I have a samsung touch-screen monitor too, a T220. I had the same
issues, I suspect the same 'cure' will work.
In my case all antennas entering the shack do so via a long underground
duct. Baluns are used where appropriate at the feed-points. Equipment in
the shack is all well bonded and I have no issues with RF in the shack
(or common-mode trash from the house/shack/office 'escaping' out to the
antennas either)
My first attempt at a fix involved bonding the monitor well to the rest
of the shack. adding ferrite of a suitable material to the DVI cable,
with multiple turns, trying a decent mains filter etc.
The issue in my case is not RF in the shack, my shack is genuinely clean
in this regard, this monitor's touch switch sensor is simply very very
sensitive to RF, it consists of a spiral wound capacitive sensor that
must resonate some place near 17m . This capacitative switch drives a
flip-flop output on the sensor, touch once and output goes high, touch
again and the output goes low .
The next thing I attempted was to improve the screening and decoupling
in the monitor in the area of the touch sensor module. This involved
using EMC copper tape to build a grounded shield on all sides (except
the front of course) around the touch sensor. improving the local
grounding of the sensor module, adding RF decoupling SMT caps to the
lines in to the module, and adding ferrite to the 2 ribbon cables going
to the touch sensor. a slight improvement but Still no good on 20 M and
up when beaming in the general direction of the house and running power.
My 'FIX' was to wire the output of the sensor to make the monitor think
that the monitor is always on. the sensor has 4(or 5?) wires in (from
the monitor settings buttons) and 5(or 6?) wires out. the extra wire
out is held at +3v when the sensor is 'flip flopped' on and near 0v when
'flip flopped' off. A small blob of solder between the +3v pad and the
adjacent power on pad at the did the trick. I did not take pictures but
it's pretty easy to find the right pins with a volt meter
With this mod done the monitor still draws less than 1W when the
screensaver powers down the monitor or the PC is off. the touch on/off
switch is really just there for show as the monitor goes into low power
standby in the absence of a video signal in any case.
I got this monitor cheap. the picture quality is excellent but the time
wasted dealing with it's shoddy EMC design was no fun. it's also a bit
of a pig to get apart without spoiling the finish, I would not want to
have a neighbour with one of these..
73
Brendan EI6IZ
On Fri, 2009-09-11 at 19:13 +0300, Kostas Stamatis wrote:
> One of my friends has a new lcd screen SAMSUNG T260
> This screen has a touch switch to turn it on and off.
> When he uses more than 200w under 17m the screen is turnign on and off.
> It seems that the switch feels the rf.. We tried ferrites (mix 32 and
> others) in power supply cable with no result
> Any trick to try?
> Kostas SV1DPI
>
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