SONY - KV-HA21 SERIES TVS. Pin-Cushion distortion - troubleshooting - [WEGA COLOUR TELEVISIONS]

‘X’ shaped picture.  The picture will look like and ‘X’ shape, all the corners will be correct, but right and left vertical boarders will seem to be shrinked inwards at the middle portion.

The fault is technically called “Pincushion distortion” 

The fault is related with its pincushion distortion correction circuit.  It is composed of two Integrated circuits {Ics} (IC851 – MC4558CD) & (NJM2903M), along with three other transistors as pincushion outputs [Q850-Q851 & Q802]. 

    The components in this section will heat up while the TV works. Among the three transistors mentioned above, Q802 is a MOSFET.  It is the Pincushion Output transistor.  This transistor will be screwed on to a metal heat sink to radiate heat from it while it works. If overheats, this transistor will get opened, making no pincushion output, and the cause for the fault. 

     Just check all the solder terminals of components in this section for any loose solder points.  A loose solder points may be very minute that we can’t see it without using a magnifying glass. So it is advised to resolder all the suspected solder terminals of components in this section, by applying a little more solder, without making any solder bridge short in between adjacent solder terminals.  This is the first thing to do before replacing any component from this section. Check Q851 {PNP} transistor for short.  In most cases, this will be the fault.  Check R868-10 Ohms, R869-1Ohms, Zener diode D805.  Replace these components, especially the Zener diode, even if it tests well with multimeter test.

Replace the electrolytic capacitor, C865-100MFD 16V.  Check R888-220K, R887-220K and R889-100k for open.

IC failure to this section is very rare.  Even though if R889 mentioned above has open, and R887&888 are not, IC 851-MC4558CD will get damaged.

LED BLINKING CODES - or Error Codes - SONY WEGA TRINITRON - HA - SERIES Color TVs

No picture, No sound. Standby LED blinks six times or stays lit without any blink.

Suspected parts

[1] LOT [Line Output Transformer] [NX 4751 M34A]

[2] Horizontal out transistor [2SD 2624-CA]

[3] ABL [Automatic Brightness Limiter] resistors (R511, R512, R568).

      All part numbers will be printed on both sides of the printed circuit board.  Check ABL control resistors (R511,R512,R568, R513 & R510) for open.  If any one among them did fail, the main system control IC will sense it as an over voltage, and will give you indication as six blinks of standby LED.  Don’t misunderstood it to be an over voltage indication. Check components attached to pin number ‘2’ of LOT, before replacing it.

LOT fault detection

If 135VDC drops as set is switched ON

     Desolder out the horizontal output transistor [Q801 – 2SD2624-CA], and switch ON the set without it. Now check whether the voltage drops or not.  If not, replace the transistor with a new one, and switch ON the set for a short period of time, say 3 to 5 seconds.  Switch it OFF, unplug the set from AC mains, and feel the heat of the replaced transistor.  If it overheats within this short period of time, make sure that LOT is defective.

     If the voltage drops without connecting the horizontal output transistor, check [C807-330PF, C808-0082PF, C814-12KPF & C812-0.033Uf (yoke return capacitor), for any leak or other defects.  Check C811-1Uf 250V too.  Replace it with a new one.  If any of the low value capacitors indicated above gets opened, horizontal output transistor will get shorted as soon as we switch ON the set.  This is a common fault and should be checked well, if horizontal output transistor found shorted [Collector to Emitter leak]

   Before replacing the horizontal output transistor with a new one, check these capacitors, and replace them if suspected.  It is a best practice to replace these capacitors, along-with horizontal output transistors.  Check all the solder terminals at horizontal output stage circuit, for any loose or dry soldering.  Re-solder all the suspected solder terminals, by applying a little more solder, without making any solder bridge short between adjacent solder terminals.

SONY WEGA SERIES – KV-HA21M80/H - KV-HA21M81 - Trinitron Color TVs

Sony WEGA Color TVs - KV-HA21M50 - KV-HA21M80 - KV-HA21M80/H - KV-HA21M81 - KV-HA21P52 - KV-HA14M80 & KV-HW21M83

Symptoms 

 Black screen with no sound or bright horizontal line across the screen, standby LED blinks four times, or  stay lit.

Total vertical sweep failure is the fault.

     Vertical oscillator or output section has the fault.  Check all the solder points at (IC551 – AN5522), for any loose solder.  Advised to resolder all the solder points of this IC (7 of them) by applying a little more solder to each solder terminals, without making any solder bridge short in between adjacent solder terminals.  In most cases, the fault will be of loose solder points to the terminals of this IC.  Check (R533 – 2.2 Ohms] for open. If resoldering these points does not help you check the input +ve voltage at pin number 2 of this IC. It should be around 13VDC (+13V vcc).  Check the voltage at pin number 4 of this IC.  It should be around – 13VDC (- 13V vss). 

     If (+13VDC) at pin number ‘2’ is absent, check [C501, C504, D503 & R508].  Voltage to this IC is derived from LOT pin number ‘9’.  Check all the soldering terminals at LOT for any loose.  If found, resolder them by applying a little more solder.  If (- 13DC at pin number ‘4’ is absent, check [C502, C503, Zener diode D502 and R507].  All these component numbers will be printed on either side of the printed circuit board, and are easy to detect.  If all these components are OK, and still there is no vertical output, check whether IC AN5512 heats up abnormally.  If it does, make sure that IC is faulty, and should be replaced. 

     In most cases this IC fount to be faulty, causing vertical sweep failure. When you replace this IC with a new one, zener diode (D502) should be replaced along with.

Just understand that, the voltages to this vertical output IC is generated by LOT, up to that stage is working fine.

     In this model Sony sets, this is a common fault found.

SONY WEGA SERIES TVs – POWER SUPPLY FAULTS

KV-HA21M50_KV-HA21M80_KV-HA21M80/H_KV-HA21M81_KV-HA21P52_KV-HA14M80 & KV-HW21M83 : POWER SUPPLY FAULTS

Cont:-

Section –2

       We have already reached half the way by troubleshooting power supply section.  We have found that here is no fault with mains ON/OFF switch, Rectifier Bridge, switching regulator IC, posistor.  The main component to check further is (R610 – 33Kohms 3W) resistor, which supplies voltage to the internal circuits of the switching IC.  This is one among the important test point.  Check the voltage at (Pin-4) of regulator IC.  If there is no voltage, check this resistor for open.  If it is found OK, check the zener diode (D603) for short.  Replace it, it is best.  If switching regulator IC found shorted, you have to check all the components on the primary side of the SMPS power supply.  Even a small ceramic capacitor can cause severe trouble to switching power section.

      It is recommended to use a 100W filament type bulb at the secondary [135] VDC line, after disconnecting (R502), the serial resistor connected to LOT power supply.  You can reconnect this after finishing the power supply work. When a set comes to you for repair, with dead power regulator section, with shorted switching IC [STR F6707A], be very careful, and check all other components, for any short, open or any other trouble.  Replace these components, even if they are found good. [C610, D605, R608, R605, D603&C606]. If power regulation is found poor, check and replace (IC602 – SE135N) and optocoupler (PH600).  If STR are is found shorted, you have to replace all the above mentioned components, otherwise the newly replaced STR may get fail, as soon as you switch ON the set. 

Check all the solder terminals of SMPS transformer, and other components for loose soldering.  This is the main fault for most of the Sony set.  Resolder all the suspected solder points by applying a little more solder, without making any solder bridge short in between adjacent solder points.

 

C 623 & C 602 are very important capacitors, even though they are very small.  Replace both of them with same value.

Will come with other faults to this TV soon.

SONY WEGA SERIES TVs – KV-HA21M50 - KV-HA21M80 - KV-HA21M80/H - KV-HA21M81 - KV-HA21P52 - KV-HA14M80 & KV-HW21M83 : POWER SUPPLY FAULTS

The set will be dead, no standby light, no response to power.

Section - 1

The power supply section of the set is dead.

      We have to begin with its ON/OFF switch first. Check the ON/OFF switch for its pole continuity. On rare cases, any one pole of the power switch will be defective.  The switch is a DPST [Double Pole Single Throw] type.  If any one among these poles has an internal contact defect, no power will get into the power regulator of the set and thus dead condition.

     If switch is found OK, come towards fuse [F600 – 3.15 Amps].  All component numbers here se refer can be seen on its printed circuit board, printed on both component and foil side. If fuse is found blown up, take a pause.  Never put any more fuse, as there will be specific reason for this fuse to blow up.  We must find it out first.  If we insert a fuse without rectifying the problem to which the present fuse has been blown up, it may make more damage to components. Fuse is used here as a protection device to any short-circuit that may occur to internal circuits.  Just find the reason for its failure, is the first thing to do. Just follow the circuit.

     A special care should take before power up this chassis.  We must have to detach the degauss coil connection plug out to place the main board in service position.  Here the set uses one posistor [THP 600] with three terminals.  A resistor [470Ohms/3W] is connected with its terminal [1] to AC supply line.  Desolder this resistor out, or just lift up a little to get it disconnected from the circuit.  Otherwise, a tremendous current will follow through this resistor without degauss coil connected, when we switch ON the TV after fuse replacement. It is best to desolder out the degaussing posistor out from it, till all the other work has been done and resolder it after. Moreover, if this posistor has shorted internally, the fuse will blow out as soon as we switch ON the TV.  If fuse does not blow out when this posistor has been removed from the printed circuit board, we can make sure that the short inside this posistor caused the fuse to blow out.  If this is the case, without this posistor, the set should work well.  Then we have to replace this posistor only. The work is over.

     The next step is to check the mains bridge rectifier [D601] and mains filter capacitor [C603]. But before checking these come towards the ‘switching regulator’ IC [D600 – STR F6707A], a most susceptible component in power supply section.  Locate its pins (1&2).  Check the resistance between these two terminals.  It should never show a short (less than 1k).  If found very low resistance, desolder out this component from the circuit board. No check the resistance across +ve and –ve terminals of the mains filter capacitor.  It should be high. Before touching these terminals with probes of millimeter, properly discharge the capacitor; otherwise, multimeter will get damaged. 

Continued on section-2

LCD TVs. COMMON FAULTS AND REPAIRS - Troubleshooting

       LCD TVs are todays most trend, and they are invading the electronic entertainment market, ad seems to go further. Here are some faultfinding guidelines; with you can understand the fault to your TV to an extent, provided you must have knowledge in electronics.  Sometimes, you may even repair your LCD TV too. 

Let us discuss first with its power supply section, which is more venerable to faults.

Symptom:  The LED at the front panel of the TV do not light up, even connecting the power cord and switch the TV ON.  The unit appears to be Dead condition

There is a relay connected to power supply.  It should work [when it works, you can hear a click sound can be heard after the TV is switched ON]. Listen to this click sound.

Check the status of cable connections inside the TV for any loose. Check fuses fitted with power supply regulator board and any other. Check the input voltage at the SMPS [Switched Mode Power Supply] otherwise called as power regulator board. If all these are found OK, and still the set refuses to switch ON the Relay, and no power indicator LED lights up at its front panel, make sure that the main board is faulty.  There is no repair to it by replacing components.  Replacing it is the only repair work.

Come to other possibilities.

• Is power LED at its front panel is on and the lamp [backlight] is OFF.  If NO, check the connections of the power cable and all other cables connected to the power regulator board. If YES, does the power standby DC voltage [5VDC] is present or not.  If NO, change the main power assembly.

• If [5VDC] is present, check the main DV voltages [13VDC].  If it is not there, check the associated capacitors, especially check the ceramic capacitors if any connected to this voltage. If there is no fault with any of the associated components, and still there is no 13VDC, the power regulator board is faulty, and should be replaced.

• If this 13VDC is present and there is no main 120VDC present, check all the associated capacitors.  If they are also found normal. Power supply regulator board is faulty, and should be replaced.

• If there is 120VDC is present and no 3.3VDC check the regulator IC on the main board, either for open or for loose soldering points at its terminals. Suspect the main boar assembly too in this case.

• Check the voltages at CODEC, 3.3VDC, 8VDC & 9VDC.  If these voltages are there or not there, and the set wont switch ON, make sure that the main board is faulty.  In rare cases, a well-experienced service technician may set it right.  In 90% cases, replacement of the main board is the only remedy.

If 1.2VDC core voltage, and VCC33, VCC12, VCC25 are present, appear at FRC board and still set refuses to switch ON, the fault is not with picture circuits. Then you have to check the LCD panel.

DIRECT TV REMOTE CONTROL PROGRAMMING METHOD

HOW TO PROGRAM DIRECT TV REMOTE CONTROL

There are some people who have a direct TV remote control and did not know how to synchronize it with their devices.  Here are general proceedings to follow.

*  Just turn ON your TV set, and point the Direct TV Remote Control to it, and Press
remote controls' TV button.

** Press and 'HOLD' the 'Setup" button on the remote control until the TV standby light goes OFF state.

***Enter "991" with remote control's numerical buttons.  Now the TV light on the remote should blinks twice.
****Just aim the remote control to TV.  Alternate between pressing "TV" and "Power" buttons on your remote handset.  The television set will turn 'OFF'.  Once it had turned "OFF", Press "Setup"button on your remote control to to lock in and save the code.

*****If you have to search for codes to other devices, and wants to program them with this same      remote control, repeat these steps. Make sure to use appropriate key for the other device instead of TV.

SONY – KV20M - KV20S - Trinitron Color TVs - Standby light Blinks Two Times

    KV21MB - KV21ME - KV21SB - KV21SE SERIES Sony TRINTRON TVs NO SWITCH-ON.  STANDBY LIGHT BLINKS TWO TIMES

Two blinks of standby light with this model Sony sets indicates B+ over voltage.  That is, 130VDC from the secondary winding of the SMPS transformer supplied to LOT [Line Output Trnsfomer, or Flyback Transformer] has exceeded the predetermined 130 VDC, by some other fault to power regulator section.

    Before doing anything, just check for any loose soldering points on the power supply regulator section.  Check all the soldering of Hi-Watt resistors, which will heat up during working.  Repeated heating and cooling may make its solder terminals to get loose contacted.  Normally, these loose contacts are very difficult to detect without the help a magnifying glass.  Best to do is, to resolder all suspected solder points by applying a little more solder, without making any solder bridge short in between adjacent solder terminals.  There will be very close solder points, which can be make shorted when we resolder them. Take so much care when you do this, as this is the main power regulator section, and if any short when we resolder, will make damage to regulator devices fitted with.

    Resolder all the 8 solder terminals of [T604] first. Resolder all the 5 solder terminals of [IC601; power converter].  Check the solder terminals of this IC.  The main chance for poor power regulation may lie with the loose solder points to this power converter IC.  It will heat up considerably more than any other component, as it dissipates much power by it while it works.

    It is advised to replace the error amplifier IC too [IC602 –UPC1093J-I-T]. This is the IC that controls the regulated output voltage.  It is a three solder terminal IC, usually look like a transistor. Replace electrolytic capacitor [C646 – I0UF 450V].  Replace the Zener diode [D637 – 6.2V]. In most cases these must solve the problem.

    Check the voltage at [TP600] with respect to negative.  In short, check the voltage across [C634].  This is the main 130VDC rail that feeds the LOT of the set.  This voltage is generated between winding terminals 14 & 15 of T603.

    Be very careful while working with this section; especially when you work with power ON condition to take the voltages at different points.  Use of a hand glove is recommended when you work with power section. Never allow children to be near you while you work with this section, especially when working with any electrical equipment.  Be an adult to be by your side as precautionary measure.

SONY TRINITRON [KV20 - KV21 SERIES] [BA-4D CHASIS]. Fault - Continuous blinks of standby light, No Pause

    

Continuous blinking of standby light with this models Sony sets indicates that there is some short or data missing from serial data from system control IC (001 – M37273MF-252SP). Pin number 38 of this IC is Serial Clock, and 37 are serial data output.  Check the voltages at these two pins. Check the voltage at pin number 37.  It should be around 3.5 to 4.3 VDC.  If you have an oscilloscope or a millimeter which can measure frequency. Check the digital waveform or frequency with it. All other functions of this TV is controlled by these two signals emerges from the above said two pins of the IC.  If it found Ok, surely the memory IC (IC003-M24C04-MN6T) is faulty.  Replace the memory IC with same type and number.  When you replace this IC, insist on same number, otherwise set won’t even refuse to switch ON.  Check the oscillator crystal (X001) soldered to pin number 25 of the main system IC.  Check the frequency at pin number 25.  If it is found abnormal than specified, replace the oscillator crystal. Check the resistors connected to pins 37&38 [R003 & R032] respectively, for continuity.  If all of these are OK, and still fault is there, check all the solder terminals of this main system control IC, for any dry solder, or loose solder.

Normally, a loose solder to IC terminals are very difficult to detect, as it will be very microscopic, as we cannot detect it without the help of a magnifying glass.  The best practice is, to resolder all the soldering of this IC, by applying a little more solder, without making any solder short bridge in between adjacent solder terminals.  You must have a concept of soldering, and steady hand to do this work.  More important is the patience and concentration.

If you want the service manual to this set, contact me by email, if this set allows you to do so.

SONY TRINITRON TV [ONE COLOUR PREDOMINANT SCREEN]

     
Sony Trinitron sets are of CRT [Cathode Ray Tube] types. The common fault seen in these types of TVs are any one color predominant on screen with sound OK. Either red, blue or green color 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 plugged onto the picture 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 color. If no emission from all guns, results in a blank screen, ie black screen without any display at all. The three-color beams together produces proper colored picture what we see on screen. Pins of the picture tube outside to which video signals are given in appropriate proportion to produce a TV picture bring out these three gun’s terminals. Normally, all these three pins are biased with a voltage of about 170 to160VDC+ve. Take one color gun, as an example 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 emission increases and vice versa. If the emission increases, the color 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 respect to the other two. If red color is predominant, the voltage at red cathode will be less than the other two. If blue color is predominating, 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 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. Reordering the most of these points on the base card by applying a little more solder will rectify this problem. Other possibility is shorted video output transistor of that cathode. A direct short [collector to emitter] of these transistors will drop voltage to very low at that respective cathode of the picture tube, and that color will be predominant 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 also be replaced. Whatever the case may be, voltage at the respective cathode that emits color 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 color 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 easily, without fearing the damage to the picture tube. After all are found Ok, replug the base card and switch on the TV. The set will be all right. 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

HOW TO CHECK A PICTURE TUBE

    
It is very easy to check the emission of the cathodes of a color picture tube. Assuming all other circuit functions right, including LOT [Line output Transformer] and video output section. There is proper screen voltage; focus voltage and EHT [Extra High Tension].
      Locate the three cathode points on the base card, usually marked as Gk, Bk and Rk. Keep the brightness, contrast and color control to zero position. Take a wire of suitable length, say 50cms or so tie or clip its one end to TVs chassis [negative]. Take one resistor of value 100K 1W, tie its one end to the wire, thus one end of this resistor is now connected to negative chassis with wire and the other end of it is free now.
      Hold this resistor with some electrically nonconductive material [using hand gloves will be better]; switch on the TV, wait a minute or so to get it warm up. Just make an intermittent touch at each cathode of the picture tube base card soldering.
     For each intermittent touch will give you a color flash at screen of the respective cathode. For example, when you touch on the Rk cathode, will give a red color flash on the screen. Similar effect will give for the other two cathodes.  If any one does not get the respective color flash on the screen, check the CRT base-connecting socket for any fault with its contacts to the picture tube pin first.  Replace the CRT base socket is recommended before confirming the fault.
    Never hold it for long duration of time. Only intermittent touch should be done. This process can be used for checking cathode emission of any type of Cathode Ray Picture tubes

HOW TO CLEAN A REMOTE CONTROL

     Normally, all infrared type remote controls are made up of silicon rubber touch pads. Each touch button in it will have a small carbon button inside it, which comes in contact with the carbon track on the internal circuit board. These carbon tracks are connected to various pins of an IC [Integrated Circuit] on the remote's circuit board. For each button touch, generates signals of different frequency, which in turn activates the infrared LED [Light Emitting Diode], which emits infrared light waves of the same frequency. This infrared light waves are received at the device to which controlled [whether it is a TV, DVD, VCR, DVR etc:]. There is an infrared receiver inside the device, usually called "remote sensor", which receives this signals, convert it to corresponding frequency signals, and processed by the main system control IC inside the device and controls it.
     Generally, the remote handset can be called a neglected device. The customer will give no extra care to it. The batteries in the remote control will get damaged after one to two years. It will finally get leaked and the electrolyte in the battery will get in contact with the battery contacts at the battery compartment. This electrolyte will react with metal contacts at the battery compartment, which in turn supplies the battery voltage to internal circuits of the remote control handset. If these contacts get rusted due to this electrolyte contact, supply line to the remote control will be interrupted and the remote control will be dead, even after replacing it with new batteries. First thing to check with for a dead remote is this battery contacts. If there is rust or dirt accumulated, clean them using anything like a razor blade, very small file [seen with some nail cutters]. If the fault was due to battery contact, this process of cleaning will rectify the problem.
     To clean the inner circuits of the remote control, you have to open the remote control. Most of the remote controls' cases are 'press fitted' with lower and upper case parts. There may be 4 to 6 of such locks. Some remotes will have screws also. Detach the lower and upper case, by using any sharp tool. A guitar pick will be efficient to do this work. Just look for the locks at one side, press the lock position inwards and try to lift up or pull out the case part. Do this work with caution and patience. Never try to get it apart quickly. Get the case open without breaking it.
     Inside the remote control, you can see a printed circuit board, with carbon tracks, and IC two or three other components, and an infrared LED. Check the soldering terminals of the infrared LED [two soldering] for any loose solder. If loose solder is detected, resolder that points by applying a little more solder.
     Cleaning should be done very carefully. Never use strong solvents like petrol. Rectified spirit is most preferable. Medical quality turpentine can also be used. This can be bought from most of the medical shops. Just dip a piece of soft cloth in this solvent, and wipe out the carbon track and inside of the touch pad. If you use petrol for this purpose, the rubber part of the touch pad will get damaged and will turn sticky. After clean up, let it dry under a fan for some time. Reset the unit as it was before. If no other damage to IC or other components is there, the remote control should work properly

HORIZONTAL THIN WHITE LINES ABOUT AN INCH SPACE ALL OVER THE SCREEN _ CRT BASED TVs

     This is a common fault to occur in most of the CRT based televisions, 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 in between, all over the screen area. This fault may occur along with color 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 lines across the entire screen area. These are called vertical retrace lines technically. To make it more understand, we have to go to some picture tube electrode details.

     There are three color cathodes for a color 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 focus of picture, and screen grid is supplied with screen voltage, will be much lower than the focus voltage, which determine the emission of the picture tube. There is a final anode supplied with Extra High Tension voltage, can be located at the top side of the picture tube, to which the EHT [Extra High Tension] voltage from LOT [Line Output Transformer] is connected with the help of rubber cap and clip. Without these three voltages, EHT, Screen and Focus, 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 sections 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, (blue Cathode) Rk(Red Cathode) and Gk(Green Cathode). 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 come from LOT windings, after rectification and filtering. There will be one resistor of low value, say one Ohms or so, will be connected series with this winding, in between rectifier diode and winding. Check the voltage at the cathode of this rectifier diode first. If found low replace the diode and the smoothing capacitor. The smoothing capacitor will be between 33 and 47MFD 350VDC rating. Replace both of them. If there is voltage, 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 raster we see have a specific color predominant, that is green, blue or red, check the reverent video out transistors and replace it. It is best to replace all the three video output transistors at the same time with same batch and number

       Check the soldering terminals of video output transistors’ load resistors (usually have values from 12Koms to 15Kohms.  These resistors will heat up while working.  Repeated heating and cooling may make the solder terminals of these resistors to be loose, as a result, supply to the collector point of respective transistor will go low.  In short, first look for any loose soldering points on the picture tube base card [Video Output Card].  In most cases, fault will be there.

PICTURE OK BUT NO SOUND OUTPUT

     The first thing to do with this type of fault, is to check the speaker of the TV. If the voice-coil of the speaker has got damaged, there will be no sound output from it, even if it gets sound output signals from the audio amplifier section of the circuit board inside the TV.  you can check the speaker very easily.  Just take a good dry-cell, connect its two poles [+ve and --ve], with tow pieces of wire, and touch the the other end of these wire to the two terminals of the speaker connection terminals. If the speaker is good, you can hear a 'dub' sound from it for each intermittent touches. If you can hear this sound, speaker is OK, and the fault lies in between the speaker connection terminals to the amplifier section of your TVs circuit board.  In almost all TVs there will be an earphone socket or a headphone socket connected in between the main power amplifier section of the TV and the speaker.  When we push in an earphone pin or headphone pin into it, the internal flip connection will change over [cut and change] to earphone or headphone, and the connection to speaker is terminated.  In some occasions, even after we pull out the inserted pins from the socket, the internal changeover connections may not engaged properly, and a break in connection may occur, thus the audio signals will not come to loud speaker.  Check the connection of this earphone [headphone] for any fault.
     Just connect a good headphone to this socket and listen whether there is sound output can be received by it.  If you get sound output, and not from the speaker, when you unplug the headphone pin from the socket, and the speaker is found OK, replace the headphone socket with a new one of same type.  the fault will be rectified.
     If you do not get sound from both speaker and headphone, the audio amplifier section of your TV's circuit board should be faulty.  There are two main faults which can occur to this circuit.  The first one is with a faulty audio output device.  In most present TV,s, this section is composed of integrated circuits, in short ICs.  The audio output IC will be screwed onto a metal heat-sink, to radiate heat from it while it works. Some may not have heat-sinks and wil be soldered directly to the printed circuit board.  In most cases, the IC will be screwed on to a heat-sink.  You can detect this audio amplifier section, by following the speaker wire.  The wire to the speaker will emerge from this section.  Before doing anything, first check the solder terminals of this IC.  It is a common fault that, soldering loose may occur to this IC's solder terminals.  As the IC heat up while it works, the terminals of this IC will also heat up.  Repeated heating and cooling can make solder terminal joints to get loosed.  Normally, these loose solder points are very difficult see, as it may be microscopically small. It is best to resolder all the solder terminals of this IC, by applying a little more solder, without making any solder splash short in between adjacent solder terminals.  Just use a 20 or 25 Watts soldering iorn with pointed tip to so this work.  If you are familiar with using de-soldering pump, just resolder all the solder from these terminals, and resolder all of them with fresh solder, and it is the best way too. 
     If this also does not help you, just measure the input voltage of this IC.  If it is not here, check the track that supply voltage to this IC.  Normally, there will be a small value serial resistor connected to this supply rail, which may fuse out, if the IC has some internal short with it. If so, before replacing it, measure the resistance of the positive supply pin of the IC with respect to negative line.  the resistance must not be below 25 Ohms or so.  if it is found approximately equal to zero, or much below 15 Ohms or so, make sure that the output IC is faulty and should be replaced with same type and number.
     Before replacing the IC, just measure the resistance of the positive terminal to negative, once more. If it is found to be very low as said above, some other shorted component is there.  Check the ceramic capacitor, connected if any, with the positive supply rail of the IC.  This is a common fault, as ceramic capacitors will get shorted making a dead short circuit, thus cause the fuse out of the current limiting resistor said above.
      So it is best to sully the set after de-solder out the output IC from circuit, and see whether the limiter resistor will blow out or not.  if blow out, check the reason for this fault.  If this happens, the IC you have de-soldered out from the board may good, and the fault was with other component, like ceramic capacitors, or even shorted electrolytic capacitors.
    To 95% cases, the audio output IC has found faulty, by my service experience.