Very Computer

I would like to relate an interesting problem that I discovered. I
recently purchased two refurbished IBM 8514 VGA monitors for both my and
my wife's computers that we have at the house. Shortly after setting up
these monitor I noticed that several x-10 modules both wall switch and
plug in type would not reliably respond to command from either the CP-290
controller or from several of the maxi-controllers in the house. I
presumed that the phase-to-phase coupler needed to be replaced. I built
another coupler and installed it but there was no change in the operation
of the offending modules. I tried substituting the plug-in modules with a
known good spare but again no improvement. I thought back to any changes
in appliances or equipment in the house. The refurbished monitors were
the only change that I could think of. I checked to see that the power
switches to the computers were off as well as the monitors. Still no
improvement. I finally decided to totally unplug the computer systems and
as if by magic all of the x-10 modules and controllers including the rf
remotes were working perfectly. Simply plugging the computers back in the
ac outlet let to immediate module problems. I started to isolate the
computer equipment piece by piece and decided that with either of the IBM
8514 monitors plugged in I started getting module problems. Althought the
power switches on these monitors was turned off there must still be some
sort of circuitry active inside the monitors that emit enough noise to
cause interference with the 120Khz x-10 signals. I tried a couple of
power line filter and settled on the Radio Shack Twin Outlet Power
Protector #26-1395A. I found these at the local store on a close out
table. One of these was used for each computer system in front of the
monitor and cpu. The printer also has a filter for good measure. This
particular filter comprises three fused movs with indicator light for
normal mode and common mode spike protection and a balanced pi-type
filter as well as circuit breaker. Normally you think of a power line
filter to keep trash out of a piece of equipment but it can also be used
to keep trash out of the power line. This has been a bit long but I
thought this might help someone else who might be having similar
problems.

Allen.....

--
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|  Allen Kass, Chief Engineer   WRVQ Radio Q94  Richmond, VA.  |
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Quote:>I would like to relate an interesting problem that I discovered.

<SNIP - Long message deleted>

Quote:> ... Normally you think of a power line
>filter to keep trash out of a piece of equipment but it can also be used
>to keep trash out of the power line. This has been a bit long but I
>thought this might help someone else who might be having similar
>problems.

Some electrical / electronic appliances place a small capacitor (e.g. 0.05
microfarads) either across the power line, ar from each side of the power line
to an internal chassis.  If the capacitor is ahead of the On/Off switch, then
it can affect the power line independent of the state of the switch.  It
affects X-10 signals NOT by adding trash to the power line, but by diminishing
the amplitude of the X-10 signal.   0.05 microfarads "looks like" a high
resistance to 60 Hz power, but "looks" close to a short circuit to the X-10
signals (which is why capacitors of about this value are often used for
phase-to-phase coupling).

I am not saying that this is what happened in your case, and the same fix
applies, which is the one that you already discovered.

--  Ian

Hughes Missile Sys. Co.* phone: 520-794-7176
PO Box 11337           *   fax: 520-794-5452
Tucson, AZ 85734-1337  *

Quote:>Althought the
>power switches on these monitors was turned off there must still be some
>sort of circuitry active inside the monitors that emit enough noise to
>cause interference with the 120Khz x-10 signals.

More likely they are low impedence to 120Khz signal, probably a
capacitor across the power line.

Quote:>I tried a couple of
>power line filter and settled on the Radio Shack Twin Outlet Power
>Protector #26-1395A. I found these at the local store on a close out
>table. One of these was used for each computer system in front of the
>monitor and cpu. The printer also has a filter for good measure. This
>particular filter comprises three fused movs with indicator light for
>normal mode and common mode spike protection and a balanced pi-type
>filter as well as circuit breaker.

This works because the inductor in the filter is high impedence to
120Khz thus preventing the monitor from shorting out all the signal.

Glad you found a solution.

Other things to try are winding your own inductor (power cord around
a steel bolt) or opening the offending equipment and removing the
capacitor.
--
Andy Burgess