with a 10KΩ resistor with no success.  It was then that I realized that the trace for pin 13 was actually leading to a transistor between the ON and OFF pushbutton switches at the top, which was in turn connected to the pads on both of them.

It also would not make sense that the MCU is picking up an errant OFF signal, because as I mentioned in my first post, the sounder does not stop beeping when the anomaly occurs.

At any rate, without a schematic or a clear understanding of how this circuit works, I'm not sure what to try next.

I hope Authinx plans to redesign these!

[Brian H]

That looks like it is a later design from X10WTI time period. When the older through hole components where getting hard to find.
The Sonix SN8P2501BSB is also in the new X10WTI time period Appliance and Lamp Modules.
If you check the power supply in your UM506. It will probably be closer to 5 volts DC and not the typical old model X10 products 15-18 volts DC.
As the Sonix controller has a VDD of 2.5 to 5.5 volt DC rating.

My test Lamp Module was 5.26 volts DC with NO regulation. Turn On module and the voltage went down from the small extra gate current to the Triac.

My test Appliance module had a 4.2 volt DC supply and a zener diode for regulation.

If you find the later UM506 also has the lower logic supply and maybe no regulation. I could see it being more susceptible to noise.

[toasterking]

If you find the later UM506 also has the lower logic supply and maybe no regulation. I could see it being more susceptible to noise.

I don't think that is the case here.  The hot AC pin (or neutral; the blades are not polarized) is connected to the anode of a BZX85C16 zener diode.  I measured the input voltage to the SN8P2501BSB on the Vss and Vdd pins as 5.028V RMS.  The lowest voltage I ever saw while the relay was being actuated is 5.021V RMS.  I know that it only pulses the relay coil for a half-cycle and I am using a standard multimeter, so I could still be missing it.  The digital display updates every 0.4 seconds but it also has an analog bargraph display which updates much faster, but it wasn't twitching.

Unfortunately, I have several UM506/PUM01 modules with this design and they all have this problem.  I have found the older UM506 modules with an almond-colored case to be much more reliable.  Some date codes of the latter in my collection are 4B6, 5E18, and 6A01.  I also prefer that older design because Ido Bar-tana's momentary delay hack (http://web.archive.org/web/20101029042938/http://www.idobartana.com/hakb/modifying_universal_module.htm) works on it because the delay is determined by charge time of a capacitor.  The newer design does not appear to use a capacitor for timing so I assume it is using the AC zero-crossing frequency.

[toasterking]

I have found the older UM506 modules with an almond-colored case to be much more reliable.  Some date codes of the latter in my collection are 4B6, 5E18, and 6A01.  I also prefer that older design because Ido Bar-tana's momentary delay hack...

And in case anyone is curious about the Leviton 6337, I've one with the same almond color and date code 5C13 with exactly the same internals.