In the early 1950's the technical journals of the day said "You had
better get ready for transistorized equipment if you want to keep your
job", then again when color TV was making its debut. Now DTV is going
to replace the old familiar NTSC system. I'm looking for some
technical websites to get familiar with this new technology.
Everything from the tuner to the display. I was in consumer
electronics from 1980 until about 2000 and was proficient in my field,
but I've been away from the technology for 7 years now.
There was a time when you could find some good technical books, but
one source, Howard Sams doesn't have much of anything anymore.

I can tell you a few things, but this is not exhaustive.

The main difference is the horizontal frequency. It's now about
31.5Khz for the 480p mode and about 33.6Khz for the 1080i mode.

What we're working on now mostly has a scan converter, or a line
doubler. Usually this works on the full frame, not just on two or
three lines. I have had troubles in these subsystems but that will
become a thing of the past in about a year. Well maybe not.

What they did was to sell a whole bunch of HDTVs without the ATSC
tuner. They have component inputs, but would need an HD cable box or
component tuner to recieve the HD signal. Now we have the situation on
our hands that if the cable companies continue to charge extra for HD
after February of next year, some people are going to watch a signal
that has been down convereted and then up converted.

Anyway, the technology hasn't changed all that much for CRT based
sets. If you have worked on computer monitors you are familiar with
switching scan modes. However the rest of it is a nightmare. Plasmas,
LCDs and DLPs are rarely repairable due to the lack of availability
of, and high cost of replacement parts. In a plasma there are so many
power supplies it is ridiculous. An LCD direct view is likely to get a
power supply problem. In an LCD projection sometimes the heat destroys
the light engine after a time. In a DLP (all DLPs are projection) the
color wheel gets bent out of shape due to heat.

All of the latter are in additon to the usual changing of the lamp and
possibly ballast, which is basically a power supply. Most of these
power supplies are deemed a replacable unit by the manufacturer, and
individual component parts are largely unavailable, unless you source
them yourself.

So a shop that is not an ASC has to operate pretty much like a
boneyard, scrapping a large percentage of the units for parts.

As for theory of operation, these LCD projectors almost always use
three panels, one for each color. A DLP has an extremely fast refresh
rate, which allows them to use only one element, or panel. They run at
at least three times the frame rate and display the colors
sequentially. And for some of them there are more than three colors.
The refresh rate must be commensurately stepped up.

In any projection unit, the bulb not only has to have the right color
temperature, it also needs a specific spectral output characteristic.
For some reason they just can't use the old movie projector lamps. I
believe it is because the US and other TV systems require the exact
shades of red, green and blue to provide accurate color rendition. If
you do not use those exact colors you must rematrix the signals to the
red, green and blue channels.

I believe that within five years CRT technology will be phased out. At
one time we thought that would be great, no more deflection, flybacks,
complex geometry circuits, all the horse**** that came in with the
flatter, squarer CRTs and RPTVs. But when you actually go to service a
non CRT based set, you find out different in a hurry. And that is even
if you know the theory of operation and have a print !

Even CRT based RPTVs have become unbelievably complex. Entire
directories of DWG or PDF files. But even on a paer print it can take
some considerable time to get to the section you need. But even with
this advantage, manufdacturers have a supposedly valid reason to get
out of CRTs.

I doubt a CRT based set will ever be built that can do 1080p. The
horizontal scan rate would have to be 67.2Khz. That is fast even for a
computer monitor. When you have even a 27" flat widescreen TV the
transistors that can push it might not even yet exist, at least in the
general market. And RPTVs need alot of deflection current. Many of
them are still 70 degree deflection, they just can't make the CRTs
much longer. (lengthwise)

Understand this, in magnetic, reactive scanning, the horizontal
windings of the yoke being a constant impedance, you must double the
pulse voltage to achieve the same deflection angle. They already feed
it with around a 1,000 volt pulse. Generate double that. At those
ridiculous frequencies to boot ! There is a limit to just how low yoke
impedance can go. So then you have to step it up with a transformer,
and stepup transformers are avoided like the plague. The flyback is
the main exception.

Hope you found this informative.

JURB

wrote in message
...

I doubt a CRT-based set will ever be built that can do 1080p.

I have a Toshiba IDTV that runs at 63kHz. QED.