Notes On The Troubleshooting And Repair Of Television Sets


  30.9) Tony's notes on setting convergence on delta gun CRTs

(This section from: ard12@eng.cam.ac.uk (A.R. Duell))

The older delta-gun tubes (3 guns in a triangle, not in a line) can give 
**excellent** pictures, with very good convergence, provided:

1. You've set those 20-or-so presets correctly - a right pain as they 
   interact to some extent.

2. The CRT is set up in the final position - this type of tube is more 
   sensitive to external fields than the PIL type.

Both my delta-gun sets (a B&O 3200 chassis and a Barco CDCT2/51) have 
very clearly set out and labeled convergence panels, and you don't need a 
service manual to do them. The instructions in the Barco manual are 
something like:

"Apply crosshatch, and adjust the controls on the convergence board in 
the numbered order to converge the picture. The diagrams by each control 
show the effect".

Here's a very quick guide to delta gun convergence where the settings are
done using various adjustments on the neck of the CRT (if you don't have a 
service manual but do know what each control does, and where they all are -
otherwise, follow the instructions in the service manual --- sam): 

1. Apply a white crosshatch or dot pattern to the set. Don't try and 
   converge on anything else - you'll go insane. It's useful to be able to 
   switch between those 2 patterns.

2. Before you start, set the height, width, linearity, pincushion, etc. They
   will interact with the convergence. Also check PSU voltages, and the EHT
   voltage if it's adjustable. That's where you do need a service manual, I 

3. Turn off the blue gun using the A1 switch, and use the red and green 
   static radial controls to get a yellow crosshatch in the middle of the 
   screen. These controls may be electrical presets, or may be movable 
   magnets on the radial convergence yoke (the Y-shaped think behind the 
   deflection yoke).

4. Turn on the blue gun and use the 2 blue static controls (radial and 
   lateral) to align the blue and yellow crosshatches at the center of the 
   screen. Some manufacturers recommend turning off the green gun when doing 
   this, and aligning red with blue (using *only* the blue controls, of 
   course), but I prefer to align blue with yellow, as it gives a check on 
   the overall convergence of the tube.

5. Turn off the blue gun again. Now the fun starts - dynamic convergence. 
   The first adjustments align the red and green crosshatches near the edges - 
   I normally do the top and bottom first. There will be 2 controls for 
   this, either a top and a bottom, or a shift and a linearity. The second 
   type is a *pain* to do, as it's not uncommon for it to affect the static 

6. Getting the red and green verticals aligned near the edges is a 
   similar process. 

7. You now have (hopefully) a yellow crosshatch over the entire screen. 

8. Now to align the blue. This is a lot worse, although the principle is 
   the same. Turn on the blue gun again, and check the static (center) 

9. To align the blue lines with the yellow ones, you'll find not only 
   shift controls, but also slope controls. Use the shift controls to align 
   the centers of the lines and the slope controls to get the endpoints 
   right. These interact to some extent. You'll need to fiddle with the 
   controls for a bit to work out what they do, even if you have the manual.

The convergence over the entire screen should now be good....

A word of warning here... The purity is set by ring magnets on almost all 
colour CRTs, but on PIL tubes, there are other ring magnets as well - 
like static convergence. Make sure you know what you are adjusting.

  30.10) Saga and general setup for large CRT TVs

(Responses from: Tony (ard12@eng.cam.ac.uk), panic from V.K.)

> I'm having problem(s) with a brand new 40" Mitsubishi tube (direct
> view) TV.  I'm writing this with hopes of getting some basic information 
> so that the dealer doesn't bamboozle me.

> From first viewing (5 minutes after the delivery man departed). I noticed a
> discoloration patch in the top right hand corner (purple when the
> background is blue/greenish when background is white).

As you probably know, a colour TV produces a red picture, a green picture 
and a blue picture on the screen at the same time. You eyes interpret 
that as a coloured picture. If you look at (a normal, non-projection) TV 
screen through a magnifying lens, you should be able to see red, green 
and blue dots, and no other colours. 

Now, there are 3 basic adjustments to getting a good colour picture : 

1. Purity. This means that the red picture is only red, the green picture 
   only green, etc. This is the one that needs setting up on your set - you 
   have a purity problem

2. Convergence. This means that the 3 pictures line up over the entire 
   screen (or as much of it as possible). If this one is wrong, you'll see 
   coloured fringes around objects in the picture.

3. Grey scale. This sets the overall colour of the picture - it means 
   that white is really white, etc. It varies the relative intensities of 
   the red, green and blue pictures.

> I called the store in a panic and they calmly told me to
> press the "degauss" button to eliminate the problem (which I
> quickly learned was spurious magnetization, caused perhaps by
> storage near a speaker in the warehouse?).  Result? Better
> but not cured.

Yes, spurious magnetization (or more correctly a different magnetic field 
around the tube from the one present when it was set up) will cause 
purity problems. 

> The next day I visited the store, and the manager said (again) that
> this was an easily fixable problem, requiring a few waves of
> a degaussing coil.  To appease me, he sends the salesman home
> with me with small (1 foot diameter) coil in tow.  Salesman (boy,
> actually) waves the coil in front of and around set but can't seem to
> remove the discoloration.

Argh... Here's what should have been done IMHO.

1. The set should have been degaussed (a fancy word for demagnetized).

2. They should have connected a 'pattern generator' to the set. This is a 
   piece of equipment that generates various test signals. They should have 
   selected 'red raster' (which will appear to you as a pure red screen), 
   and set up the purity adjustments on that. You should ask to see the pure 
   red raster (and pure green and pure blue if the generator will allow it), 
   and make sure there are no strange-coloured patches. If you like, you can 
   examine the screen through a magnifying lens to check that there are no 
   dots of other colours appearing - I do that when I'm setting up a new TV 
   or monitor.

3. They should then have displayed a 'cross hatch' on the screen. This is 
   a grid of white vertical and horizontal lines. Convergence errors are 
   shown by the lines splitting into 2 or more colours (normally one of the 
   'primary colours' - red, green, or blue, and its complementary colour 
   (cyan, magenta, and yellow)). Note, however, that it's _very_ difficult 
   or even impossible to get perfect convergence over the entire screen on a 
   modern tube, and that you'll not notice small errors near the corners 
   on a TV screen. Note that some engineers prefer to set up the convergence 
   on some other type of display (dots, for example), but you should at 
   least be able to see a cross hatch pattern (all pattern generators 
   provide that one)

4. They should have then displayed a 'grey scale' test display. This is a 
   pattern of vertical grey bars of different brightnesses, from black to 
   white. They should all have been a neutral grey, without colouration.

Note that convergence and purity interact to some extent, and thus if 
either is adjusted, both must be checked (and rechecked). Grey scale 
adjustments interact with nothing else.

I would want to see the set on a pattern generator (at least the patterns 
I've mentioned above) and identify the problems.

> To demagnetize the TV, he says that a large coil is required, that
> encompasses the whole unit; service rep will 'be in touch'.

I've never heard of that - the correct procedure is to wipe the coil 
around the front, top, sides and bottom _NOT the back_ and then move it 
2-3m from the set before turning it off. It doesn't matter whether the 
set is on or off for this, btw. I've not heard of putting a large coil 
round the entire set.  (See the section: "Degaussing (demagnetizing) a CRT").

> After the sales boy leaves, I could SWEAR that the picture quality
> in general is decreased, with people (especially their extremities like
> lips and ears) appearing pinker than before, and also more general
> interference (fringes/noise) noticeable.

The convergence and purity are set by ring magnets on the neck of the 
tube. It's possible that the degaussing procedure has slightly 
demagnetized these, and if so, the whole set will need to be set up. 
Similarly, if any part of the set was magnetized at the factory, then the 
adjustments may have been set up to compensate, and then after 
demagnetization, they'll need to be reset.

> So my questions are these.  Can the original problem truly be FIXED
> with proper sized coil and application?

I don't think the size of the coil will make any difference. I would want to
see that set on a pattern generator, so I could be _sure_ as to what the 
problems are. If the dealers don't have a pattern generator, then they're 
not fit to be fixing TVs IMHO.

> Could I be imagining that the waving of the small coil degraded the
> picture quality?

It's possible, but fairly unlikely. See above

> Should I demand replacement to a new set?  Can I legally ask for
> this, or is it like a new car...you own it, now you deal with
> the service guys forever.

I don't know US law, but in the UK, if a product is defective, you can
demand a refund of the money paid (not a replacement or a repair, a refund).
IMHO, a TV with incorrect colours is defective...

  30.11) Liquid coupling fluid for projection TVs

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

The liquid serves two purposes:

1. It conducts the heat away from the surface of the tiny picture tube.

2. It couples the light from the glass surface of the picture tube to
   the glass surface of the projection lens. Using air instead of liquid
   would give too much unwanted refraction at the glass-air interfaces

I believe that the composition of the liquid is mostly water + glycol,
quite similar to the anti-freeze liquid in your car's radiator, but
without the colorants added that should warn you against drinking it.

A good replacement kit contains not only a plastic bottle of liquid
but also new rubber sealing rings to keep it in, where it belongs.
It's always recommended to buy the original stuff, if you can find it.

(From: markmtf@earthlink.net).

I just wanted to throw my $.02 in since I was one of the original members of
the design team for the first Magnavox and Sylvania PTVs.

I don't recall the models, but essentially, there are several generations
of liquid cooled/coupled PTV designs. One type consists of a set of CRTs with
a liquid cell as part of that component. The other type consists of a liquid
cell that directly couples the CRT faceplate to the lens. 

The liquid is a solution of DI (deionized) water and propylene glycol,
with a small amount of surfactant to eliminate bubbles sticking to the
glass and plastic surface. Distilled water can be used. The propylene
glycol is USP grade, not commercial grade for clarity reasons. You need to
order this through a lab supply company and specify USP grade. If you use
a cheaper grade, the solution may become cloudy. The mixture of your
solution should be somewhere between 50/50 to 80/20 water/glycol. The are
many kinds of surfactant which can cause cloudiness or foaming. You should
probably leave this step out if you are just adding rather than replacing
liquid. If you want to experiment, you might try some fluid from a
photographer darkroom supply store that is used for eliminating water
marks during the film drying process. Just add a few drops to 1/2 liter.
Then heat it up to check for cloudiness. If it works, then you are in
business. Again, if you are careful with filling the cell so that you
don't mix in air, you probably don't need any surfactant.

I probably can't help you too much on the seals or gaskets. It is very
dependent on the specific model. Both types of liquid cells loose the
liquid over time due to vapor traveling through the silicone seals. The
CRTs with the cooling cell used a special RTV for a seal. The CRT/Lens
cooling cell used silicone gaskets. There is a tradeoff on how tightly the
gaskets can be tightened down due to CRT specifications. Some
manufacturers were also working on a expandable chamber to reduce buildup
of pressure when the liquid expanded due to heat. The higher the pressure,
the faster the liquid would evaporate through the gaskets.

  30.12) Comments on color purity, set orientation, and doming

"The problem with my TV is that bright parts of the picture change color.
 For example, white areas may shift towards yellow or blue depending on the 
 orientation of the set.

 What are the possible causes of doming?  I have noticed that the magnitude of 
 the doming effect varies with TV orientation even after degaussing several
 times at the new orientation.  Does this help identify the cause of the
 doming in my case?"

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

The problem with regular shadow masks is 'doming'. Due to the inherent
principle of shadow masks, 2/3 or more of all beam energy is dissipated
in the mask. Where static bright objects are displayed, it heats up several
hundred degrees. This causes thermal expansion, with local warping of the
mask. The holes in the mask move to a different place and the projections
of the electron beams will land on the wrong colours: purity errors.
The use of invar allows about 3 times more beam current for the same
purity errors.

Both local doming and magnetic fields compete for the remaining landing
reserve. Due to improper degaussing, the doming problem may be more visible.
And applying a tube designed for the wrong hemisphere may very well increase
the doming complaints.  It is possible to deliberately offset the nominal
landing in order to get more doming reserve (the shift due to doming is
always to the outside of the tube).  You would do this using spoiler magnets
put in the right places.

Permanently setting the contrast lower is not a real cure because the customer
might not like such a dark picture. A better picture tube (Invar shadow mask)
*is* a good cure (in most cases) but there is the cost price increase.  (This
is mainly due to the fact that Invar metal is harder to etch.)

Also see the section: "Comments on color purity, set orientation, and doming".

  30.13) About instant-on TVs

Most TVs built since, say, 1980 have only the microcontroller
powered from a small transformer when the set is off.  This permits the
remote control or front panel pushbutton to switch the set on.  This circuitry
should be no more prone to catastrophic failure than what is in a VCR or
digital clock.

Historically, there were 'instant on' TVs which kept a substantial portion
of their circuitry live all the time - especially those using vacuum tubes
in at least part of the circuitry (other than the CRT).  In these, there
was a lot more to fail.  Those tubes would continue to change their
characteristics for many minutes when warming up.  Circuits were also much more
touchy - remember all that constant tweaking!  Thus, it made sense from
the users's perspective to eliminate the warmup period and keep those tubes
toasty all the time.

In modern solid state TVs, the only component to really need a warmup period
is the CRT.  All this means is that you have to wait 20 seconds for
the picture to appear.

  30.14) About gadgets to use house wiring as TV antenna

Note that these $10 devices usually contain a single 5 cent ceramic capacitor
as their 'sophisticated electronic circuitry'.  The rest of the fancy plastic
case is just for show.

(The following is from: Greg Smith (LiveTV@en.com)).

Most people mistakening believe that the larger the antenna the better
the received signal.  The truth of the matter is that each element of
the antenna must be cut to a precise length depending upon the
frequency of the signal you are attempting to receive.  Further more,
each element must also be spaced a precise distance away from the
others.  This creates what is commonly called a "directional array".
(see diagram below) By providing enhanced reception (gain) in the
direction the antenna is pointed, it also provides decreased reception
from the sides and back. (directivity)  This prevents "ghosting" which
is caused by the same signal arriving at the TV at a slightly
different time because the signal bounced off of some structure on
it's way to your set.

If you use the house wiring as the antenna, the length will be random
and the orientation to the received signal will also be random.
Therefore it will pickup the bounced/reflected signals just as well as
the primary signal.  IE: lots of ghosting = very poor picture quality.

Any kind of directional antenna, even a small one, whether inside or
outside, should provide a superior quality picture to that from the
device you are talking about.  Even a cheap "rabbit ear" antenna
mounted on top of the set allows you to orient it in the best

If you only receive the VHF channels (2-10) in your area then buy a
VHF ony antenna.  If you only receive the UHF (19-60+) then buy a UHF
only.  If you get some of each then make sure that it is a combination
antenna. If your set has separate inputs for VHF/UHF make sure you
also get one with the proper splitter.


       direction of signal

  30.15) Can I add an S-Video input to my TV or VCR?

Possibly, but why bother?  You will most likely be limited by the TV or VCR's
circuitry anyhow.

All S-Video means is (1) a special connector and (2) separate luminance (Y) and
chrominance (C) rather than composite video.

In a VCR, you will need to bypass the input circuitry and get to the place
where Y and C are separate.  This may or may not be possible depending on its

In a TV, they may never be separate and you will need to substitute your own
circuitry for the chroma demodulator.

It is probably not worth it as you will likely not gain much in picture quality
but if you really are determined, a schematic will be essential in either case.

If all you want to do is allow for an S-video input, there are single chips
which will combine the Y and C into a normal composite video signal.

Also, see the section: "How do I add A/V inputs or outputs to a TV which does not have them built in?" since there may be safety implications in the case of
adding S-Video to a TV without any A/V jacks.

  30.16) How do I add A/V inputs or outputs to a TV which does not have them built in?

For A/V inputs (video and audio) The place to do this is after the video
and audio IF where baseband signals are normally separate.

For audio, in particular, an alternative is to tap into the audio circuitry
which may be elsewhere.  Even the loudspeaker outputs can be used but then
without additional switching, you cannot disable the internal speakers when
you are using your stereo system.

Depending on the model of TV, doing any of this may be trivial to impossible -
or a serious safety hazard.

* Trivial: many low-end models use the same chassis (read this: circuit board)
  as the high end A/V receivers.  Either there will be some parts missing,
  a cable connection to the missing A/V panel, or a missing auxiliary board
  which would have the A/V interface and jacks.  If this is the case with
  your model, then it should be straightforward and safe to tap into the
  circuits at that point.

  A service manual or Sams' Photofact for the set will probably even identify
  the additional circuitry present in the higher priced models with A/V inputs.

  If, on the other hand, everything is crammed onto a single circuit board
  with no evidence of A/V signals, it may be very difficult as suitable
  tap-in points may simply not be available.

* Hazardous: many TVs have circuitry which is not isolated from the AC line.
  If this is the case with your set, then it may be more trouble than it is
  worth to provide the essential isolation barrier between the TV and your
  external A/V equipment.  The only 'easy' solution is to include an audio
  isolation transformer RATED FOR LINE VOLTAGE ISOLATION in each signal path
  to the outside world.

If what you are really after is replacing a dead tuner/IF with your own tuner
or converter, this may be possible but, again, may not be worth the trouble.
The antenna isolation circuitry is probably external to the TV's tuner so
yours could be substituted in its place.  Of course, any user contact with the
transplanted device would then have to be TOTALLY prevented since a serious
shock hazard would be present for all metal parts and connections including
shield grounds.  In addition, many components would likely blow the instant
power was applied if this were not done perfectly.

Unless you intend to always use the direct A/V inputs and forgo the tuner,
you will need some way of selecting between them - a switch or relay.
This could be manual - you push a button or flip a switch - or automatic.
There are all kinds of ways to doing the detection - mechanical, checking
for a low impedance connection, looking for a signal, using a switch, etc.

You will need a schematic - don't attempt this without one (for safety, if
no other reason).

  30.17) Adding variable volume headphones to a TV

"My Mother-in-Law is hard of hearing.  He is not.  Is there such a thing as a
 variable volume headset that can hooked up while maintaining normal volume on
 the main speakers?"

Greetings. But of course... The cost is $9-ish per set and it includes a 9
foot (yup, 9 foot) cable and a handy, in-line volume control. The setup
requires an audio output somewhere on the TV itself - is there a headphones
jack? If yes, all you need is a "Y" (splitter) and two sets of headphones.
If not, hmmm.... Either you or the local TV repair shop will need to add one.
Depending on the circuitry of the speaker amplifier inside the TV, this may
be as easy as splicing in a headphone jack and drilling a hole for it on the
case, or as hard as somehow matching the impedance of the speaker to that of
the headphones. You *will* need to look at the schematic or measure the
speaker/signal.  See the section: "How do I add A/V inputs or outputs to a TV which does not have them built in?" for the very important safety issues.

First, however, make sure they have a TV with a headphones jack or have one
put in (or get a TV that *does* have one).  The 'Y' adapter can be purchased in
any Radio Shack. Any cheapo one will do - no need for gold plating (they will
try to sell it to you ;-) should be under $5.

  30.18) Building a Frankenstein TV

Here is an interesting questions:

"I got a lot of partially gutted TVs at an auction (All the same brand) and
 I'm trying to build a 'Frankenstein TV'.  

 I have a 13" unit with a working power supply board and tuner board in one
 set.  I have another set with a 25" picture tube in it.  I'd like to
 drive the big tube with the guts from the small TV.  Does anyone know If
 I'll blow up my workbench if I attempt this sort of transplant?"

It won't blow up your workbench but the differences are probably significant
enough that the performance would be unsatisfactory if it worked at all.

In addition, this may blow up the power supply board - kill the horizontal
output transistor and/or low voltage power supply itself - as the required
power levels are higher.  If you have nothing to lose, power your Frankenstein
initially through a series 100 W light bulb and Variac.  Then you will be able
to tell if you are even close with less risk of blowing expensive parts.

Of course, this does assume that all the organs your are merging are actually
good to start with.  Why do you you think they unloaded those TV carcasses?

While the same chassis may be used for 19" and 25" sets, going from 13" to
25" is likely to have many differences.

  30.19) Turning a TV (or monitor) into an oscilloscope?

This question comes up so often and it does sound like a neat project to
give a defunct TV a second life.  Don't expect to end up with a Tek 465
on the cheap when you are done.  However, it could be a fun learning

CAUTION: See the safety recommendations below.

You will be severely limited in the performance of such a scope.  TVs and
monitors are designed to operate at a very narrow range of horizontal scan
rates and the high voltage is usually derived from the horizontal deflection.
So, you would need to retain the original deflection system for this purpose
at least.

1. You will need to disconnect the deflection yoke from the horizontal and
   vertical deflection circuits of the TV or monitor without killing the HV.
   (also, doing all this without killing yourself as well).  Depending on
   the design, this may be as simple as unplugging the yoke connector.  More
   than likely, you will need to substitute a load for the horizontal
   deflection coil. A coil from another sacrificial similar TV or monitor
   would probably suffice.

Warning: at this point you have a really bright spot in the middle of the
screen which will turn to a really black spot if the brightness is not turned
way down really really quickly.

2. For the horizontal, you need a ramped current source.  You are driving
   a non-ideal inductor (the deflection coil) so it has both inductance and
   resistance.  Thus the waveform is a trapezoid - a voltage ramp (for the
   resistive part) superimposed on a voltage step (for the inductive part).
   This should not be too difficult.  Don't expect to be able to achieve
   really fast sweep.  Even running at normal TV rates is non-trivial.

3. Similarly, for the vertical you need to drive with a voltage (your signal)
   controlled current source. However, if you are just screwing around, then
   the linearity etc. for the vertical may not be that important.  In this
   case, one way is to put a current sensing resistor in series with the
   deflection coil and use this in a power op amp type of feedback
   arrangement.  (You could do this for (2) as well.

4. There is a good chance that the original brightness control will work
   as an intensity adjustment.  However, with some TVs and monitors, this
   depends on receiving a valid video signal.  You may need to improvise.
   If you do want to control the intensity from a signal source, you
   should be able to tap into the drive signals going to the little board
   on the neck of the CRT.

5. Don't expect high bandwidth, uniform response, or any of the other
   things you take for granted with a decent scope.  That takes work.
   However, as a fun project, this certainly qualifies.  Interchanging
   the functions of the horizontal and vertical deflection yoke (and
   rotating it 90 degrees) may provide a better match of horizontal
   and vertical bandwidth to your intended applications or experiments.

6. With a color TV or monitor, these experiments could be quite interesting
   and educational but there may be color fringing effects since you are not
   compensating for certain aspects of dynamic convergence at all.

7. SAFETY: Once you disconnect the deflection yoke from the TV or monitor's
   circuits, move the original circuits out of the way and put a barrier
   between between you and the rest of the TV or monitor. All you will need are
   connections to the deflection yoke on the CRT (unless you want to do
   intensity modulation in which case you will need to drive the video
   output(s) to the CRT cathodes.  I would recommend against doing this
   if your unit is one of those with a totally 'live' chassis as there would
   be additional safety hazards and circuit complications).

(From: Chris Crochet (ccrochet@premier.net)).

Hehehe... Actually, I've done this one :)

I've got two old IBM mainframe terminals, painted like charred metal,
hooked up to each channel of the 'B' speaker outputs on my stereo.  It's
strange looking and always an attention getter when I have guests.  Not
to mention, the long-persistence phosphor they use makes interesting
tracers :)

One caveat, at least on these monitors (I don't know what other monitors
this might apply to).  When you turn them off, the circuitry shuts down
in the following order: horizontal drive first, electron gun second, and
vertical drive last.  Therefore, if there is no vertical deflection,
which would be the case if the stereo is quiet, the active electron beam
becomes perfectly stationary during the course of shutdown, thus burning
a hole in the phosphor.  Oops :)  I found it more effective to hook the
stereo into the HORIZONTAL drive, thus avoiding this problem.  Not quite
like your average oscilloscope.

Another interesting effect -- if the electron gun is active during
vertical blanking interval, it seems to deflect so far that it bounces
off the SIDES of the picture tube, and sprays all over the phosphor,
making some interesting images.

  30.20) Displaying a video signal as a picture on an oscilloscope

I am not sure why anyone would really want to do this other than as an
experiment - it would be interesting one.

If a composite video signal is the input, you will need a sync separator.

You will have to construct a vertical deflection voltage ramp generator
which can be locked to your vertical sync signal.

The horizontal timebase of the scope will be fine for the horizontal
deflection and should easily lock to your horizontal sync pulse or
(if the scope has a TV trigger mode) directly to the video signal.

A video amplifier will be needed if your Z axis does not have an internal
amplifier (you need .7 V p-p to be full brightness range.)  Unless you provide
automatic gain control, this will need to include offset (brightness)
and gain (contrast) adjustments.  Even if there is an internal amplifier, it
may  not have the required bandwidth for the video signal.

However, the overall brightness may be disappointing - a scope is not designed
for overall high brightness.  The beam focus will not be as good as that on
a little TV either.

  30.21) Use of surge suppressors and line filters

Should you always use a surge suppressor outlet strip or line circuit?
Sure, it shouldn't hurt.  Just don't depend on these to provide protection
under all circumstances.  Some are better than others and the marketing
blurb is at best of little help in making an informed selection.  Product
literature - unless it is backed up by testing from a reputable lab - is
usually pretty useless and often confusing.

Line filters can also be useful if power in you area is noisy or prone
to spikes or dips.

However, keep in mind that most well designed electronic equipment
already includes both surge suppressors like MOVs as well as L-C
line filters.  More is not necessarily better but may move the point
of failure to a readily accessible outlet strip rather than the innards
of your equipment if damage occurs.

Very effective protection is possible through the use of a UPS (Uninterruptible
Power Supply) which always runs the equipment off its battery from the internal
inverter (not all do).  This provides very effective isolation power line
problems as the battery acts as a huge capacitor.  If something is damaged,
it will likely be the UPS and not your expensive equipment.  Another option
is to use a constant voltage transformer (SOLA) which provides voltage
regulation, line conditioning, and isolation from power spikes and surges.

It is still best to unplug everything if the air raid sirens go off or
you see an elephant wearing thick glasses running through the neighborhood
(or an impending lightning storm).

  30.22) GFCI tripping with TV, monitor, or other high tech equipment

Ground Fault Circuit Interrupters (GFCIs) are very important for
minimizing shock hazards in kitchens, bathrooms, outdoors and other
potentially wet areas.  They are now generally required by the NEC Code
in these locations.  However, what the GFCI detects to protect people - an
imbalance in the currents in the Hot and Neutral wires caused possibly
by someone touching a live conductor - may exist safely by design in
high tech electronic equipment.  The result - false tripping - is
mostly a problem with 3 wire grounded devices with built in line filters
having capacitors between Hot and Ground but may also occur with 2 wire
ungrounded TVs due to the power-on surge into the highly capacitive
or inductive loads of their power supplies.

  30.23) Multisystem TVs

The question often arise: can my NTSC TV modified to display PAL signals
(or vice-versa).  Unlike a VCR where there are substantial differences
between recording of NTSC and PAL, the problem of displaying the picture
is much simpler.

The following assumes 525 line NTSC and 625 line PAL:

The horizontal scan rates are nearly identical (15,734 Hz for NTSC and
15,625 Hz for PAL), so this is not likely to be a problem.  If these
differed significantly, then there would be design issues similar to
those for multisync computer monitors and this would drive up cost.

The vertical scan are slightly more of a problem with 525 line/60 Hz
NTSC and 625 line/50 Hz PAL.  But it is a lot easier to design vertical
deflection to accommodate a modest variation in rates.  TVs could be easily
designed or modified to accept either.

The color encoding techniques differ but inexpensive ICs exist that
can deal with either standard.  In fact, many are programmable to
do either with a jumper and slight modifications to the external

Displaying a monochrome - B/W - picture on the other kind of
set is usually possible if the set has a vertical hold control
or enough vertical range.  Modifying the chroma circuitry is
more complicated but it should be possible to substitute a
second IC and patch it into the existing video chain.

As far as commercial multisystem TVs are concerned, the real reason we
do not see many of these (at least in the U.S.) is lack of demand.  They
are available if you look hard enough and are willing to pay a premium.
They are readily available on the international market.

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Written by Samuel M. Goldwasser. | [mailto]. The most recent version is available on the WWW server http://www.repairfaq.org/ [Copyright] [Disclaimer]