Notes On The Troubleshooting And Repair Of Television Sets


  30.24) Playing NTSC videotape on a PAL TV

"Does anyone know if NTSC VCRs (NTSC is a special feature in Ireland) require
 an NTSC capable television too, or can they convert NTSC signals to PAL
 (seems unlikely)?"

(From: Jeroen H. Stessen (Jeroen.Stessen@ehv.ce.philips.com)).

There are 4 possible answers:

1. The VCR does not convert an NTSC signal to PAL, it outputs pure NTSC and
   you need an NTSC-compatible TV to view it.

2. The VCR converts NTSC 3.58 to NTSC 4.43 and you need a PAL-TV adapted to
   NTSC 4.43 to view it (relatively minor adaptation).

3. The VCR converts NTSC 3.58 to PAL 4.43 but keeps the field rate at 60 Hz.
   That is definitely not a standard signal!  Some standard PAL-TV's will
   permit viewing it, and some Won't!  At least be prepared to see interesting
   artifacts and crosstalks.

4. Conversion to real standard PAL is very expensive, thus unlikely.

The most likely answers are 1 and 3, check the spec of the VCR.  The NTSC 4.43
system has been sold to middle-east and maybe US-military.

  30.25) Buying a TV in Europe

"I have the following question for you specialists:

 Can I buy a TV in any west-european country and use it in any other
 west-european country?  For example, buying a TV in the Netherlands
 and use it in Greece or buying in France and using in England."

(From: Jeroen H. Stessen (Jeroen.Stessen@ehv.ce.philips.com)).

The general answer is: NO.

There are multi-standard TV's that cover more countries, but a TV that covers
them all is extremely rare.  Most countries now have PAL-BG, including all of
Germany.  England has PAL-I, the analog sound is at a different frequency and
the digital sound is their own variety of Nicam.  France has Secam L-L', mostly
incompatible with anything else.  I don't know about Greece, probably PAL-BG.
Most Philips high-end sets can do PAL-BG, Secam-BG and NTSC (the latter from
the baseband video inputs only).

(From: Allan Mounteney (allan@amounten.demon.co.uk)).

The answer is YES.  Well, at least one.

Reason I know is that I was with a company that made computers
with TV-OUT for world wide use and wanted something that could
show that the TV Out worked for various countries.

This ONE and ONLY one we could find Three years ago came from
Germany and covered PAL, SECAM and the American NTSC systems and
came with a note that said from the time of making/selling that
set it would not work in just one small country in South America.
All features (including audio) were adjustable from the front
panel Menu and it was a Grundig 17" job. I am advised that there
is a load of others on the market now.

The company who seemed to know all about these international sets 
and gave us good service at that time was Andrew McCulloch Ltd in
Cambridge UK. Phone #44(0)1223-351825 

  30.26) Could a TV be modified for 3D (stereo) display?

The whole idea of stereo 3-D vision to put the left and right views to the
appropriate eyeball.  There are two common ways of doing this:

1. Use different colors for the two views with color filters in from of
   each eye to separate the views.  This is what were often used for
   the really bad (content wise) sci-fi movies of the '50s.

2. Display alternate views on the same monitor screen but use LCD shutter
   glasses to allow each eye to only see the appropriate view.  This requires
   increasing the refresh rate to avoid unacceptable flicker.

The first approach can be used with any TV and a pair of monochrome
video cameras.  Of course, true color cannot be used since pure colored
images are needed to separate the stereo views.

Alternating views with synchronized LCD glasses is a possibility but
on a standard TV, the resulting refresh rate would be 30 Hz with a 50%
duty cycle which is likely to be useful only as a short experiment - else
your viewers will likely develop splitting headaches.

  30.27) Displaying TV on a computer monitor

My general recommendation is that if you have the space, buy an inexpensive
TV - the quality in the end may in fact be better.  And, it will be usable
without tying up your expensive monitor and (maybe) PC.

While various convertors are advertized to use a computer monitor
with video from a VCR or other source, keep in mind that if it sounds
too good to be true, it probably is like the claim of a $200 box for this:

OK, let me get this straight - this card/box will enable a 31.4 KHz horizontal
scan rate monitor (VGA) be used as a TV - yes or no?  It thus includes a video
A/D, full screen frame buffer, D/A, and all the other tuner stuff for under
$200?  I don't think so.  A scan doubler - which is a subset of the above -
will not result in a high quality picture since it will display pairs of
lines interleaved.  Or does the impressive advertisement leave out the
key requirement that the monitor sync at the NTSC horizontal scan rate
of 15.734 KHz (most newer monitor do not)?  Or is it a board that plugs
into a PC and indeed does use the resources of the PC including the VGA
card and bus?

In any case, get a written money back satisfaction guarantee.

  30.28) Displaying computer video on a TV

Assuming this means NTSC:

1. You need to convert RGB to NTSC - there are single chips for this.  Try
   Sony, Philips, Motorola, and others.  These will combine the R, G, B,
   H sync, and V sync into a single composite video signal using a minimum
   of additional components.

2. You need to match the scan rate to NTSC - 15.734 KHz horizontal.  Even
   basic VGA is twice this - 31.4 KHz.  If your video card can be programmed
   to put out interlaced NTSC rate video then this is easy.  If not, it is
   more difficult.  If you want to use anything higher res than VGA, it is
   a very non-trivial problem requiring the construction of a scan convertor
   which includes a video A/D, full frame store, interpolator/readout timing,
   video D/A.  Unless you are an experienced digital/analog designer, you
   really do not want to tackle any of this.

For the special case of VGA->NTSC, you may be able to get away with just
storing a single scan line since the horizontal frequency is (almost)
exactly twice the NTSC horizontal of 15.734 KHz.  A double buffer where
one buffer is storing while the other is reading out at approximately half
the VGA pixel rate should work. With appropriate timing, even lines become the
even field for NTSC and odd lines become the odd field (I may have this
backwards).  It is still not a trivial undertaking.  Also, keep in mind
that the quality you will get on NTSC will be poorer than the VGA due to
fundamental NTSC bandwidth limitations.  Also, flicker for line graphics will
be significant due to the interlacing at 30 Hz.  Even this is a non-trivial

The requirements for PAL are very similar.  For 625 lines systems, the
800x600 is the format that most closely matches the TV resolution.

You can also buy little boxes to do this.  Quality is general not great
as you are seriously limited by NTSC/PAL and the VCR.  Except for
presentations on existing TV rate equipment, it is probably not worth
the effort.  This is totally useless for any serious computer applications.

For professional presentations, modern video projectors are available that
use high resolution LCD panels and real-time scan conversion.  However,
they are quite expensive (up to $10,000!!!).

  30.29) How can I couple 4 TV screens to make them act like only one?

"I've being thinking about how people do these kind of things?
 Is this analog stuff or do they use some kind of digitized
 signal which is then divided to each TV?"

It is mostly digital.  The original master signal is digitized and
stored in memory.  Control codes specify the readout of a (probably double
buffered) frame store.  9 and 16 screen versions are common.  If you
look closely, you will note that the resolution of pictures that differ
is always lower indicating that the whole affair is driven from a single
tape source with appropriate decoding.  Where the pictures are the same,
they may be at full resolution.  Sub blocks of identical pictures may be
at some intermediate resolution.

  30.30) What is Scan Velocity Modulation?

(From: Jeroen H. Stessen (Jeroen.Stessen@ehv.ce.philips.com)).

Scan velocity modulation occurs around the transients in the luminance
signal. The beam is sped up just before and just after the edge and it is
slowed down during the edge. This makes for a sharper edge. On an alternating
B/W pattern (stripes, checkerboard) you will see that the white parts get
smaller and the black parts get whiter. This geometry error is a side-effect.
Some say that this is the main intended effect of SVM.

SVM is *supposed* to be used to compensate for the spot blowup at high beam
current. Peaking does not help to improve sharpness because the higher peak
beam current also gives a fatter spot. SVM *can* work in that
case. Unfortunately it is often misapplied, too much SVM will give a very
unnatural picture, with obvious horizontal geometry errors.

If applied properly, SVM can improve the picture. Unfortunately there has been
a rat race, led by Japanese, suggesting that more is better.

Some people will simply advise turning the contrast down. At low beam current
the spot size will be acceptably small and SVM is not needed. In most, if not
all, cases they will disable the SVM circuit, usually by pulling the supply
connector to the SVM panel. That panel is often fixed to the neck of the
picture tube, behind the video amplifier panel.

  30.31) What is Kell factor with respect to interlaced displays?

(The following is from Bob Myers (myers@fc.hp.com)).

The Kell factor - which has to do with the fact that we're often undersampling
an image from the standpoint of the Gospel According to St. Nyquist - IS
a factor in the reduction of vertical resolution, but interlacing plays
a part as well.  This comes from at least two factors:

1. The receiver usually cannot precisely interleave the two fields.

2. More importantly, there are steps taken to reduce the interline flicker
   which reduce the effective vertical resolution.  This includes running the
   line width of the display somewhat larger than would otherwise be the case,
   and in interlaced cameras, discharging the entire screen (including the
   lines from the "other" field) after every field scanned.

Interlace is particularly troublesome on moving images, where you will often
perceive momentarily "missing" details.  There was a LOT of discussion
regarding the gory details of interlacing in the recent HDTV debates within
SMPTE and other groups.

  30.32) Homemade V-chip (or at least viewing limiter)

Here is an interesting questions:

>      I would like a control box of some sort that controls the 
>   cable signal that comes into the TV. I want to be able to 
>   control the total time a particular child has in his account to 
>   watch, plus the actual channels that he is allowed to watch 
>   (no Playboy or MTV), PLUS the time of day that he can watch 
>   (not during home work time). Programmable by channel, 
>   cumulative time, hour of the day, and day of the week. I also 
>   need a master pass word for parental programming of the kids 
>   accounts, plus be able to watch what I want to at any time. 
>   The kids could use either an individual account number or an 
>   individual "card" of some kind with a PIN like our ATM cards. 
>   This "box" should be secure so that a 14 year old boy can't 
>   bypass it very easily. At least without doing come major damage 
>   so that I'd know it when he did it. I know that this is a lot 
>   to ask, but I'm very familiar with computer programming and 
>   chipset technology, I do know that such a thing can be done. I 
>   just don't have the electronics knowledge to do it.

The following probably won't help you build such a gizmo but here
are some thoughts:

First, I would not attempt to build any of the RF/cable switching
stuff - there are too many variations.  I would suggest trying to
control the control of what you have.  With a cable box, this would be 
relatively easy - just put the box and an IR transmitter in the same
sealed enclosure.  If you have only a cable ready TV, you could substitute
or intercept the remote detector signal inside the set and disable
the front panel controls.

Then you need:

* An input devices - keypad for example.

* A display - a 1 line LCD.

* A microprocessor.  This doesn't need to be much - just to store the
  'account information' including balance, allowable channel and time
  slot map, passwords.  It would need a real time clock.

* An IR remote code transmitter.  This could probably be directly
  programmed by the micro to control your cable box.

Each account would have a means of adding to the balance,
password authentication, etc.

You would have a superuser account for your own watching as well as
changing any of the individual account settings.

Too bad I don't still teach my intro to computer design courses - this
would make a nice term project.

If you have a junker PC, this would be a simple bit of programming
(but quite wasteful of power even for an 8088 based PC).

  30.33) What is Aquadag?

You may see the term 'Aquadag' referring the the black paint covering the
outside of most of the funnel section of the CRT.

(From: Nicholas Bodley (nbodley@tiac.net)).

Aquadag used to be a trademark of Acheson Colloids [Corp.?], I think
around Niagara Falls or Buffalo, NY. It was one of many "-dag" colloidal
graphites; they also made Oildag, Gredag (grease), and Alcoholdag, as I
recall. Unfortunately, it's probably sold in 55-gallon drums minimum. I
hope you can find smaller quantities. Are there any CRT rebuild shops
around the USA?  See the Thomas Catalog (ThomCat) in a library to find

I am pretty sure there's nothing magic about the graphite. If you can find
some reasonably-priced nickel-flake or copper-flake paint (be sure it's
conductive!), you might have an affordable (?) coating. How about plain
metal foil, maybe even ordinary aluminum foil? You surely don't need
current-carrying capacity; you would need a decent adhesive, though. How
to make sure you have continuity between pieces, I'm not so sure; shoot
for really tight crimps that deform the metal and are gas-tight. (This
might, however, be quite unnecessary.) 

  30.34) Combined computer monitor and TV

"This is a 27" VGA monitor which should also be able to be used as an NTSC
 television monitor.  Can anybody comment on it?"

IMO, I think the entire idea of a combined TV/computer monitor is silly
especially when the likely cost premium is taken into account.  Watching
the boob tube will tie up your entire PC.  The optimal size for TV and
computer use is not the same nor are the requirements in terms of scan
rate, resolution, brightness, and sharpness.  Thus, the design will be
inherently more expensive and include more compromises.

So, I will probably be proved wrong by record sales of these things...

  30.35) Interesting TV Switch Mode Power Supply

The following was found in a Sony TV:

                          Q1 switching/reg
                   (+)            ---
                ----+-------------| |---------------+-----------|
          ----  |   |             ---               |          _|_
    AC ---|  |--|   = C1           |                |    diode /_\ D2
    in ---|  |------|---|    +-----+------+         |           |
          ----     (-)  |    | Reg. Drive |         C           |
           D1           |    +-----+------+         C choke     +---- gnd
                        |          |                C          _|_
                        |          |                | +135 cap ___ C2
                        |          |                |  I--->    |+
                        +----------+----------------+-----------+---- + 135

Although at first this appears to short out the line supply, when
drawn like this it turns out to be a valid switching regulator:

Q1 is driven by a pulse width modulated signal a the horizontal rate.

Q1 turns on putting 150 V across choke.  Current ramps up in choke - more or
   less linear until saturation which should not occur.  This time increases
   with increasing load.

Q1 turns off.  Since current in an inductor cannot change instantly, current
   continues to flow, now through D2, C2, and +135 load.  LCR (R of load,
   diode) time constant - charges capacitor and powers load.

It would appear to fail and run away under the following circumstances:

1. Inductance is too low and choke cannot store enough energy even at high duty
   cycle to supply load.  Too high a duty cycle and core saturates at which
   point transistor blows up.

2. Inductance is too high relative to switching frequency so that choke
   does not have time to discharge (its current) before next current pulse -
   DC current will just keep increasing until core saturates.  This could only
   really happen if the switching frequency were too high for some reason
   unless someone changed core material or something like t.

3. Load is too great due to fault elsewhere.

When attempting to diagnose problems with these types of circuits where the
natural outcome of a fault is for one or more expensive parts to fail
catastrophically, it is wise to either use a Variac to bring up the input
voltage slowly and carefully observe the behavior hopefully before too late
or put a load in series with the line such as a 100W light bulb to limit
the current (though this will change the behavior in various ways).

  30.36) The horizontal output transistor substitution jig trick

(From: penguin@datastar.net).

Okay, here's a good trick you can use for almost all tv work. Mount a TO-3
transistor socket on a heatsink that has about as much surface area as the
skin of both fists balled up, actually the bigger the heatsink the better.
Then mount a horizontal output transistor in the socket.  Use an ECG238 or
equivalent.  Make sure you use a good mica insulator, as there will be over a
thousand volts on the collector.

Solder a 1.5 foot red wire (18 gauge or bigger) to the collector, an equal but
yellow wire to the base and an equal but green wire to the emitter (or use
your own color codes).  You may be able to salvage a ready made heatsink with
socket out of an old receiver or TV. Mine came out of some old Curtis Mathes
TV's.  Solder a damper diode with the cathode to the collector and the anode
to the emitter. Add a 200 ohm 1/4 watt resistor from base to emitter. Add
these parts to the socket not the transistor, so the transistor can easily be
changed if you ever need to.

Now you have a very useful test jig. If you are ever working on a TV that has
a blown HOT (horizontal output transistor) you can pull out the bad part and
connect this jig. Then you can run the set at low voltage.

If you have a set where the HOT is running too hot, this method often will
give you some running time, hopefully enough time to find out what the problem
is. Often the bad parts themselves will self destruct or heat up to where
identifying them is easy. Usually a bad flyback will crack and smoke proving
itself to be bad. Once your satisfied that the problem is cured, you can put
the original HOT in knowing it will be safe.

Usually when I power a TV in this way (using a Variac) I'll bypass the series
pass regulator with a jumper. This is easily done by finding the 180 to 330
ohm 15 to 20 watt regulator bypass resistor and putting a jumper across it.
With the regulator bypassed the power supply will go to 160 volts this is why
it is necessary to use a Variac and only run it at about 60 volts. It is
necessary when using this brute force approach, to make sure that all of the
low voltage supplies coming off the flyback are fused with fusible
resistors. Most models do fuse the LV supplies, but some don't. (One
particular RCA comes to mind.)   Another good trick, if your out in the
field and don't have a varactor handy, is to simply pull the series pass
regulator (e.g. STR30130 etc.) and let all the power just come through the 20
w bypass resistor. If the flyback is okay the B+ to the flyback will come up
to about 60 to 90 volts, and in many cases you can even see a dim picture. 
Anything less than 50-60 volts and the flyback is probably bad. Don't run it
this way for more than a minute or two as the the resistor will be dissipating
close to or more than its rated power under these circumstances. Of coarse you
obviously can't use this method with switching power supplies.

Here's a good trick for the Sony tv's that use the SG-613, even though this
device is a gate controlled SCR you can sub a regular HOT like the ECG238 on
your test jig. I used to blow out these buggers to the tune of about $20
dollars a pop til I figured out how to use the "HOT Heatsink Jig". Now with
the jig connected, the horizontal width may not open up all the way, but you
can run these old Sony's like this for about 5 minutes before the HOT jig
starts to get too hot. Usually if they run this long they're ok and then you
can put the SG-613 in knowing that you aren't going to see a bunch of $$$ go
up in smoke. I had a Sony that would run for weeks then blow the SG-613
finally put this one to rest when I changed out the horizontal output
transformer which was separate from the flyback on this oldie.

Always be cautious of the high voltage on the collector of the HOT JIG.

  30.37) Ken's comments on (TV) SMPS repair

(From Kenneth Aaron (kennetha@geocities.com)).

1. NEVER NEVER NEVER power on a SMPS without load, the newer ones especially
   in TVs (not so much VCRs) self destruct when not loaded.

2. The light bulb test is great to see if your SMPS can handle the load of the
   horizontal circuits - when the set does not turn on - you get the initial
   power on then it goes off - best is to disconnect the collector of the
   horizontal output transistor and plug in a light bulb and see if it goes on.

3. Chinese TVs have poor quality capacitors - the latest models mostly have the
   same SMPS so this applies for all.  There is a small electrolyte cap in the
   supply feedback about 22 to 47uF at 50V.  This dries up real fast and after
   2 years or so the voltage B+ goes up from 110 V to anything up to 300 V!
   (not joking here).  I got a tv where the end of the tube was blown off from
   a supply that reached 296 V instead of 105 V. that's over 75KV into the

4. The newer Philips and copycat Chinese models use the main supply to power
   the horizontal.  The flyback is driven by a transistor which has over 2500 V
   on it's collector.  The flyback is built differently as well.  These
   transistors are called 2DS... - do not use a replacement - I did use one
   with a higher voltage and it fried - this is because the ceramic capacitors
   around it along with it's different characteristics changed the 'on' time
   and it overheated after a few minutes.

5. You can always use a BU208D instead of a BU208A, BU508D instead of BU508A,
   etc, the extra diode will do no harm.

  30.38) IR detector circuit

This IR Detector may be used for testing of IR remote controls, CD player
laserdiodes, and other low level near IR emitters.

Component values are not critical. Purchase photodiode sensitive to near
IR - 750-900 um or salvage from optocoupler or photosensor.  Dead computer
mice, not the furry kind, usually contain IR sensitive photodiodes. For
convenience, use a 9V battery for power.  Even a weak one will work fine.
Construct so that LED does not illuminate the photodiode!

The detected signal may be monitored at the collector of the transistor (Q1)
with an oscilloscope.

 Vcc (+9 V) >-------+---------+
                    |         |
                    |         \
                    /         /  R3
                    \ R1      \  500
                    / 3.3K    /
                    \       __|__
                    |       _\_/_  LED1 Visible LED
                  __|__       |
        IR ---->  _/_\_ PD1   +--------> Scope monitor point
          Sensor    |         |
        Photodiode  |     B |/ C
                    +-------|    Q1 2N3904
                    |       |\ E
                    \         | 
                    / R2      +--------> GND
                    \ 27K     |
                    /         |
                    |         |
       GND >--------+---------+

  30.39) UK Satellite TV information

(From: Martin Pickering).

Here is a list of the FAQs and other documents related to UK satellite TV
available at:

* http://www.netcentral.co.uk/satcure/

by adding the appropriate file name to the URL, above, or following the links.

aegir.htm      The Aegir/Dixi/Lenco/Oritron Jupiter D2Mac decoder FAQ
churchil.htm   The Alfaglade Churchill D2Mac decoder FAQ
d2mac.htm      A general discussion about buying D2Mac decoders
digifaq.htm    Chris Moore explains Digital Satellite Receivers
diseqc.htm     An explanation of DiSeqC
dummies.htm    Satellite TV for the beginner
filmnet.htm    Philips BBD-901 FilmNet D2Mac decoder FAQ
galaxis.htm    Galaxis digital receiver specifications
grd150.htm     Grundig GRD150/200/280/300 receiver FAQ
interf.htm     A discussion about picture interference problems
jack.htm       Lots of humorous stories originally published in magazines
lnb.htm        A discussion about various LNBs and frequencies
money.htm      How to make money from Satellite TV!
mrd920.htm     Pace MRD920 D2Mac receiver FAQ
mss200.htm     Pace MSS200/Apollo receiver FAQ
mss500.htm     Pace MSS500/1000 receiver FAQ
nimbus.htm     Mimtec Nimbus receiver FAQ
prdkits.htm    Upgrade kits for Pace PRD receivers explained
products.htm   Index page for SatCure products
reliable.htm   A discussion about making your receiver more reliable
sat1700.htm    Nokia SAT1700 receiver FAQ
sataccs.htm    SatCure accessories page
satbooks.htm   SatCure books page
satfaqs.htm    Index page for all FAQs
satkits.htm    Satcure repair/upgrade kits page
satwalk.htm    A discussion about the SatWalker and other motorised units
scarts.htm     A discussion about Scart connectors - which is best?
spares.htm     A complete price list of SatCure component spares
sparkly.htm    A discussion about "sparlies" ("fischen") and the cures
sr5500.htm     Echostar SR5500 receiver FAQ
srd400.htm     Amstrad SRD400 receiver FAQ
srd500.htm     Amstrad SRD500 receiver FAQ
srd510.htm     Amstrad SRD510 receiver FAQ
srd600.htm     Amstrad SRD600 receiver FAQ
srx200.htm     Amstrad SRX200 receiver FAQ
ss9kits.htm    Upgrade kits for Pace SS9xxx receivers explained
svs250.htm     BT-SVS250 receiver FAQ
tools.htm      A discussion about repair tools
uniden.htm     Uniden UST- receiver models FAQ
which.htm      Which receiver shall I buy?
advice.htm     What to do if your receiver will not work?
ard200.htm     Cambridge ARD200, BT-SVS200, JVC TU-AD1000 receiver FAQ
ctu900.htm     Philips CTU900 D2Mac decoder FAQ
mss100.htm     Pace Prima/MSS100 receiver FAQ
prd.htm        Pace PRD800/900 receiver FAQ
rd480.htm      Cambridge/Matsui RD480 Extra receiver FAQ
srd6.htm       Ferguson SRD6 receiver FAQ
srd700.htm     Amstrad/Fidelity SRD700, SR950, SR950+ receiver FAQ
ss9.htm        Pace SS9xxx receiver FAQ
svs300.htm     BT-SVS300 receiver FAQ
why.htm        "Why am I in business" - a discussion for when you're down!
yourfaqs.htm   Copies of questions and answers - let's have more!

Chapter 31) International Color Television Standards

  31.1) Brief description of international color TV standards

(The following is from Bob Myers: (myers@fc.hp.com)).

Well, the joke was that SECAM stands for System Essentially Contrary to
the American Method....:-)

The basic, oversimplified description of the three common encoding methods
is as follows:

NTSC: Used in North America, Japan, and a few other areas.  Luminance ("black
and white" information) is sent just as it was before color, and color
information is provided in two "color difference" signals (actually, derived
along with the luminance (Y) signal) via matrix multiplication) which
are carried on a "color subcarrier".  The chroma (color) signals are severely
band-limited compared to the luminance signal, which is one reason you can
never fully recover proper RGB from an NTSC-encoded signal.  The color 
information itself is encoded such that the PHASE of the chroma signals,
relative to the reference signal, is important in recovering the color.
As used in the U.S., the broadcast standard provides a line rate of approx.
15,734.26 Hz, and a field rate of 59.94+ Hz*

PAL: Very similar to NTSC, with the exception that the phase of the color
subcarrier is reversed on alternate lines; this tends to cancel some of
the more common color errors seen in the NTSC system.  (The color signals
of PAL are also simple color-difference signals, rather than using the more
involved RGB -> YIQ matrix of NTSC).  In the most common European PAL 
broadcast systems, a line rate of 15,625 Hz and a field rate of 50.00 Hs
are used*.

SECAM: This system is very different from both NTSC and PAL.  Luminance and
color-difference signals are still used, but the color difference signals
are sent separately, on successive lines.  This requires at least a one-line
memory or delay line be provided in the receiver for proper color decoding.
The broadcast SECAM systems usually use similar line/field rates as for
the PAL broadcast standards noted above*.

* - Note: In all three cases, the terms "NTSC", "PAL", and "SECAM" technically
    refer only to the COLOR-ENCODING systems described above; they do not
    specifically imply a set of timing standards or frequencies.  The one
    possible exception to this is the use of the term "NTSC", since the
    U.S. National Television Standards Committee ALSO came up with various
    timing standards for U.S. television.  But in all cases, the color
    encoding method is not *strongly* tied to a specific line/field timing.
    For example, there is at least one broadcast system (Brazil's) which uses
    NTSC encoding, but at the line/field rates more commonly seen in the
    European systems.

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