Question about LG 42PC3DV 42 in. Plasma EDTV

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No picture only coloured lines on my screen or a white pannel and moving blue lines? the sound is ok

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Re: no picture

This problem sounds like a failed control pwb. This is somewhat difficult to replace and the the back must be removed, and the control bd is located underneath the main digital bd. assy. The main bd is the bd with all the inputs.

Posted on Feb 14, 2008

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White Raster with thin lines; Sound Ok.

White raster with retrace lines: No picture, Sound OK
(picture tube based telivisions.)

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 | Flat Panel Televisions



Sony Trinitron sets are of CRT [Caothde Ray Tube] types. The common fault seen in these type of TVs are any one colour predominant on screen wih sound OK. Either red, blue or green colour with some thin horizontal lines at about an inch apart will be seen on the entire screen. This is totally a display card problem, which can be seen pluged onto the picutre tube neck. There are three electron guns for every picture tube, which emits red, blue, and green beams, which in turn illuminates the phosphor on the screen to get that colour. If no emission from all guns, results in a blank screen, ie black screen without any disply at all. The three colour beams together produces proper coloured picture what we see on screen. These three gun's terminals are brought out by pins of the picture tube outside to which video signals are given in appropriate proportion to produce a TV picture. Normally, all these three pins are biased with a voltage of about 170 to160VDC+ve. Take one colour gun, as an example and and let me describe the problem.
Let it be a green gun. These guns are called cathodes of the picture tube. If it gets a voltage with respect to its grid, it will emit electrons according to the voltage applied to it. This is a negative process, that is, as the voltage at this pin drops, its emisson incresses and vice versa. If the emission increase, the colour with respect to that gun also will increase and gets predominant at the screen. So when we see a green predominant screen, there will be less voltage at the green cathode with resepect to the other two. If red colour is predominant, the voltage at red cathode will be less than the other two. If blue colour is predominat, the voltage at the blue cathode will be less than the other two.
We must find out the reason for this fault first. Assume that your Tv has a red predominant screen with some thin lines across it, at about one inch apart of the entire screen, it is clear that the the red cathode voltage is very lower than the other two. the main reason for this fault, normally seen in most of the Sony Trinitron, are loose soldering points either to the picture tube base socket or the resistor connected between the red drive transistor's collector point. Resoldering the most of these points on the base card by applying a little more solder will rectify this probelm. Other possibility is shorted video output transistor of that cathode. A direct short [collector to emitter] of these transistors will drop volatge to very low at that respective cathode of the picture tube, and that colour will be pridominant along with lines. Replacing the transistor will solve the problem. In some cases, the resistor connected to that transistor may have blown out. If so, it should alo be replaced. Whatever the case may be, voltage at the respective cathode that emits colour will be very low with respect to the other two. Find out the reason and rectify it. You can compare the voltages of the other two cathodes with respect to the faulty colur cathode. Cathode pins will be marked on the base card, and can be identified. It is best to pull out the base card from the picture tube neck and place it somewhere a safe place without shorting it with other parts of the TV. You can measure the voltages of these points very easly, without fearing the damge to the picture tube. After all are found Ok, replug the base card and switch on the TV. The set will be alright. In rare cases, chroma IC also can be a reason for this fault. if it is faulty, after a short period after switch on the TV, the IC will overheat and shutdown the entire system.

on Mar 21, 2011 | Flat Panel Televisions

1 Answer

1/turning the unit on the screen or panel is all white

You need to resolder the video IC processor they are one smd device

Apr 15, 2010 | Samsung LE40R73BD 40 in. HD-Ready LCD...

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open ur set there is a red cable or could be another colour from behind ur screen the other end is connected to the fly back it have two things two turn on that ajest it n look at ur screen to get it perfic

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1 Answer

Dvd playing blue picture

if it is hooked up with componant, thats the red blue green cables for video, and red white for audio, then you probabily eather dont have the red pluged all the way in, or you have the red audio, and red video---reversed, make sure to check them on the dvd player, and on the tv, if there correct, try using the composit input, that is the yellow red and white

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1 Answer

Blue Line on

Your problem is simple. The problem is your pannel. You need a new one. If it is under warranty, have it fixed. If not buy a new tv.

Mar 14, 2008 | Flat Panel Televisions

1 Answer

Samsung 42 inch

Take to repair shop this is no easy fix it yourself problem!

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