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CRT TV MORE RED COLOUR WITH Horizantal lines

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SHIVAKUMAR K

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Dear Experts,

I have a samsung crt flat tv 21" the sound is ok But, videos is not coming. only red colour and horizontal lines is coming. I adjusted the screen in fly-back knob also, but no changes. Electronics_004small.jpg please help me. I have attached the image of TV, please find and PLEASE HELP ME.
 

You probably have a fault in the red video amplifier that causes too much current to flow through the red gun in the CRT.

You need to tell us the model number so we can try to find a schematic with part numbers on it. The fault is likely to be on the small PCB mounted at the end of the CRT where its pins are. There will almost certainly be three identical circuits, one for green, one for blue and the faulty red one.

Brian.
 

Thanks Brian Sir,

The Model Number is, SAMSUNG CS21B501HL 21" flat TV. In crt Neck board, There are only 4-5 transistors and some resistors I found, but there is no any other video amplifier, and I checked the voltage in HOT Transistor middle leg I got 450v DC, If I touch that middle leg the TV display is go to OFF (not tv turn off, only display is go off)......
 

I have been trying to find a schematic for that model. I think I have one but first, please confirm the PCB on the CRT base has three ICs on it. They are probably numbered IC501, IC502 and IC503 and will each have 9 pins in a row.

Brian.
 

Thanks Brian Sir,

I found three transistors that is 2482 and there is no any 9 pins ics.....
 

Are those transistors labeled Red Green and Blue? If so measure the DC voltages on each of them for comparison. Actually if the cathode pins on the tube socket are labeled R G and B those will suffice too.

Larry G
 

Looks like I found the wrong schematic! I can't find the right one though.

The transistors are 2SC2482 which are high voltage types so they will be feeding the cathodes of the three CRT guns. The collector pin will be the one connected to the CRT, probably through a small resistor or inductor. Please measure the voltage on all three collector pins, it is the center pin on the transistor. Be careful, the voltage is probably around 100V but some of the other pins on the CRT can carry as much as 5KV so you will damage a normal testmeter (and maybe yourself!) if you try to measure them.

Brian.
 

The theory I follow (especially if no schematic) is if the voltage on the collector of the red transistor is quite a bit lower than the blue or green, we most likely have a red video circuit problem. If the voltage on the red is quite a bit higher than blue or green, problem is likely a shorted CRT tube.

Larry G
 

Thanks Brian & Larry Sir,

I changed the three transistors and resistors, the problem solved. (I am extremely Sorry for delaying reply) Thanks a lot........


Siva

- - - Updated - - -

How to rectify the problem, if shorted CRT TUBE ?
 

If the tube has shorted - which is extremely rare because it means the supports inside the neck are physically damaged, there is a trick that sometimes works, if it doesn't it means the tube has to be replaced. The trick is to turn to TV upside down and hit it hard! The loose support MAY then fall away and clear the short but there is no guarantee it will work or that it wont collapse again! You turn the TV the right way up again afterards of course! :)

Brian.
 

A short in the tube can be as simple as particles of oxide have flaked off the cathode and are bridging the cathode to the grid. Putting the tube face down then powering on and tapping the neck can jar the particle loose and get accelerated into the bell of the tube sometimes making an arc sound in the process. Sometimes the particles were so large they would pepper the face of the tube with little pinhole dark spots like a mini shotgun blast !! A crt tester that had a function to remove a G1 grid short would put a high potential on the grid to try and fry the particles.

PS - unfortunately crt arcs can also cause an output transistor to fail

Larry G
 

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