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Start up problem.

No Picture and No Sound. Output of Bridge Rectifier reads 307VDC. The set uses a control IC, TDA4605-2 and a switching MOSFET Transistor, K1118 N-Cn in the SMPT and these components are OK. The Stanby LED light does not come on. The micoprocessor is not receiving a 5 volts supply. There's very little voltage, 57VDC ,on the B+ line. When power is switched on, a knocking or thumping sound ,on/off about once every second, is heard through the loudspeaker. This set is giving me a massive headache. Over to you top experts. Thank you very much.

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I suggest you look at the Horizontal output transistor, when it goes short the supply is in protection mode, it is pointless reading voltages at this stage, check the transistor located close to the Horizontal output (Flyback) transformer and normally mounted on a large heatsink. Check the caps in the primary power supply stage....hope that helps..Phil

Posted on May 19, 2009

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Posted on Jan 02, 2017

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2 Answers

Fuses keep blowing for my flat screen tv


Short circuited component/s at its main power regulator board. Contact any service technician. If you wish to get some details; check the site linked here. Viewing it in "Mosaic" will make surf easy.
http://electronicshelponline.blogspot.com/

Mar 16, 2014 | LG 42LC2D 42 in. LCD HDTV

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No sound, video OK in TVs


PICTURE IS OK AND THERE IS NO SOUND IN tvS

There are some occations arise when picture in a TV will be OK while absensce of sound.
Picure is OK, means that, functions from tuner upto video output, including power supply are OK. In most cases absence of sound may be with the fault to its speaker or speakers. In some sets there will be two speakers connected in series connection, and its sound output will be MONO. In these type of sets, if the connction is done as above, even one speaker has gone out [that is its voice coil or its connection gets opened, both speakers will not work]. In this case, you have to check each speakers individually for coil conitnuity, and the faulty one must be replaced. If there is no fault to the audio amplifier section of that TV, the problem will be solved with this.
In stereo sound system TVs, two of its speakers will have individual amplifiers, some may have both amps sections are integrated in one IC or two ICs are used seperately for each channel. In this type of sets, absenece of sound can be either to the fault of the failure audio output IC or its supply line voltage. In most cases, you can make sure the reason with a simple test without opening the set. Place your ear very close to its speaker side, and switch ON the set by its front panel power control switch. if a "Thumb' sound is heard form the speaker, you can confirm that the speaker is OK, and the power supply is comming to the output IC. If so, check the output IC terminal solderings for some loose contact. During long run, this may happen because, the Audio Output IC will heat up during working, and repeated heating and cooling may make loose soldering at its terminals; or a loose fixation of the IC to its metal heatsink, will relult overheating the IC. In most cases this is found a common fault. To rectify this, you have to open your TV, and pull out the audio output card, in some sets, this audio output section swill be built on the main board itself, place it upside down, and resolder all the terminals of the output IC by applying a little more solder, without making any solder bridges in between terminals of the IC. If this also doesn't help you, check the input voltage of the audio output IC. In most sets there will be a fuse resistor used as protection, will be in 0.2Ohms in value, and will get opend thus disconnect the supply; if IC has some fault. This will happen when the output IC itsef get shorted. If you see this resistor opend, check the output ICs positive supply rail terminal to the negative terminals' resistance with the help of an Ohm meter, if foud very low, say between 0 Ohms and 5 Ohms, make sure that the IC has got damaged. Here you have to repalce the IC and this fuse resistor too.
When replacing the audio output IC, make sure to apply thermal conductive paste, in between IC and it heat sink. This conductive paste can be bought from most of the electronic spare part selling shops at your town.
There is an other possibility too, is, the audio filtering stage in the video IF stage get faulty. To detect this, you have to go to the VIF section, and it is a skilled job, and the worker must have sound knoledge in electronics, and service experience.

on Mar 21, 2011 | Televison & Video

1 Answer

My Sharp TV's Stand-by Mode (Red), Model 14V-K80M, turns ON, turns GREEN when the other button is pressed but turns back to RED after a few seconds.


Hi

Your tv set may have an overload in the supply line. Check its rectifier diode and filter capacitor. Another approach is to check if the DC supply line of the switch mode controller IC (UC4842 for exemple).is present (10/12V). If these are OK, replace the switching MOSFET transistor and check the source resitor for open circuit.

Sully

Sep 21, 2013 | Sharp 27H-S60 TV

1 Answer

Philips 30PW My 30PW has no sound, it just stopped working while it was running. I have been through the menu 500 times and cant sort it out. Help!!


Hello
You haven't specified nothing about the condition of picture. Picture of your TV is good; and only sound has trouble, I assumes and posts this solution.
If picture is good and there is no sound output from its speakers, check first whether the sound mute function is on or off. It must be OFF condition to get sound from your TV. If it is in off position, and still there is no sound at all, just place your ear very close to the speaker powition of your TV and switch it ON by its front panel power switch, not by the remote handset. Check whether there is a 'thumb' sound is heard from the speakers. If it is there, speakers are OK and the sound output IC inside your TV is fauty, and should be replaced with same type and number.
If the sound detection section of your TV is faulty, there will be no sound. To detect this, connect your TVs audio out sockets at its rear side, to any external sound source like amplifier or so, and check the sound is there or not. If it is there, make confirm that the sound output IC itsef has failed.
Open your TV, locate the sound output section, pull out the printed circuit boar, and resolder most of the soldering points around the sound output IC, by applying a little more solder. If the fault was due to solder loose or bad soldlering, thie will rectify the fault. Keep attention to the pins of the IC while soldering, not to make any solder bridge short between them.
Also check the setting of sound system. If your TV is a multisystem one, make the system selection to auto, by surfing through its menu. If you wants furthermore assistance, get me through Fixya. OK.

Feb 28, 2011 | Philips Televison & Video

1 Answer

Hello, I am trying to fix the monitor LG L1951s that does not power on, I found the 68uF*450V capacitor bad, replaced this one but problem ramains. I have measured most of the componets on the power board...


The 68UF 450 is for the primay smps driving side, are you getting about 160vdc on that cap?
The PWM IC get the kick start DC voltage from the main bridge rectifier thorough a bunch of high resistance resistor to drop the 160vdc down to aboit 15vdc, once the PWM IC start working, one the winding will be the supplying the voltage to the IC to keep it running. If the DC output side detect short cirsuits (drawing too much current) it will go into shutdown, you need to find out if the inverter circuits has short circuits. The 5vdc and the 12~18vdc power supply will be running the minute you plug it in, you can solder in a 12v bulb at the DC output that feeds the inverter circuits (you can solder it directly on the DC filter caps for the 12~18 VDC filter caps of the inverter circuits). See application notes how this IC is used.
http://www.fairchildsemi.com/an/AN/AN-4129.pdf
http://www.fairchildsemi.com/ds/FA%2FFAN7601.pdf

No blown MOSFET on the primay side?
http://www.fixya.com/support/r5093881-lcd_flat_panel_tv_troubleshooting_guide

http://s807.photobucket.com/home/budm/allalbums

http://en.wikipedia.org/wiki/Capacitor_plague

Aug 21, 2010 | LG L1951S-SN (Silver, Black) (Black,...

1 Answer

I need MOSFET transisitor NF43AT , where I can found it.


That Mosfet is probably porprietory from Sports Art , But I would check the bridge rectifier I've had quite a few short out and make it appear that the Mosfet is shorted. Any of the Parts houses would carry that component.

Mar 12, 2010 | Sportsart 6300 Treadmill

1 Answer

Fuse is ok no 24v or other outputs


Your switched Mode Power Supply has failed... Check the output from the bridge rectifier, check the Controller IC, ALL the Electrolytic Capacitors, Do a "Dry" "Diode" multimeter test on all discrete components. Check for voltage on the pins of the DC side of the fly-back transformer too. Check for shorts.

Feb 05, 2010 | Protron PLTV-32 Television

1 Answer

Blows control fuse, have isolated power board, any ideas?


It can be shorted bridge rectifier, shorted MOSFET driving the switch mode transformer. Check those two parts first.

Nov 07, 2009 | Emerson LC320EM9 32 in. LCD HDTV

1 Answer

Power failer when switching on tv


A fuse blows when there is a fault and it is the first line of protection for the equipment. The fuse used in a typical plug is rated at 4A/220V. This means that a indeed fault does exist inside the equipment that is forcing it to draw a current greater than the rated. Almost certainly, the primary circuit of your Goodmans is at fault. If you are familiar with TV repair then check the bridge rectifier as well as the reservoir capacitor, with the switching semiconductor (BJT or MOSFET or IC) removed. If the fuse blows then the rectifier/capacitor are to blame. If not, then the semiconductor is at fault. If you are a novice, then rather refer servicing to a qualified tech since the risks outweigh the benefits.

Jan 09, 2008 | Televison & Video

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