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Old October 25th 07, 07:40 AM posted to sci.electronics.repair
JANA JANA is offline
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First recorded activity by DIYBanter: Aug 2006
Posts: 259
Default Moire effects on new TV

With very sharp beam focus it is possible to have Moiré effect. In a simple
explanation, the scanning lines are very thin, and causing a type of optical
beating effect with the rows and columns of the phosphor dots in the
shadowmask.

With a Trinitron tube, the Moiré effect can occur with the horizontal scan
axis. This is because the mask is vertically striped.

With a standard shadowmask, the Moiré effect can occur both vertically and
horizontally.

Sometimes the service tech would adjust the beam focus to be a little less
sharp to mask this effect. This would give a softer picture.

In the higher end CRT TV sets, they had a Moiré filter. What this did was
use some active filter circuits as part of the video processor design to
filter out the bandpass of video response in the range that can produce the
Moiré effect. This allows for sharp beam focus with this effect reduced.

Many high end computer monitors have in their menu, an adjustable Moiré
setup. This allows the user to filter or not filter it. When filtering
anything, some response is taken away. There are tradeoffs for everything.

Have you considered an LCD or Plasma display? They cannot have Moiré
effect, and there are no convergence or purity errors possible.

--

JANA
_____


"svu geek" wrote in message
ups.com...
What would be causing a Moire effect on a new CRT SDTV? There are
smally wavy lines that appear on the middle sides of the tv. I'm
pretty sure they're moire effects. They only appear in a spot that's
maybe 2-3 inches in diameter.

The tv is a 27" flatscreen that's 480i. The tv is connected to the VCR
via coaxial cables and the VCR is then connected to the digital cable
box via coaxial cables. The cable signal/reception isn't all that
great and I get horizontal wavy lines on some analog channels. I think
the moire effects also appear when watching a dvd through composite
cables.

There are no signs of electrical interference.

Even though the tv is a flatscreen, it seems to cave in a bit on the
sides. Older CRTs caved out on the sides.

Do the moire effects mean the tv is defective? Is it something that
will get worse with time? I suppose I want to know if it should be
returned? It doesn't bother me as I hardly notice. I just don't want
to get stuck with a defective tv.