"random" turnon of wall switch

[Steven Bloom]

There were several recent threads regarding a light that randomly turned
on.

After all of the usual insistance that there had to positively be a
generator someplace with the same code, etc., I quit reading them and
decided to let the dust settle.

Now that the dust is gone, I would like to add to the confusion by
pointing out that the WS467 wall switch (and I suspect it's variations,
as well) does indeeed "randomly" turn on. Specifically, under the
correct conditions, a WS467 can "glitch" on due to a power spike from a
large bank of magnetic ballast fluorescents on the same circuit, large
motor, etc.

And filter caps across the 78566 chip, resistor change in the "button"
line nor MOVs do not help.

The solution is actually quite simple, once it is figured out.

The 78566 chip in the WS467 contains 2 unused pins (pin #8 and pin #9)
who's function is unknown to me. However, manipulation of pin #9 can
cause the WS467 to turn on the light.

After discovering this, I have since tied pin #9 to -v and the "random"
light turnons have stopped.

My personal preference is to install a 10K 1/8-1/4w resistor across the
top of the ic between pin #9 and pin #18. A hard wire will probably be
ok, but not acceptable standard practice when dealing with bidirectional
I/O pins.

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G1105 LAB RAT

Name: Steven Bloom Company: Boeing@Motorola
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