# JVC LT-47EM59 Display Problem



## n9zez (Feb 26, 2010)

Hello,

Attached are a few photos of a problem I am having with a JVC LT-47EM59 (47" 1080p) that I just bought as is. I think I have narrowed the problem down to the mainboard or the LCD controller. Can anyone give me any pointers on how to determine which is faulty. Visually, both look just fine.

The first picture shows what the screen looks like when you first turn it on. After approximately 10 seconds, the tv displays, "No signal" on the screen. When the no signal message is displayed it is fuzzy looking.

I have checked all cables and everything appears secure. I have upgraded the firmware to no avail as well.

Your assistance is very much appreciated!


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## octaneman (May 13, 2009)

Hi n9zez


If you are comfortable with electronics, open the box and look if there are any capacitors that have bloated either on the main board or power supply. Replace as needed with proper values and re-assemble.


Note: Electronic equipment are sensitive and carry lethal voltages, if you don't know what you're doing have the screen repaired by a qualified technician.


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## n9zez (Feb 26, 2010)

Thanks for the quick reply!

I have visually examined all boards and cannot find any swollen or bulging capacitors. I don't have an ESR to check them in circuit either.


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## octaneman (May 13, 2009)

Use a DVOM to check the power supply, the vertical lines could be that it's missing the B+ somewhere on the circuit.


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## Done_Fishin (Oct 10, 2006)

Does it do that regardless of signal input ??


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## n9zez (Feb 26, 2010)

Done_Fishin said:


> Does it do that regardless of signal input ??


Yes, I get sound however the image looks similar to picture #1. 



octaneman said:


> Use a DVOM to check the power supply, the vertical lines could be that it's missing the B+ somewhere on the circuit.


How would I check this without a schematic?


Thanks for the prompt replies!


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## n9zez (Feb 26, 2010)

Took some readings from the power board in case it will help.


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## octaneman (May 13, 2009)

n9zez said:


> Yes, I get sound however the image looks similar to picture #1.
> 
> 
> 
> ...




You will have to follow the PCB trace from the secondary side of the transformer all the way to the molex connectors and take readings to all resistors, capacitors, transistors, that are on the pathway. You will have to check the voltages going to every pin on the molex connector, and then see if the voltages go from one board to the other board where the connector hooks up to. Then you repeat the trace readings across the other PCB board until you find an open or shorted component.



Note: This method is very time consuming and requires allot of concentration and patience, if you are tired or frustrated take a breather every 10 minutes or so to avoid personal injury and costly mistakes.


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## n9zez (Feb 26, 2010)

Octane,

You are thinking its more of a PCB problem than a mainboard or lcd controller problem?


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## octaneman (May 13, 2009)

I am thinking that the controller is not getting the B+ for it to do it's job, it's more along the lines of a transistor not switching on so the controller can lock in the 3.58MHz chroma signal.


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## octaneman (May 13, 2009)

Addendum:


After studying the chart you posted, on connectors A & C pins 1 through 5 all have 24 volts. This tells me that the power supply is not switching, giving 24 volts throughout the whole circuit board. From the picture I see 4 chips that look like photo-couplers. There is one next to the transformer, there are two next to the D connector, and another next to the C connector on the lower part of the board next to a transistor. I'm not certain if they are photo-couplers but the transistor next to it leeds me to believe it's the driver for it. If you can take the numbers off the chips then we would be able to verify that they are couplers. The purpose of the photo-coupler is to give pulses to the oscillator to start, they are usually connected from the output of the transformeron the feedback side. 



post back your findings.


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## Done_Fishin (Oct 10, 2006)

any black device straddling that thick white line (which is the isolation barrier between different SMPS circuits) and has 4 legs will most likely be an optocoupler.

Judging by the lack of components seen at the top of the board there must be a lot of smd components below on the solder side of the board.

I see no Integrated circuit for power control. neither do I see any voltage reference nor any potentiometer/ trimmer to regulate any voltage. There are insufficient capacitors for it to be self oscillating, as I have seen in some older TV circuits. I do see a lot of transistors/diodes on Heatsinks. but that board looks pretty bare to me and devoid of the basic controller elements.


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## n9zez (Feb 26, 2010)

Here are a few more pictures. You were right, lots more smd's on the bottom. Besides some large globs of solder, nothing looks bad.

The second picture is of the signal board. It seems to be modified. Is this factory?


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## n9zez (Feb 26, 2010)

octaneman said:


> Addendum:
> 
> 
> After studying the chart you posted, on connectors A & C pins 1 through 5 all have 24 volts. This tells me that the power supply is not switching, giving 24 volts throughout the whole circuit board. From the picture I see 4 chips that look like photo-couplers. There is one next to the transformer, there are two next to the D connector, and another next to the C connector on the lower part of the board next to a transistor. I'm not certain if they are photo-couplers but the transistor next to it leeds me to believe it's the driver for it. If you can take the numbers off the chips then we would be able to verify that they are couplers. The purpose of the photo-coupler is to give pulses to the oscillator to start, they are usually connected from the output of the transformeron the feedback side.
> ...


A & C go to the inverter boards. B & D go to the signal board. Forgot to add that.


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## n9zez (Feb 26, 2010)

Done_Fishin said:


> any black device straddling that thick white line (which is the isolation barrier between different SMPS circuits) and has 4 legs will most likely be an optocoupler.
> 
> Judging by the lack of components seen at the top of the board there must be a lot of smd components below on the solder side of the board.
> 
> I see no Integrated circuit for power control. neither do I see any voltage reference nor any potentiometer/ trimmer to regulate any voltage. There are insufficient capacitors for it to be self oscillating, as I have seen in some older TV circuits. I do see a lot of transistors/diodes on Heatsinks. but that board looks pretty bare to me and devoid of the basic controller elements.


This TV isn't very old. It was manufactured in Sept. 2008.


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## Done_Fishin (Oct 10, 2006)

n9zez said:


> This TV isn't very old. It was manufactured in Sept. 2008.


I wasn't implying it was .. I a just saying that I can't see anything on the board that reminds me of self-oscillating switch mode power supplies that I used to see in TV's of a few years ago.

One of the things that I see frequently is circuits, components & layouts that I have seen or worked on before. I used past experience to guide me through circuits. Quite frequently a device will be a mix'n'match of other circuits that are seen individually in several different devices. It's only when something new comes along that I must search for component data sheets in order to see how the component works.


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## n9zez (Feb 26, 2010)

Done_Fishing,

I wasn't trying to be accusatory, I was just letting you know when it was made.

I appreciate all of your guys help. What is your thought of picture #3 on my last post?

I am trying to decide which board to order and try. If I buy it from certain places I can return it if it doesn't fix the problem. Which board would you try first?


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## octaneman (May 13, 2009)

n9zez said:


> Done_Fishing,
> 
> I wasn't trying to be accusatory, I was just letting you know when it was made.
> 
> ...


 


The main board would be the first choice. IMHO the set does not exhibit the symptoms of an inverter board problem.


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## n9zez (Feb 26, 2010)

I never thought it was the inverter board. I was thinking either the main board or the LCD controller.


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## Done_Fishin (Oct 10, 2006)

I'd say it's toss up between the processor & the LCD display. I'd probably go for the processor board i.e. the board that holds the Video processor, purely because I have never encountered this sort of display on a display panel.


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