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Raster with many colour , sound OK ,low brightness

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  • 33 Answers

Do you mean that your screen brightness is low?

Posted on Apr 24, 2015

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  • Televison & ... Master
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Degaussing problem. If you wish to get some details; check the site linked here. Pull up older posts. Surf the site with patience. http://electronicshelponline.blogspot.com/

Posted on Apr 24, 2015

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maatmartin7
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SOURCE: Picture cutting after 5-10 min-raster OK sound OK

The vertical ICs on this particular model have by now bad grounds. You will have to resolder this, and check any and all grounds on ICs mounted on heat sinks! Bad grounds are common and plentiful. Good Luck and thanks for asking!

Posted on Jul 04, 2010

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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

I find the colour contrast is very dark could you send me ideal colour settings for perfect clarity thanks


Hello
Adjust the contrast to 55 to 70%; brightness to 45 to 55% and colour to your viewing taste. Now the brightness will be very low I thinks. Advance the brightness and contrast after setiing the colour to Zero. Adjust for a well defined B/W picture first. The advance the coulour. Take reference of the face colour of a news reader at studio. The picture will be perfect. OK.

Jul 07, 2011 | LG 42LB1D 42 in. HD-Ready LCD TV

1 Answer

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.

Sep 06, 2009 | Televison & Video

1 Answer

Screen goes black,with sound


No picture sound ok
Note 1 a Raster is the name for a screen made of lines of brightness
Note 2, A Blank raster has no snow or picture, its just a lit up screen

Sound ok but no raster.
First increase tube's first anode voltage (knob on the loptx) to see if the screen is just too dark.
if after you have turned up the bottom knob on the loptx, there is still no brightness,check, for crt heaters, and EHT 25kv and focus voltage (2kv) and A1's/Screen/G2 voltage is 300-600v.
and check for field timebase (height), the next thing to check is the sandcastle pulse.
If it's present, colour decoder chip is probably faulty or lacks supply from the LT regulators.

NO LINE DRIVE If it's absent,check the line driver, locate the loptr(big and usually has heat sink).
follow the print from the base back to the driver stage , where you will usually find a tiny transformer with 4/5 pins
resolder it, even if it looks good,then with power on, check for voltage on all its pins, 2 should have LT(12v to 32v) or HT (90v to 150v), if not there follow the print back and look for either a transistor(linedrivetr), or the feed voltage line (maybe regulated),
If the voltage is ok on two of the driver transformer(drvtx) legs, the look from the base of the driver transistor to locate the timebase chip
and check round its pins for a 12v supply line, if there ,replace the timebase generator chip

Method of testing line drive, remove line output transistor, and connect a normal red led, across the B/E (longest leg to base), and when you power up the led should lite up.


Trace the pcb back from the BASE leg to find the line driver stage,
Its usually a very small transformer (4/5 legs) and a transistor connected to it,
The driver transformer legs(pins) will be two with voltage and two without
The two with power will either be about HT level (110v=145v) or about LT level(25v)
If not then trace back and look for a biggish 3w resistor.
linedrv.jpg
If the voltages are correct the look for line pulses from the Timebase oscillator chip to the base (some overvolts protection circuits remove pulses if ht is too high).
If the voltage is low and the feed resistor is getting hot then check the base of the driver transistor if its HI over 0.5V then its being turned on by the timebase oscillator chip (protection ?)
If the voltage is zero check the feed resistor
If all seems normal check that 12v is getting to the timebase oscillator chip (IC) (12v regulator?)
Method of testing line drive, remove line output transistor, and connect a normal red led, across the B/E (longest leg to base), and when you power up the led should lite up.

Hope it may help you;
Regards,
VOTIT

Oct 10, 2008 | Philips 42FD9954 42 in. Plasma HDTV

1 Answer

Sanyo TV Model# DS32224


This is usualy because there is either a high voltage regulation fault, or a main power supply regulation fault.

There are many things that can cause this. When the high voltage goes too far down, the raster will enlarge. High voltage regulation can be caused by faulty components in the feedback sensing, or in the high voltage multiplier, or in the flyback windings itself.

A quick way to sort of know if the high voltage is regulating is to wind the brightness and contrast from one extreme to another and observe the raster size. If the raster is changing size with the brightness on the screen, the regulation is not working well. In some of the low cost sets there will be about a 2 to 5% raster size shift in this case. The high end sets will have a near 0% shift in the raster size. A size change of about 2% is acceptable for most sets. If the CRT is weak, this test will not work well, because a weak CRT will not properly load.

If the main power supply is operating slightly over voltage, the raster size will increase. Usualy, the brightness will be a little on the high side when the supply is too high. Voltage regulation faults can be from warn components in the voltage regulator area, or in the feedback control.

This should be looked after by an experienced TV service tech. This type of fault can be involved.

Jerry G.


Nov 09, 2007 | Sanyo DS32224 TV

1 Answer

Colour problem


I have default settings I normally use for most sets before I begin any kind of alingment. Contrast: 90% Brightness: 45% Color: 45% Tint: 50% If the brightness is to high or the contrast to low the color is off. Check your connections, there probably OK, but, it never hurts. If the settings don't help call a local authorized servicer in your area. Hope this helps.

Jun 23, 2007 | LG 42PX3DCV 42 in. Plasma EDTV

2 Answers

Pic Bleeding


this sympton is characterized by the presence of red, cyan, green, magenta, blue or yellow colour in a supposedly plain white raster. proper colour reproduction cannot be expected if the raster is coloured. this symptom is caused by a poor white balance adjustment of by a trouble in the CRT, colour amplifier, color demodulation or colour output circuits. if the raster has a tint of red or cyan, check the R-Y output circuits and the first grid, second grid and cathode circuits of the red electron gun. but if you dont know anything about this, just bring it to a qualified service technician. good luck!

Jan 21, 2007 | Sony KV-35S45 35" TV

1 Answer

Tv showing blue screen with flyback lines sound ok


Flyback lines? Is the picture all white with no brightness control with faint horizontal faint lines? If this is what you are saying, the screen voltage could be bad, and if thats the case, the picture tube or the flyback itself could be bad. You could also have a bad connection on the crt socket

Dec 27, 2006 | Philips Magnavox 20MT133S 20" TV

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