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TV/Monitor/CRT Fault Diagnosis. (Pictures)

Discussion in 'Audio Visual' started by Shepete, Feb 19, 2003.

  1. Shepete

    Shepete Member

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    TV Fault Diagnosis. (Pictures)

    Admin, I have posted this in "overclocking & hardware" also in "Modding & electronics." Please delete if you don't think it is appropriate.

    Monitor diagnosis.

    I make no claims to being an expert. But I have been doing this line of work for over 25 years.
    When I first had the idea to write this it was going to be a simple guide. It Grew!


    Televisions & Computer Monitors share many similarities. As such, the following article contains reference to both. Generally speaking, what applies to one

    applies to the other.
    This is by no means a comprehensive list of faults, But should cover the most common faults.
    I have the intention of adding or removing material as I see fit.

    Dangers:
    There are many "bightee's" inside a TV or monitor case. Delve inside entirely at your own risk.
    The major dangers, apart from electrocution, while switched on are.

    a: Getting zapped from a charged electrolytic capacitor. The main filter capacitor can store a substantial charge for days, if not weeks.It has a charged capacity of about 350 volts. They hurt.The capacitor can be discharged (obviously power off & disconnected) by shorting a 220 ohm 5 watt resistor across it for 5 or 10 seconds.
    b: Getting belted by the charge stored in the picture tube. Stay away from the lead (with the suction cup on it) that goes to the picture tube.The pic tube can store over 27,000 volts.Once again this charge can be stored for days or weeks.
    c: Injury from an "Implosion". The glass on the back of a picture tube is very thin. It is very easy to break the neck off the pic. tube. Usually this results in no more than a quick "Hiss" as the outside air gets into the tube. But I have heard stories of the glass shattering, being sucked into the tube,
    then bouncing out with great velocity.

    [​IMG] [​IMG] [​IMG] [​IMG]

    Here are some fault conditions & possible causes.

    1:- No power.
    Is the power switched on?
    Is the power light on? If not it is possible that it is a fuse, but not very likely. Fuses usually blow for a good reason.
    Do you have high tension? When switched on at the power switch, monitors usually make a "SSST" sound. This is the picture tube energising. Inside the glass, it is recieving approx. 27 Kv. (Kilo Volts) If you hold your arm. (or something else hairy,) in front of the pic. tube when you turn it on, you will feel the
    hairs stand on end, due to an intense static charge inside the tube.
    This can sometimes be followed by the sound of a relay. This is the Degauss cct kicking in.
    If you here & feel this it is reasonably safe to assume that (most) of the power supply is operating.

    2:- Picture comes on for a while, but gradually fades away,sometimes the pic. will fade back on for a while & then fade away again.
    This is an indication of a "dry joint" in the heater cct. For the electrons to be emitted properly, their need to be a "heater" at the back of the tube. That is the orange glow you see around the neck of the tube while it is running. The heater operates off 6.3 volts, usually supplied by the power supply in monitors, & usually from the LOPT (Line OutPut Transformer) in televisions.

    3:- Screen comes up intensely white.Sometimes with fine white diagonal lines through it.
    Probably a fault with the ABL (Automatic Beam Limiter) part of the cct. The electron guns are being overdriven.

    4:- Screen comes up intensely Red, Green, or Blue, with fine lines diagonally through it. Possibly a shorted picture tube, but probably a faulty drive transistor, or accociated drive circuitry.


    [​IMG]

    5:- Screen intermittently drops one colour, or one colour missing.
    a: Faulty cable.Monitor cables frequently fail around the HD15 plug (High Density 15 Pin Plug)
    b: Possibly pic. tube again. But more likely a faulty drive transistor, or accociated drive circuitry.
    Normal colour bars.
    [​IMG]
    Red missing.
    [​IMG]
    Green missing.
    [​IMG]
    Blue missing.
    [​IMG]
    6:- Vertical collapse. Sometimes intermittent. Sometimes only partial collapse.
    A solid white line across the screen.
    Fault with the vertical deflection circuitry. Many causes, Dry joints, elecrolytic capacitors, Vertical output I.C., vertical Oscillator etc.
    [​IMG]
    7:- Horizontal collapse. The same as a vertical collapse but the line goes down the screen instead of across. This is not often seen because usually the device dies as soon as it happens. If you see a solid white vertical line on your monitor or TV, turn it off IMMEDIATELY, & have it repaired. If it is still running, not to much damage has been done.
    If you are very lucky, you may find a dry joint around the LOPT.
    If the set no longer runs, the horizontal stage has probably blown up. This is serious repair stuff. Probably not worth repairing.
    Far too many causes to list.

    8:- Picture geometry faulty at the sides.
    Pin cushion problems. Because a CRT (Cathode Ray Tube) tries to make a rectangular picture from a pin-point, also the characteristics of the tube, Circuitry is required to try & straighten out the sides. Pin-cushion problems will cause "bowing" of the sides,or picture distortion. on the sides.


    9:- De Gauss.
    Picture tubes being electro-magnetic devices are effected greatly by stray magnetic fields. Magnets, speakers or even turning the picture tube on its side, while running are enough to upset the purity of the screen. If you have green, red or blue patcheson the screen. It is because of either a problem with the automatic Degauss cct, or the automatic degauss cct is unable to cope with the degree of induced magnetism in the screen. Usually a sweep with a degaussing wand is enough to rectify the problem.
    [​IMG]

    [​IMG]
    A degaussing wand in action.
    [​IMG]

    This is a superb image of what misconvergence looks like.
    You can see that the RGB beams don't line up, so you get three distint images, in red, green & blue.

    [​IMG]

    The most common reason most electronic devices fail is due to electrolytic capacitors being "cooked". They can only stand so much heat for so long.This is a common occurrance. One of the power supply signal capacitors, mounted up against a radiator.(Oops, I mean heatsink) Do you think they know what built in obsolescents is?
    [​IMG]
    I hope this is of interest.
     
    Last edited: May 23, 2003
  2. Crash Dummy

    Crash Dummy Member

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    Yes it is :) Thank you. That's a very informative and useful guide.
    One little think i might suggest though is to redo the labels in the pictures because being red they're rather hard to see.

    Other conditions i'd like to know about though are why some monitors screatch and what the noise from TV's is. Screatching and the high pitched emited by TV's absolutely shits me. It almost hurts my head going into a shop full of TV's. It's one of the reasons i'd much rather watch TV using a TV tuner card in my PC. Quiet 85hz flicker free image. Ahhh. Beautiful to the eyes and ears.
     
    Last edited: Feb 20, 2003
  3. OP
    OP
    Shepete

    Shepete Member

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    TV's & monitors's are "full" of oscillators. Virtually everything relies on an oscillator. I would guess that you are quite young, your hearing is very good. I think, What you are hearing is the oscillation of the deflection yoke, The deflection yoke is just a transformer. As the coils oscillate, they vibrate. Although they are dipped in varnish to reduce the vibrations (by glueing them together) sometimes they still emit an audible sound. I suspect that you have acutely good hearing, & can hear sounds that most people can't. I have middle age deafness, which is a big problem for me, Customers bring in TV"s with louder than "normal" "sounds". I can't hear them at all.
    Incidentally, women, (In general) have superior hearing to men.
    Men's hearing, deteriorates after about age 18.
    I think the excepted standard is 20 Hz to 20 Khz. If you are young with good hearing. As you age "evertthing":( works less efficiently. I suspect my hearing is about 20 hz to 9 Khz.
    Such is life.
     
  4. hexnet2001

    hexnet2001 Member

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    what would one do to fix the #6 problem? i have an old crt that does this witht he stand, but once the stant is taken off it works fine
     
  5. Daggoth

    Daggoth Member

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    Great post, I've had people and place and all and sundry warn me about 'the dangers of high-power capacitors' in the back of TVs and monitors, but this is the first time I've actually been able to see the culprits (of course I would've been suspicious of a MASSIVE black capacitor, but I wouldn't have taken a second look at the suction-cup dealie).

    Anyway, I've got a problem with my TV, and I was wondering if you could shed a bit of light on it.
    Can you please explain the causes and cures to 'vertical fold-over' in a TV set. You know, when the picture bounces off the top of the tube and folds back down on itself. My set's had this for at least 6 months, of not more.
    Any ideas would help improve my understanding, I strive to learn!
     
    Last edited: Feb 21, 2003
  6. Crash Dummy

    Crash Dummy Member

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    Hehe. Yes Shepete i'm 18 and my hearing is quite good. I can hear up to around 18,000hz.
    The sound i hear emited from the TV is around 15,000hz if i recall correctly. I used a frequency generator to reproduce the same sound.
    One of the things i love about new 100hz TV's is that the refresh is so high that nobody can hear the high pitched scream.
    On the same topic. Some monitors i've seen like some friends that go to LAN's a couple of them have monitor's that emit a strange squeeling noise, sometimes intermittant sometimes at higher refresh rates others when stuck on 60hz.

    *edit*
    Hey i just noticed you have a NEC 68cm TV in the background :) My parents own one of these. I was wondering if you know if they've got any major faults or things that commonly go wrong with them. In the 3 or 4 years we've had ours we haven't had anything die on it but it's made some strange noises apart from the normal squeeling but it just went away *me shurgs*
     
    Last edited: Feb 21, 2003
  7. OP
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    Shepete

    Shepete Member

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    Presumably, if you tap the case the fault comes on & off. If so it is a "dry joint".
     
  8. OP
    OP
    Shepete

    Shepete Member

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    It will probably be an "Electrolytic capacitor" around the vertical output I.C.
     
    Last edited: Feb 21, 2003
  9. SpeedFreak

    SpeedFreak Member

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    /me calls for admin:

    "ADMIN!!!!!!!!! - PLZ STICKY THIS!!!"

    :D
     
  10. OP
    OP
    Shepete

    Shepete Member

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    I am a little reluctant to go down this path. I have found from experience that people don't like to be told they have bought a piece of "shit". Also of course, personal preference comes into it.
    Back to your question, I have no love for NEC in general. But having said that, This is the first one of these I have had in the workshop. I assume that would indicate they are fairly reliable.
    Incidentally, this TV has an intermittent, audio problem. Runs fine for hours, Then starts screeching & squarking through the speakers
     
  11. Frewy

    Frewy Member

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    Excellent work Shepete:) A picture tells a 1000 words

    Now whos going to do VCR's?
     
  12. OP
    OP
    Shepete

    Shepete Member

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    What do you want to know?
     
  13. othy

    othy Member

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    Shepete,

    (You're going to get this a lot now...)

    When running my TV in 60Hz the top 5cm of the screen flickers. Its worse when the screen is mostly blue. I get the same problem from S-Video, Composite and whether I go through my VCR or directly into the TV. Source is both my computer and dreamcast. Its a fairly new TV and is still covered by warranty but they want to have it for a while with the dreamcast and I'm a little reluctant. Have you ever seen a problem like this before?

    --

    othy
     
  14. Frewy

    Frewy Member

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    I meant a sticky with Pic's and info like your TV post ;)
     
    Last edited: Feb 21, 2003
  15. Frewy

    Frewy Member

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    Is the set able to run at 60Hz ? standard Pal is 50Hz
     
  16. Frewy

    Frewy Member

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    BTW I saw that Cocking show (where you are using the magnet)
    in HDTV on a pro Sony monitor @1080i yesterday and the pictures are stunning the reflexion on the bench top was most notable to me.

    But the HD STB (Panasonic and Digitec) seem to be have trouble with the HD and audio:(

    I have been told that 9 in Sydney have a complete HD Studio now but are not going public with that statement until the Bugs are gone.
     
  17. othy

    othy Member

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    Yeah, it supports it. All versions of NTSC & PAL. Component/S-Video/Composite. I realise the PAL standard is 50Hz :rolleyes: otherwise I would have said it does it all the time...

    --

    othy
     
  18. Crash Dummy

    Crash Dummy Member

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    Heheh Don't be mate. I know it's a peice of shit :p As for that problem with the speakers on the one you've got there i can understand there's a problem with them. Ours is always producing some kinda of noise from the speakers even when it's muted. If you press i think the surround mode button the noise goes away for about half a second while it's switching modes. it's quite annoying but hey what can you do. :)
    I've pretty much begged mum to sell it and find something better but unfortually Dad just won't have it. :(
    One of the very biggest gripes i have about this TV though is just how much the image expands and contracts from pulsating flashes of brightness then to darkness, say a scene in a movie with lots of gun fire or if i display a image from my PC's TV output and working in windows there will be a slight black border that will get larger and smaller when i open windows.
    It was a reasonably nice TV when we got it because we were upgrading from a rather dead 53cm tv that was around 25 years old :D
     
  19. hexnet2001

    hexnet2001 Member

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    exacly right, could this be in any perticular part, or on any of the pcb's?
     
  20. CailYoung

    CailYoung Member

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    I heard the CRT squeal on most TVs is 16kHz but I could be wrong... yes it bugs me too :)

    Cail
     

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