Question about Televison & Video

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Dear Sir, We are suppliers of heater & cathodes to 14" color Tube manufacturers.Our customer has experienced Retrace lines in tubes.When the heater & cathode of these tubes were opened we found both heater & cathode puncture.Also when we inspected our fresh heaters before assembling it to guns we found coating chipoff(insulation cracks).Is this the reason causing for short between heater & cathode due to which both heater & cathode are punctured or is there any other reasons for heater cathode short & puncture & Retrace lines.

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  • praveen_prab Feb 14, 2009

    Retrace lines - My question was does insulation crack/damage to heater leads to Retrace lines.If yes kindly explain to us how it leads to Retrace lines.
    Also as i mentioned earlier when we opened the heater & cathode we found puncture both in heater & cathode which has led to short & then retrace lines.Kindly let us know why this puncture occurs i.e. reason for puncture of heater & cathode.

  • praveen_prab Feb 14, 2009

    In some guns when we opened we have found only heater puncture at the apex & there is no puncture in cathode,in some there is puncture in both which leads to retrace lines.Kindly let us know if there is any other reasons for this to happen.

    Also in some guns when we opened heater & cathode we have found black patches on heater it is somewhat like heater burnt which has lead to retrace lines.Kindly let us know what is the reasons for this to happen.

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6 Answers

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Hi and welcome to FixYa,

This is more of an engineering design rather than a repair issue. Still, to address your concern:

  • the heater filament expands when heated to the point it touches the cathodes. It then becomes part of the cathode and therefore would start emitting electrons;
  • the chipoff coating/insulation cracks weakens the structural integrity of the components. The exposed metal would be emitting more electrons causing that area to burn off faster compared to the coated areas to the point it would have then burn itself a hole;
  • the retrace lines is caused by the same fault. Although there is no increase in the cathode voltages, the electron flow has increased due to the hole, the increase heat (agitation caused by the heater closer to the cathode.
Based on the above, your problem could be cuased by both:
  • the chipoff coating/insulation cracks; and
  • heater filament expanding easily.
Possible solutions may include:
  • improve filament design (make it so that it doesn't expand so much);
  • take into consideration the expansion of the heater filament (reduce its size or increase distance to cathode);
  • reduce heater voltage.
Good luck and thank you for using FixYa.

Posted on Feb 14, 2009

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Welcome to fixya !

The close proximity of cathode and heater and with a insulation crack is surely a recipie for a short and puncture. Try using components without the insulation cracks and try testing the setup. That should confirm our suspicion.

Thanks !

Posted on Feb 14, 2009

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Yes it is the mixture you are useing is causing it you must wait a day or two before before adding and test all between the process. thank you for useing fixya please rate me

Posted on Feb 14, 2009

  • 3 more comments 
  • albert getty
    albert getty Feb 14, 2009

    reheating after main heat is rexpanding and causing your proulbem

  • albert getty
    albert getty Feb 14, 2009

    you need to make a space between coating and medal

  • albert getty
    albert getty Feb 14, 2009

    think of it like this you have two conductors touching you need to keed them apart

  • albert getty
    albert getty Feb 14, 2009

    the black spots are where it is burning do you fill with gas?

  • albert getty
    albert getty Feb 14, 2009

    my first post is a little messed up sorry you must first temper the inside then a day or two later you can put back in to process thank you for useing fixya PLEASE RATE ME ?

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Yes exactly it is because of the shorting up.also check the quality of stuff used.

Posted on Feb 11, 2009

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IF your coating chips off it is exposing a bare metal which would cause you to short out. By this happening when it shorts it burn holes and then you will have puncture holes. Need to try and find a way for the coating to stick on better.

Posted on Feb 11, 2009

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Hi
there is indeed shorting of circuit caused this problem...........

Posted on Feb 11, 2009

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Audio OK but no Picture


NO PICTURE; SOUND OUTPUT OK; PICTURE TUBE BASED COLOR TELEVISIONS.

 

This is a common fault to most of the picture tube based televisions, irrespective of its brand and model number.  There are several reasons for this fault, and 90% of them are related with its video output card, usually located at the neck of the picture tube. Plugged on to its neck.  This card can be pulled out from the neck of the picture tube to repair.  Pull it strait back, no sideways movement should be done, while pulling it out, as it may cause damage to the connection pins of the picture tube.

 

 If you see a color predominant screen that is, if the screen shows excessive blue, red or green color with nice white lines all across the screen, lying parallel to each other and inch apart or so.

 

Check which color is predominant?  Just assume the blue color predominant screen with nice slanting line across the entire screen, about an inch apart to each other.

 

The first thing to do is to measure the voltage at the blue cathode of the picture tube.  You can do this check, while the set is On.  Set a multimeter to measure DC voltage range 500V or above.  Check the voltage at the blue cathode.  You can see markings on the card Bk, Rk & Gk.  All of these are the three cathode connection points.  Among the, Bk is now out discussion point now.

Understand that, the cathodes of a vacuum tube, is negatively biased, that is, if the voltage of the cathode will go down with respect to its screen voltage, the emission of that cathode will increase, and vice versa.  In our case, now, the voltage at the Bk will be less.  Check the voltage of the other two cathode points for reference.  A slight voltage difference, says about 3 volts or so, is Ok, but should never be too below to this.

 

Here one thing to note is, that the voltages of the other two cathodes are high, and the voltage to the blue cathode only is very low.  This is the reason you see a high intensity blue screen.  It were happened to one among other cathodes, say if the voltage at RK is low, you will see a high intensity red screen, and if voltage at Gk is very low, you will see a high intensity green screen.  Of course all this screen will have lines as said earlier [retrace lines] will be there.

 

Let us come to the reasons for this fault.

 

Take the case of blue predominant screen as stated earlier.  It is sure that the voltage at the blue cathode will be low in this case.  That is, the blue cathode pin of the picture tube does not get proper voltage to cut off.

Check the solder terminal of the picture tube base socket pin of blue cathode first.  It is advised to resolder all the crt base connecting socket, soldered on the CRt base board [video output board], by applying a little more solder, because, these solder terminals will heat up while TV works.  Repeated heating and cooling may make the solder terminals to get loose, and no proper connection.

If the solder terminals are OK, there is blue predominant screen, check this resistor connected to the blue video output transistor for value developed or loose soldered.  Check the voltage across the tow terminals of this resistor.  This is the collector current limiting resistor, and will be of a resistance value between 10 to 15Kohms/2W.  If the value of this resistor had developed high, the voltage at the Bk will be low.

If the resistor is found OK, and still the voltage at the Bk is less, than the other two cathodes, check the video output transistor [blue] for Collector to Emitter short.  Replace it is advised.


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Tip

White Raster with thin lines; Sound Ok.


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It is a common fault to occur in most of the CRT based telvisions, regardless of which brand it is. There will be sound OK, and a bright screen with thin white horizontal lines across; at about an inch space, all over the screen area. This fault may occur along with colur shades also, like blue screen with white retrace line, red screen with white retrace lines, green screen with white retrace lines. Let us take the first case. A white raster with white thin retrace line acorss the screen. These are call vertcial retrace lines technically. To make it mor understand, we have to go to some picture tube electrode details. There are three colour cathodes for a colour picture tube, Red, Blue and Green. Two girds are there called Focus and Screen. Focus grid is supplied with focus voltage which in turn determine the cocus of picture, and screen grid is supplied with screen volrage which determine the emission of the picture tube; in short. There is a final anode to all the picture tubes, which supplied with Extra High Tension voltage, can be located at the top side of the picture tube, to which the EHT voltage from LOT is connected with the help of rubber ****** and clip. Without these three voltages, EHT, Screen and Fcous, no raster will be produced. Therefore in our case, there is a raster, so, horizontal output section including Line Output Transformer [LOT] is functioning well, and as far as sound is there, tuner and video IF section are working well. In fact, all other section except, video output section is working properly.
There are three cathode points on the base card, marked as Bk, Rk and Gk. Check the voltages of these three cathodes. In our case, it will be very low or approximately equal to zero. When cathode voltages goes low, emission of the CRT increases, is the reason. There must be a voltage between 120 and 135VDC at these points. Find out the reason for this voltage drop is the next step. The video drive voltages in most TVs comes from LOT windings, after rectification and filtering. There will be one reisitor of low value, say one Ohms or so, will be connected series with this winding, in between diode and winding. Check the voltage at the cathode of this rectifier diode first. If found low replace the diode and the smoothin capcitor. The smoothing capacitor will be between 33 and 47MFD 250VDC rating. Replace both of them. If there is volatge, say 200VDC or so, check whether this voltage comes to the CRT base board or not, If not, check the conducting wire, serial resistors; if used for open. There is no chance of transistor shortage at this time as the raster we see is white. If raser we see have a specific colour predominent, that is green, blue or red, check the revalent video out transistors and replace it. It is best to replace all the three video output transisors at the same time with same batch and number.

on Apr 18, 2011 | Televison & Video

1 Answer

I have a tube tv. the picture as lines and is blur that goes in and out.


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Is the picture set very bright? Try reducing the brightness control to a level where the retrace lines disappear, and reducing the contrast control below the level where the blooming occurs.

If the television is more than ten years old or has many hours of use, the picture tube may simply be deteriorating normally. By nature, they have a limited life span. Before you decide to throw the set out, if you are technically-inclined, try adjusting the bias and screen drive controls for the television as recommended by the set manufacturer (you didn't specify what make or model the set is), and you may get a few months or years of additional life out of the set.

Jul 05, 2011 | Televison & Video

2 Answers

Tv takes up to four minutes to turn on and when it does it has distorted red lines running verticaly across the screen


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Oct 16, 2010 | Samsung Televison & Video

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IM A TV TECH. I HAVE A SONY LCD KP-60XBR800 I HAVE NO RASTER. POWER OK, MENU OK BUT NO RASTER ON TUNER, TUNER VOLTS OK,CAN YOU HELP ME PLEASE. THANKS my email sergioaguirre0182@hotmail.com


check the high voltage with the screen control turned up high where there is no raster. suspect problem within the video circuit where there is no high voltage or defective picture tube.some time when the screen is black and the screen control advanced,you can see if the tv has video or vertical or horizontal problems on the screen.service the high voltage circuit if there is no raster or high voltage is seen.no raster can be caused by the no heater or filament in the CRT.---- a defective picture tube can cause many problems, such as, poor brightness ,missing colors,intermittent picture,poor focus,a single-colored raster,arching in the gun assembly,retrace lines in the picture,negative picture,chassis shutdown,noheater or filament lit and no raster to name a few.an open filament or heater can cause no picture or no raster symptom.a defective CRT can have an extremely bright screen.loose particles of the cathode element can lodge between the grids and cause an intermittent black and white picture. simply tap the ends of the CRT gun assembly and notice if the picture begins to flash off and on.---- with a leaky picture tube after turn on the raster dims and get extremely bright.a dim picture with no green in the raster can result from a bad green assembly. a heater-to-cathode short can cause a raster to change colour or a result in no raster at all.replace the picture tube if there is severe arching in the neck of CRT. excessive brightness with retrace lines and a vertical collapse to a thin line can be caused by a bad coil on the neck board of the picture tube.rejuvenate the picture tube when there is very bright green screen. check for the resistance change on the resistors of the CRT neck board for an excessively bright picture with retrace lines.excessive dust inside the CRT spark gaps within the picture tube socket can cause the very bright raster and the chassis shutdown.a defective video amp,luminance buffer,or reference transistor can cause a bright picture with retrace lines. -------- for getting any required parts to replace you can get it from www.radioshack.com or from www.partstore.com or from www.shopjimmy.com --------- thanks.please do rate the solution.thank you for using fixya.keep updated.

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1 Answer

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1 Answer

Picture Problem


In that set its usually a bad picture tube. The lines you are seeing are called retrace lines. You can take it to a shop and they may be able to rejuvenate the tube

Mar 13, 2009 | Televison & Video

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