Samsung LN40D630 LCD TV, Backlights lit, but no display, please help

[sergio2013]

Backlights are lit, but no display, tested all voltages on the power supply and all check ok. no bulged capacitors, inverter ok since the backlights are lit. remote commands work as well as sound and the changing of the sources, but no image, tried unplugging the left ribbon for the panel on the t-con board and the whole screen turns white, then plugged the left one back in and unplugged the right one and the same thing a full white screen. plug them both in and screen is lit, but no image, just greyish black since screen is lit. Unplugged the power connector to the t-con board and same thing screen lit, but no image, just greyish black since screen is lit. Any ideas how to narrow it down?

[tom66]

Re: Samsung LN40D630 LCD TV, Backlights lit, but no display, please help

From the symptoms described I'd be looking into a T-con or panel fault.
This is a new TV only two years old!

[sergio2013]

Re: Samsung LN40D630 LCD TV, Backlights lit, but no display, please help

From the symptoms described I'd be looking into a T-con or panel fault.
This is a new TV only two years old!

Is there any way to test the t-con?

[tom66]

Re: Samsung LN40D630 LCD TV, Backlights lit, but no display, please help

You would need a scope to trace signals, beyond checking voltages on some points.
Can you post a picture of your T-con?

[sergio2013]

Re: Samsung LN40D630 LCD TV, Backlights lit, but no display, please help

You would need a scope to trace signals, beyond checking voltages on some points.
Can you post a picture of your T-con?

Sure here is a picture of it. You don't think it could be the main board?

[tom66]

Re: Samsung LN40D630 LCD TV, Backlights lit, but no display, please help

Some places to check

VGH: +20V to +30V
VGL: -5V to -10V
Not shown AVDD: 15V
Not shown VCOM: 1/2 AVDD
VGMA area: Voltage from GMA_1 thru GMA_NN should increase from one to the other, or decrease from one to the other, but not both.
Voltage regulator as described elsewhere.

Unlikely to be main board due to having audio, rare for main board to fail to output video and still give audio.

[sergio2013]

Re: Samsung LN40D630 LCD TV, Backlights lit, but no display, please help

Some places to check

VGH: +20V to +30V
VGL: -5V to -10V
Not shown AVDD: 15V
Not shown VCOM: 1/2 AVDD
VGMA area: Voltage from GMA_1 thru GMA_NN should increase from one to the other, or decrease from one to the other, but not both.
Voltage regulator as described elsewhere.

Unlikely to be main board due to having audio, rare for main board to fail to output video and still give audio.

Ok, ill test those tonight as now I don't have time, then ill post back, I find it odd that when I unplug the ribbons that go to the panel from the t-con one at a time that the whole screen turns white, isn't one ribbon controls one half and the other ribbon controls the other half? shouldn't only half the screen turn white when I disconnect one ribbon at a time?

[tom66]

Re: Samsung LN40D630 LCD TV, Backlights lit, but no display, please help

Some LCD panels operate in the "normally lit" mode, that is, without power, they allow light to flow through. So it sounds like the T-con is powering the panel but keeping the panel in the normally dark mode -- pixels turned on to block light.

[sergio2013]

Re: Samsung LN40D630 LCD TV, Backlights lit, but no display, please help

Some LCD panels operate in the "normally lit" mode, that is, without power, they allow light to flow through. So it sounds like the T-con is powering the panel but keeping the panel in the normally dark mode -- pixels turned on to block light.

So what your saying is the problem is most likely the T-Con board correct? I don't think its the panel, I took the frame off the panel and pressed on all the tabs along the sides and they seem very good. I tested the voltages on the T-Con and it looks ok for the voltages, but may have an issue with the data, don't have an scope to test the data busses. I just hope that I choose the right board to replace because im afraid if it may be the main. I know you said if it responds to the remote commands, buttons in the front, changes sources and accepts HDMI signals and also plays the sound that its rare for it to have sound, but not video, but isn't the sound processor separated from the video GPU? it looks to have a Realtek sound IC.

[tom66]

Re: Samsung LN40D630 LCD TV, Backlights lit, but no display, please help

Please post your GMA voltages.

The Realtek IC is possibly the DAC for the sound -- i.e. generating the analog signals. However, the actual processing of the audio (decoding from HDMI, decryption, effects like fake surround sound / dolby) happens on the main processor before being sent to the sound chip. Though, it is more likely the Realtek IC is the ethernet controller as Samsung like to use Realtek chips for that (these TVs run Linux and the Realtek chips are readily supported by the Linux kernel.)

[sergio2013]

Re: Samsung LN40D630 LCD TV, Backlights lit, but no display, please help

Please post your GMA voltages.

The Realtek IC is possibly the DAC for the sound -- i.e. generating the analog signals. However, the actual processing of the audio (decoding from HDMI, decryption, effects like fake surround sound / dolby) happens on the main processor before being sent to the sound chip. Though, it is more likely the Realtek IC is the ethernet controller as Samsung like to use Realtek chips for that (these TVs run Linux and the Realtek chips are readily supported by the Linux kernel.)

Yes you are correct because the Realtek IC starts with RTL which stands for Realtek LAN. I tested all other voltages other than the GMA voltages as I do not know where to test those. I attached a better picture.

[tom66]

Re: Samsung LN40D630 LCD TV, Backlights lit, but no display, please help

Here; test points marked GM1 thru GM18, as well as others, corresponding to the nearby legend.

[sergio2013]

Re: Samsung LN40D630 LCD TV, Backlights lit, but no display, please help

Here; test points marked GM1 thru GM18, as well as others, corresponding to the nearby legend.

Ok here are the results


GMA 1 = 17.04

GMA2 = 14.01

GMA3 = 13.26

GMA4 = 12.43

GMA5 = 12.11

GMA6 = 11.69

GMA7 = 11.33

GMA9 = 9.73

GMA10 = 8.22

............

GM1 = 16.97

GM2 = 14.04

GM3 = 13.26

GM4 - 12.42

GM5 - 12.11

GM6 = 11.72

GM7 - 11.33

GM9 = 9.77

GM10 = 8.20


.....................................................................................................................................


GM12 = 6.61

GM13 = 6.152

GM14 = 5.664

GM15 = 5.256

GM16 = 4.295

GM17 = 3.415

GM18 = 0.273

.............

GMA 12 = 6.62

GMA 13 = 6.195

GMA 14 = 5.651

GMA 15 = 5.232

GMA 16 = 4.287

GMA 17 = 3.445

GMA 18 = 0.205

[speedypro]

Re: Samsung LN40D630 LCD TV, Backlights lit, but no display, please help

Is there any way to test the t-con?

This a gold tip for you. Look on your T-CON board and look for the "P" fuse. It's very tiny. Those are notorious to blown. I guarantee you have a bad one. Or just look for the main fuse and test it.

[sergio2013]

Re: Samsung LN40D630 LCD TV, Backlights lit, but no display, please help

This a gold tip for you. Look on your T-CON board and look for the "P" fuse. It's very tiny. Those are notorious to blown. I guarantee you have a bad one. Or just look for the main fuse and test it.

I checked and I don't see anything with a P, but I see one with a N labled C_DF1 and its white. is that it? I did a Ohm check on that part and my multimeter is telling me its shorted.

[tom66]

Re: Samsung LN40D630 LCD TV, Backlights lit, but no display, please help

Since you have voltages across the T-con, the fuse isn't blown. The gamma voltages are good. I would replace the t-con as a first step as you cannot really diagnose further without a scope.

[sergio2013]

Re: Samsung LN40D630 LCD TV, Backlights lit, but no display, please help

Since you have voltages across the T-con, the fuse isn't blown. The gamma voltages are good. I would replace the t-con as a first step as you cannot really diagnose further without a scope.

Ok will do and report back when the new T-Con arrives. Thanks for your help.

[speedypro]

Re: Samsung LN40D630 LCD TV, Backlights lit, but no display, please help

I checked and I don't see anything with a P, but I see one with a N labled C_DF1 and its white. is that it? I did a Ohm check on that part and my multimeter is telling me its shorted.

My bad. Yes if you have voltage across the board then fuse is ok.

[sergio2013]

Re: Samsung LN40D630 LCD TV, Backlights lit, but no display, please help

Since you have voltages across the T-con, the fuse isn't blown. The gamma voltages are good. I would replace the t-con as a first step as you cannot really diagnose further without a scope.

Just got the T-Con board put it in and bam the TV is working, so it was the T-Con board that was faulty. Thanks for all your help guys.

[tom66]

Re: Samsung LN40D630 LCD TV, Backlights lit, but no display, please help

Glad to hear! Enjoy your TV.