Question about Televison & Video

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What is the problem if only retrace line appears on screen and without picture output? what circuit has a problem if b+ voltage increases up to 150vdc and it kills the horizontal output transistor instantly?

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1. Check the opto coupler in the SMPS circuit. Replace it with
new one. DO NOT SWITCH ON TV WITHOUT OPTO COUPLER.
This is feed back, to the switching transistor to control the oscillator.
2. Horizontal out put transistor going defective.

This is due the failure of diode near the EHT coil primary and
the transistor. The reverse leakage of the high voltage diode can not be
checked by the meter. Hence replace all the black coloured diodes
in the horizontal deflection circuit diodes with identical part no.
Horizontal out put TR will get over heated and will rupture. When you
replace with new transistor switch on TV and switch off immediately.
The heat sink should not get heated or warm up. This is the only way
you can protect the transistor when you replace other components one
by one.

After checking all the small components, finally EHT coil.



p

Posted on Aug 19, 2010

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Black screen, sound ok.flyback lines when G2 turned up


Never tune G2 voltage too up to a state, to appear retrace lines on screen. it is bad. It might make the CRT damaged. Check the video output card, and the voltages comes to it. This card can be located at the neck of the picture tube itself, will directly plugged to its back of the neck. Reduce the G2 voltage, in such a way that, there is no retrace lines appear. Be careful. To get some details, http://electronicshelponline.blogspot.com/ Pull up older posts

Dec 12, 2013 | Televison & Video

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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 | Televison & Video

1 Answer

In LG 21" CTV, there is no raster on screen and sound is normal. When increasing screen of FBT only plain raster with retrace lines are appeared. when measuring voltage at cathode of CRT, picture apears...


Hi
Please try testing each voltage of RGB output in the small pcb attached to the CRT. If one of these voltages is missing (they are tipically almost of the same value), replace its output transistor. If all voltages are present, but very high (above 180V), please check the filter capacitor in the RGB supply voltage line near the flyback transformer (47uF/150/200V) by replacing it. It is cheap.
Please be careful when dealing with high voltage section of a tv set as capacitors may store a letal voltage. So disconnect the set from main and discharge any capacitor before dessoldering it.


If this helps you, I shall be glad.

Sully

Sep 26, 2013 | LG Televison & Video

1 Answer

Retrace line with picture in sony hw21, m83


There are two possibilities fof thie fault. The fist one is with increased screen voltage. The second one is with fault related to its vidio output stage circuits. Video output stage circuits are at the picture tube base card. You can see this card plugged to the back of the picture tube. To describe more by this window is impossible, as there are illustrations must be included here. Just visit this site "Electro-help". It is an electronic equipiments servic ehelp site, has all the details about this fault.

Jun 18, 2012 | Sony FD Trinitron WEGA KD-27FS170 TV

1 Answer

Daewoo dtq-206sc have retrace lines


if retrace lines at top of picture the issue is in the vertical circuit--usually a bad filter cap and or the output chip (most of the caps that cause that are 220 uf or 330 uf and connected directly to one pin on the chip.

If retrace lines are across entire screen---likely the master screen control on the Flyback is set too high--causes excessive brightness and the retrace lines.

May 22, 2012 | Daewoo DTQ-20U6SC 20" TV

1 Answer

When ever there is some strong white on the screen it gets distored. For example. There was a white tent on screen and where the light was hitting it it was extremely pixelated and distorted. Ny ideas?


Hello
This fault can occur to mainly three reasons. ABL circuit failure. Low screen voltage or lack of emission from picture tube cathode. Just advance the screen voltage to a little, and observe the result. Screen control can be located on its Line Output Transformer [LOT]. there will be two variable controls built on to LOT marked as screen and focus. Screen control will be at lower side, and focus will bw on the top. Just advance [clockwise movemnt] to a little, not more, advance it till retrace lines are just visible on the screen. Before doing this, set all the picture controls, contrast, colour and brightness of the TV to zero. Once the retrace lines[thin horozontal white lines across the entire screen at about 1 inch distance with each other]; are visible, stop there, turn the screen control counterclockwise to just a point when these lines are just goes off. make this adjustment in a dark room so that you can set this point very correct. After this check the perfomance of the picture. If this does not help you, ABL circuit should be checked for any fault.
If emission of the picture tube has got down, even the screen adjustment said above won't help you. The only way is to replace the picture tube with same type and number. OK.

Apr 16, 2011 | Sanyo DS24424 24" TV

1 Answer

Our set was purchased in 2001. In the last month we've seen a narrow band (2") of parallel, "rippling" lines appear horizontally across the screen, just above mid screen. At first they...


Hello
You are saying about vertical retrace lines. Thes lines will be thin and spread all over the screen at about 1 inch aprat or so, little slanted in position. There are mainly two reasons for this fault. One is vertical output Ic and its supply related. Second is related with increase in screen voltage.
You just open your TV,and adjust the screen voltage a little less, by the help of screen voltage adjuster reistor. It can be located on the picture tube base card, diretly soldered to it. If it helps no need to do anything. After adjusting the scren voltage, increse the brightness contol a little and see whether the lines are there or not. If not it is ok. If yes, you have to go to the vertical output section of your tv. Any screen voltage adjustment should be done after decresing the brightness, contrast and colour controls to its minimum. At this condition you will only see the display items only. Screen voltage is so much related to picture clarity. It must be done in a dark circustace.
If it doesn't help, that is even after the lines are there when you increase the brightness, locate the vertical output section of your TV. It will be normally on the main board, and there will be an ic for amplifying vertical sweep signals. If its supply voltage has some trouble, this type of fault may occur. As your Tv is abot ten years of age, it is quite natural, that most of the capacitors has gone value detained. It is best for you to change all the capacitors, at about 14 nos of them at the same time, as it will cost not much. Change all the capacitors around the vertical output ic is best, as you can't measure the exact value of capacitors, without a capacitance measuring meter. Also look for any bad, or loose soldering is ther to the pins of the vertical Ic. Resolder all the points around and with it by applying a little more solder. This will retify your problem. Ok

Nov 09, 2010 | Sony KV-27FS16 27" TV

2 Answers

Have power but no sound or picture


Do you have high voltage? Check by turning up one of the screen controls to see if you have retrace lines.(pinstripe diagonal lines across the screen) If present turn the screen control back down until the lines just disappear. Check diodes 6003, 6012, 6025, and resistor 3669. If you don`t get a retrace line by turning up the one of the screen controls, check for missing voltages or shorted components in the horizontal output and power supply circuits. Note: Philips TV`s can be tricky even for experienced technicians. Good luck

May 22, 2008 | Philips 50P8341 50" Rear Projection...

1 Answer

Sony trinitron tv kv type


The screen voltage adjustment should be on the back of the high voltage multiplier. It should be marked as "Screen", or "G2". Next to it, is the "Focus" adjustment.

Some models of Sony sets have two focus adjustments. This is for H and V focus.

When increasing the screen voltage will usually increase the wear factor of the electron-gun assembly in the CRT. This is because it is increasing the screen bias current.

When increasing the screen bias, the brightness will increase a little. When the CRT is weak, this may produce visible retrace lines more so than on a good working CRT. This is because the excessive screen current will stop allowing the electron-gun assembly to work at its proper cut-off level in order to allow the blanking drive to bias it off during the retrace period.

Increasing the screen bias will usually cause a shift in the colour temperature especially in the low level gray colours. This is because the AKG reference for the electron-gun biases will be offset due to the differences in the electron gun performance characteristics change.


Jerry G.



May 03, 2008 | Sony FD Trinitron WEGA KV-36HS510 36" TV

1 Answer

Very poor picture


  • your problem is called picture with retrace lines.
  •  your problem is in video output circuit
  • as you are saying that it was off for a year that means there is possibility of loose contact in that section.
  • plz check the following
  • supply to video output absent or loose print.
  • loose connector in crt base.
  • crt base loose
  • voltage on screen control or g2 absent or wire loose.
  • screen control located on flyback transformer mistuned.
  • hope this will help
  • good luck.

.

Oct 19, 2007 | Proscan PS32125 32" TV

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