LCD TV Help !!! No Picture, Sound ok

maarksparky

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Hi all,

My sisters 46 inch Samsung LCD TV LE46M51B was working fine until the picture went black.. the sound is ok.. but there is no picture.. nothing on digital or analoug..

been reading stuff on the net as other folk have experienced the problem but there had been no replies..

any expereiences or suggestion as to what it could be ? please suggest

thanks in advance..
 

parker13

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Most likely to be the inverter board failing, can you see anything on screen if you shine a torch on it ?
 

digidude

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if it just suddenly went, normally on being turned on, then the fuse on the inverter board has gone m8, its just like turning the lights off behind the picture so you cant see it any more

'should' be a basic repair as long as nothing else has blown
 

maarksparky

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thanks digi.. you are a star bigman..

is it a quite easy job to do.. I do quite alot work myself so dont mind doing it.. where abouts is the invertor board ?? never opened an LCD before..

does it look like a capictor or one of the one fitted to the heat sink...

please advise..
 
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parker13

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From a lot of experience I have never known just a fuse to go open on an inverter board although it's possible, worth mentioning that the fuse will most likely be a surface mount device, it's normally one of the transformers failing, the inverter board will be on the side and have a transformer for each tube and two wires from each section where the transformers are that go to the very edge of the screen, sometimes I have known the transformers to go dry jointed so it's worth resoldering them, I would first check there are the necassary volts going to the inverter board, there will be a couple of capactors on the board, they should have about 24 volts on them, if they don,t it's not the inverter if they do it's the inverter board, with a digital multi metre you can compare readings from the transformers and figure out which one is faulty, the transformers arn't available as such but might be able to find a second hand one.
 

maarksparky

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thanks parker.. so just to get it right.. do I switch the lcd on standby to check the voltage or off ??

digidude any suggestions bigman ???

anyone got an idea what the fuse looks like ??
 

parker13

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Check for volt with the tv on and the sound working, should be about 24 volts on the caps at this point.
 

E74778

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Hi,

I have exactly the same problem with my Samsung LE46M51B LCD TV.

Going back to the question above, my TV has 6 boards inside as follows:

PCB down the LHS of the screen - 110 mm * 560 mm
PCB down the RHS of the screen - 110 mm * 560 mm
Main AV input PCB with all of the TV inputs on (190 mm * 190 mm)
Milano side auxiliary AV PCB (small board on the RHS from the back)
Main Power Supply PCB (240 mm * 330 mm)
LVDS board (170 mm * 110 mm)

The problem with my set is that when you turn the power on for around 1 to 2 seconds the screen lights up perfectly but then after that my screen goes black. During the 1 to 2 second interval I can hear the inverter running but as soon as the inverter stops the screen goes back to black.

I think I have an inverter problem but I don't know if it's situated on one of the PCB's or hidden elsewhere? My gut feel is that it's on the Main Power supply board but I am not sure.

One other point. You suggested measuring the voltages on the main power supply board, I have done this and all of the 5 VDC, 13 VDC Etc. voltage levels appear OK. However, all of the voltage references marked "VCC" are no where near the voltages stated on the test pads. Perhaps I am measuring against the wrong reference point; I am measuring these voltages to earth and with a standard Fluke meter.

I can obtain all of the PCB's off the net apart from the PCB's down the LHS and RHS of the TV.

Please could you advise me on where the inverter is and if you think this PCB is the problem (perhaps the Main Power Supply PCB?).

Hope you can help me with this one.

Ps, I have ordered a new 46" LCD TV so my currently faulty Samsung 46" TV will be going in the bedroom if I can fix it.


Thanks,

Alan.....
 

parker13

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Will get back to you in the Morn mate.
 

E74778

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Will get back to you in the Morn mate.


Thanks.

Rang Samsung and they say that it's almost certainly the power PCB, in fact the guy on the end of the line said it was 100% the power board but I would like a second opinion.

It looks like I will have to buy a power board in the near future, still like to here your expert opinion though!

Thanks,

Alan.........
 

davidh

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i had an inverter go on a smaller tv all i done was remove the board and reflow all the componants and it worked
1 of the joints must have been dry joint
worth a go
 

parker13

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Check you have 24 volts on the caps on the inverter board, if you have it's a safe bet you need a new inverter pcb, they can be repaired to component level,but if it,s not a transformer it's a long job, all you can do is check the transformers, they should measure about 1.5K on the secondary side, If you find a faulty one let me know, I might have one.
 

parker13

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On yours possibly down both sides, several transformers on them with two wires for each transformer going into the screen, be very carefull when checking for the 24volts and make sure it is unplugged when checking for around 1.5k ohms on the transformers, the inverter has very high voltage.
 

E74778

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Thanks,

24 transformers on each side on one PCB in two banks of 12 so thats going to be a long job, 48 transformers in total.

Q, if just one of the transformers has gone down or has a dry joint would just one section stop working because the inverter sound goes off for the whole screen after 1.5 seconds?

Sorry, I am becoming a pain now but I am learning about flat panel TV's fast!

Alan................
 

parker13

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If just one is faulty the whole lot shuts down, can you upload a pic, and also the part number of the inverters ?
 

E74778

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The part number for both boards is 120V46W2B Rev 13.

I have uploaded a picture of this board but because of the file size limitations it's not so good.

Strange thing is I can't open this image when it's on the forum, is it because I have have not posted often enough?

Alan.
 
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