SAMSUNG LA26R71 LCD COLOUR TELEVISION: TROUBLESHOOTING AND REPAIR

PART-5

     Now we came the most important section of the power supply.  The switching output section. Here an IC is used for all functions [oscillator and output] to drive an SMPS transformer’s primary winding.  The secondary winding of this SMPS transformer generates all three voltages supplied to other printed circuit boards.  They are 13VDC which appear at pin number 1 at CNM 901, 26VDC appear at pins 1,2,3,4 &5 at CNM 802, and 12VDC appear at pin number 9,10 & 11 of CNM 801.  Pin number 15 of CNM 801 will be a constant 5VDC, and it is the standby voltage.  If this standby voltage is all right, you can see the standby light at the front panel of the TV lights up, as soon as the set is switched ON.  Check the 5VDC first if there is no standby light on the front panel of the TV.  If there is standby light on the front panel, no need to check this voltage.  It will be there.  Check the other voltages.

Before replacing the switching regulator IC [ICM801S: F9222L], check all the other components related to its other pins.  The most of the resistors and capacitors marked on this board will be SMD types [Surface Mount Types], and replacing them will be a challenging job. If this IC was found shorted, replace QM803 & QM802, even though they are found good.  Replace the opto-coupler Ic [PS803S:WK707] too. The most important thing to note is to check all the solder points in this section for loose soldering joints or dry soldering joints.  Resolder all the suspected solder terminals, by applying a little more solder. Check the solder terminals of the SMPS transformer [tm801] for loose contact.  Reconnect the unsoldered [RM801] back into circuit.

If everything is Ok. The set should switch ON without any problem.

In most cases, the solder terminals of  two regulator Ics used at the secondary side of the SMPS transformer was found loose solder points.  So check and resolder the older terminals of these regulator Ics [ICM853:KIA278R12P1 & ICM852:MC33167T]. 

When replacing components to power supply regulator section, insist on original type and number used.  Never make any experiment by replacing equalent or other types than specified.  It may make things more badly. 

On the 24VDC supply rail, which appears at pin number 1,2,3,4&5 of CNM802 & CNM803, should be checked for accuracy, as this is the main voltage that goes to the main board as well as the backlight inverter board.

If nothing can help you, or you feel difficulty in getting the exact component for replacement, it will be best to replace the power inverter board as card basis.

SAMSUNG LA26R71 LCD COLOUR TELEVISION: TROUBLESHOOTING AND REPAIR

PART – 4 

After desoldering out [QP810S:FCPH20L60 – MOSFET], and desoldering out one end of [RM801:0E22], the inserted fuse does not blow up, make sure that, all components on the section is OK.  Just Check the MOSFET for its Drain to Source leak. You can check it very easily with a multimeter set to Meg Ohms range.  The resistance in between Drain To Source must be very high, almost infinite.  If any leak found, replace the MOSFET. Just see, the rectified main DC voltage is fed to this MOSFET by the primary winding of [LP801], and the secondary of this transformer is again passed though one winding of starter transformer, and the other end of this winding of this starter transformer is rectified by [DF803:UF4007S] and smoothed by capacitor [CS806:68uF 65VDC], and supplied to the stand-by power switching opto coupler [PS801:WK707].  The secondary AC voltage actually generates from the secondary winding of [T801:Double Transformer].  This Double transformer is switched by MOSFET[QP801S] stated above.  If there must be a voltage with this secondary winding of transformer [LP801], the MOSFET and related circuit should work properly.  So this circuit can be considered as the main part of this power switching system.

If fuse does not blow up, even after MOSFET[D801S] has been replaced, check the voltage of all the pins [IC801S:4863G].  This is the booster section control IC.  This power supply is so designed to work with various inputs AC voltage levels, starting from 110VAC to 280VAC.

The main voltage selector function is controlled by this [IC801S].  The voltages of all the pins of this IC are

Pin –1 = 2.9V

Pin – 2 = 2.3V

Pin – 3= 2.9v

Pin – 4 = 0V

Pin – 5 = 0V

Pin – 6 = 1.9V

Pin – 7 = 0.5V

Pin – 8 = 16.4V [+ve supply]

Check this +ve 16.5V DC at pin number 8 of this IC.  If this is absent, check the resistance between this pins 16 to pin 6 of this IC.  It should never show very low Ohms measure.  If it shows very low resistance with an Ohmmeter, replace the IC.  It ahs damaged. Shorted.

Anyway, you have to first look fault at this section, with a dead set; because, this is the section that senses the input voltage, and determines to which voltage rating should be selected further to work.

Continued on Part-5

SAMSUNG LA26R71 LCD COLOUR TELEVISION: TROUBLESHOOTING AND REPAIR

PART – 3

We have already checked the MOV and found that it is good.  If so, the cause for power protection fuse may be due to some other reasons.  Before proceed, just unsolder one end of [RM801: 0E22Ohms] connected to supply the main switching regulator IC [ICM801S: F9222L].  This is the resistor supplies voltage to main power switching IC ICM801.  If this IC has internal short circuit, it will cause for blow up main fuse. Now unsolder out the sub power-switching transistor [QP801S:FCPH20L60].  This is a power MOSFET switching transistor that starts work first, as standby supply is derived from switching output of this transistor along with transformer [LP801].  If this transistor has shorted junction, will cause a tremendous current throug it to ground, which will cause fuse to blow up.

After disconnecting [RM801 & QP801S], just put a 5AMPS fuse in place in fuse holder, and switch ON the set by mains power on switch.  Look if fuse blows out now.  If this 5Amps fuse does not blow up, make sure that either main switching IC ICM801S or power switching MOSFET [QP801S] are faulty.  Check the junction resistance of QP801S for short.  If found short replace it with same type and number.  Be sure to replace this transistor with same number.

If fuse we inserted blows again as we switch on the set, with [RM801&QP801S] are desoldered out from the board, we have to check the components including main rectifier bridge, two line filter transformers [LX801S&LX802S] for winding short.  Check both the transformers by desoldering out them from the circuit board.  If found shorted, replace them.  There is no matter even one among them is not in place.  They are line filter, which prevents internal power supply switching oscillations from coming out to the main line back, and disturbing other electronic equipments.  There is no special function to these transformers, other than this. 

Check the capacitors, connected across the main AC power line, on board, [CX801X:330Kpf 250V & CX802S:330Kpf 250V] for short. Check [NT811S:NTC5D-15], connected in series to AC power line, in between line filter transformers [LX801S&LX802S].  

This is an NTC resistor [Negative Temperature Coefficient], connected in series with power line, to limit the tremendous current drawn by charging the main filter capacitor [CP803:150Uf 450VDC], when the set it switched ON each time by power ON/Off switch.  A wire wound resistor [4.7Ohms 7W], will also meet the need there.

If all these components said above are found good, again the fuse blows OFF as soon as the set is switched ON by its main power ON/OFF switch, the rectifier bridge is defective.  Replace it with same type and number.  Here again, insist on same type and number.

To be continued on part - 4

SAMSUNG LA26R71 LCD COLOUR TELEVISION: TROUBLESHOOTING AND REPAIR

PART-2

Let’s check fault to power supply board, step by step.

Consider the set is in dead condition.  No standby light on its front panel lights up.  No response main powers ON/OFF switch.

Check first the continuity or AC cord.  You can check it with a multimeter, set to Ohms range.  Check both conductor of the ac cord from plug point to the connection point to main power ON/Off switch for continuity.  If found faulty, replacing it must rectify the problem to your set.

If mains cord is found OK, check the contacts of the mains ON/OFF switch.  It is a DPST [Double Pole Single Throw] type switch.  If any one among its contact inside has trouble, main AC power won’t get into the set, causing a dead condition.

You can check the contact condition of the switch with the help of a multimeter, as we did to check the continuity of AC power cord earlier.

If Ac power cord, and Mains Power ON/Off switch are found OK, we have to troubleshoot the circuit board for proper working.

Be very careful while working with power board of any TVs, as mains power will be present there, when we switch on the set, and mains filter capacitor will hold a charge for a long time, which can hurt us.  Use of a hand glove is recommended when working with power boards.

Unscrew out the power board from the TV; Place it on a nonconductive surface

Inspect it.  It will have four output connectors [CNM 801, CNM 803, CNM 802 & CNM 804].  All these four connectors carries output voltages from this power board feeds other board of this TV. There will be an AC input point, to which AC is fed from two poles of the ON/OFF switch. Come to this point

There is a fuse [Over current Protection].  It is a 6.3Amps fuse.  Component number to this fuse will be marked as FS801S.  All component numbers will be printed on the power board, both on component side and print side.  From here, I’ll give you the components to be checked in a format [component part number on board: actual component number] hereafter.

Check [FS801S: 6.3AMPS FUSE].  If found blown up, make sure that some thing short circuit is there on the power board.  It should be due to some shorted component or components on board.  Check and find out this component/s is the main thing with repair.  Find out the exact point of fault, and exact component, which has got damaged.  Be very patient, careful and concentrate on work only. 

If mains fuse [FS801S] is found blown out, never insert a fuse to the fuse holder first.  Check the resistance across the [RX801X: 750K], which is connected across the AC input.  The multimeter should read high value resistance nearly 700KOhms here.  If it is found very low reading, say in Ohms value, Check [VX801X:INR10D751], for short.  Resolder this component out from the circuit and check its resistance.  It will look like a disc ceramic capacitor, it is not a capacitor.  It is a Metal Oxide Veristor [MOV], used as surge protector.  It is used with most of the present electronic device’s power supply section as a protection device.  It has a peak threshold voltage value, say 400VAC or so.  If any voltage spike appear with AC power line, over this threshold voltage, even for moment duration, the MOV will get shorted, resulting the mains protection fuse [FS801S] to bow out, thus protecting the device from further damages. In most occasions this will be the fault.  If MOV said above is found good [reading across its two terminals is very high; up to Megohms], we must go to check further

To be continued: on part-3

SAMSUNG LA26R71 LCD COLOUR TELEVISION: TROUBLESHOOTING AND REPAIR

LCD TVs are today’s’ most trend and they are slowly replacing picture tube based televisions, all over the world. Comparing to picture tube based televisions, these LCD or Plasma TVs are more venerable to faults, and are not long lasting.  More over, with LCD TVs, with lower frame rates are very troublesome to see the fast moving objects.  In most LCD TVs, this is a main drawback comparing to picture tube based TVs.  Fast moving objects will appear as jerking across the screen. With increased frame rate, this drawback can be rectified, but the cost of the TV will go high.

The repair work to LCD and Plasma TVs are very easy, comparing to picture tube based TVs, as only few replicable components are there on its boards. In most repair cases, board replacement should be done, as, there will be no replicable components, by normal disordering and soldering methods.  Mainly an LCD TV will have a main board, called “Logic Board”, which have most of the main functional, lie video processor, DDR RAM, main microcomputer, audio processor, audio output, sub microcomputer, tuner and memory sections.  Next to it, a video card, contains low voltage differential signal processor, multiple output regulator, dynamic random access memory, and two or more operational amplifiers and an EEPROM [Electrically Erasable Programmable Read Only Memory].

The third one to say is its backlight inverter card.  It will have a DC to AC converter, two comparators, four or more MOSFET [Metal Oxide Semiconductor Field Effect Transistor], used as outputs. This board in turn controls the backlight of the LCD TV.  According to the screen size, the number of backlight CCFL [Cold Cathode Fluorescent Lamp] lamps will increase, and the number of MOSFET outputs and CCFL drive transformers will be.  For a 26” LCD television, there will be at least 12 CCFL lamps.  This lamp driver board otherwise called as lamp inverter board is venerable to defect in most LCD TVs, irrespective of brand and model.  We can come to details later; now get a general idea about what are boards in an LCD TV, and their functions.

The fourth one is the main power board, which supplies all the power to other boards to work. The power board of different LCD brands has different circuits, but the output voltages comes from it will be almost the same.  Here I refer the circuit of SAMSUNG LA26R71.  A 26” LCD TV.

As stated earlier, there are mainly these four boards will be there for any standard LCD TV.  Some advanced models will have two more boards, which are used for surround sound output.

Let’s have a look at the power supply inverter board [SMPS] of the above said model.  I’m here to report some main faults I’ve got serviced.  So many other faults may occur, as a TV is composed of thousands of small components soldered together, each and every component in it has its own function when TV is switched ON.

To be continued: on Part-2

SONY KV HA21M50 _ KV HA21M80 _ KV HA21M81 _ KV HA21M80/H _ KV HA21M83 _ KV HA21P52 _ KV HA14M80

Fault:  No sound or distorted and low sound output from the speaker.

  Before do any thing, just check the settings first.  If sound MUTE is ON, there will be no sound from the output section.  Be sure it is in OFF state.

  The second step is to check whether you get audio signals.  To check this, plug-in a good headphone to the headphone socket.  If you do get sound by headphone, and not from the loudspeaker, make sure that the headphone socket has some trouble with its internal switchover contacts.  Just push in and take out the headphone pin into the headphone socket for at least five times, and check you get sound from the loudspeaker.

  If not, check the loud speakers for voice coil trouble.  You can check this without the help of a multimeter.  Take a good torch cell, and connect its two pole with two pieces of wire, and touch these wires to the terminals of the loud speaker.  If the speaker is good, you will hear a ‘Thumb’ sound for each intermittent touch with wires on the speakers’ connection tabs. If no sound is heard, be sure that the speaker I damaged, and should be replaced with same type.  Speakers’ impedance will be marked on its magnet.

If the speaker is found good, and there is no sound from it, even though you get sound output by connecting the headphones to its headphone socket, make sure that the headphone socket is faulty.  To replace it you have to disconnect it from the circuit, and buy a new one of same type.  It is a semiskilled work indeed.

If you can’t get any sound output from the headphone socket by connecting a good headphone to it, either the audio output IC do not get proper voltage, or may be defective.

  Audio output IC used with this set is [IC203] [AN 5276].  It is a dual amplifier type, that is, a single IC is used to amplify both stereo channel signals.  Even one channel amplifier stage inside this IC is defective; you have to replace the IC.

  It is a 12 solder terminal IC.  Check all the terminal soldering of this IC for loose solder points.  It is best to resolder all these solder terminals, by applying a little more solder, without making any solder short in between adjacent solder terminals.  Check the input voltage at [pin number 10] of this IC. If voltage is there, and even reordering terminals does not help you, replace the IC.  It is defective.

REMOTE CONTROL FAULTS

      SOME REMOTE CONTROLS WILL WORK PROPERLY AT DAY TIME, BUT NOT WORK DURING NIGHT TIME.

  Some energy saving lights may emit infrared signals, that can interfere with remote control signals to get an improper signal stream to TV, may make the main system control of the TV to be confused. If any energy saving lights is used in vicinity of the TV, turn them Off and check. 

If any Hi-Bright light ray from any other source hits the infrared sensor of the TV, it can also make malfunction.  Check whether any of such light sources near the vicinity of the TV.  If so, remove them and check.

  Universal Remote Control Codes, Setup procedure, Circuit diagrams and more ....

SETUP OR INITIALIZE CANNOT BE DONE WITH AN RM-TP501 REMOTE CONTROL

        To complete the setup, this remote control needs to be communicate with the receiver. Make sure that nothing other devices are connected with the receiver Via S-Link.  Check with nee batteries in the remote control.  Direct the remote control in frond of the display window of the receiver. Some type of fluorescent light rays will have negative effect on the ability of the receiver’s infrared sensor.  If such lights are there, switch them Off and check

SONY – KV 1985MTJ TRINITRON COLOUR TV

  No Extra High Tension voltage from LOT.  115VDC supply output from power regulator drops considerably.

Suspected components are FBT [Fly Back Transformer], Horizontal output transistor, Deflection Yoke, Capacitors connected with Horizontal output section. Especially check the free wheeling capacitor/s connected to the collector of the horizontal output transitor to ground, for leak.

Desolder out horizontal output transistor [Q802 – 2SB1877], and check it.  Check the junction resistance (collector to emitter) of this transistor.  In no case, it should be measured Zero.  There is an internal diode integrated with this transistor, connecting to its collector to emitter.  So, when you measure the resistors between collector to emitter of this transistor, consider the forward bios conductance of this Freewheeling diode. 

Replace the transistor with same type and number.

Switch ON the set after replacing this transistor.  Switch On for a short period of time, say for 5 seconds or so.  Switch the set Off and feel the heat of the replaced transistor by bare finger touch. It may be just warm, but not too hot.  If it overheats, check the associate components.  Suspect the FBT.  If FBT has a short in between its internal EHT windings, even a single winding short in between, will place a tremendous load to the fly back output transistor (2SB1877), and it will overheat.  If this is the case, there is no other way than replacing the FBT (NX-2821) with an other.  In most cases, (90%), the fault will be with a shorted winding inside the FBT; which cannot be detected with a multimeter.

Before replacing the FBT with an other one, just check the 115VDC of the switching power output for its accuracy.  Desolder out one end of resistor (R807 – 1.2 Ohms/2W).  All these component numbers will be marked on both sides of the printed circuit board of this TV. Desolder out any one end of this resistor, will cause a supply brake to FBT.  Connect a filament bulb (100 W), across (D608 – 120v Zener diode _ over voltage protection diode), and switch On the TV.  Measure the voltage across this Zener diode.  It should be between 113 to 117VDC.  If not, power supply regulator section has some trouble and should be tracked.  Never switch ON the TV without a constant steady B+ve 115VDC.  It may cause more complicated troubles to the circuit.

Universal Remote Control Codes, Setup procedure, Circuit diagrams and more ....

SONY TRINITRON – KV-1985MTJ

     Auto search tuning does not lock at all.  Indefinite auto searh. Auto tuning dose not stops or lock any stations in memory.

     Check the AFT signal at pin number [35] of IC 001 (M34302MB-612SP). Signal voltage to this pin comes from TUNER/VIF module (IF201 – IFD-380A).  Check the voltage at output pin number (6) of this IF module first.  If no voltage is there, check C202 (0.47uF) capacitor for leak.  If this capacitor has leak, it will short out the AFT voltage to ground, as it is connected to ground.  Replace it.  It will be best. Check R205 (33K) connected to positive 9V supply rail and AFT pin of the Tuner VIF pack for open.  If found defective, replace the resistor. Check C003 (0.001uF) ceramic disc capacitor soldered very close to pin number [35] of IC001 for leak. These are the only three external components to be checked for this fault.  If all of these are found OK, and still there is no voltage from AFT output pin from the Tuner VIF pack, make sure that the pack itself is faulty, and should be replaced with same type and number. 

     If AFT voltage is there, and still no tuning lock occur, check the voltage at pin number [36] of IC001.  It is the sync: voltage from LOT.  Must show about (0.7) volt.  If this voltage is not there, check (R029 – 33K) for open.  If this resistor is found OK, and still there is no tuning lock, make sure that (IC001-M34302MB-612SP – System Control Microprocessor) is defective.  Since there is no external memory chip is with this set, and the system memory is built inside the main system control IC, no more check must be done.