Samsung UN55B7000WF - backlight present but no image

[northwestdad]

I recently picked up this set with the known problem that it would turn on but provided no picture. This was actually the TV in the conference room at my office so was rarely used. It had worked fine until a couple weeks ago when the video image failed. TV powers up as normal, backlight comes on and audio works, but no image on any of the inputs. I'm wondering if this sounds like an issue with the main board?

[budm]

Re: Samsung UN55B7000WF - backlight present but no image

It can be that the T-CON is not getting the 12VDC from the main board, or the fuse on the T-CON is blown, or the T-CON is dead even though the fuse and the 12VDC feeding it is OK, or the main board is not sending the LVDS to the T-CON.
So take good pictures of the backside of the TV so we can see how all the boards are connected together first. Do you have test equipment?

[northwestdad]

Re: Samsung UN55B7000WF - backlight present but no image

Sorry for the delay in getting back to this forum. I will take photos tonight and post them.

[northwestdad]

Re: Samsung UN55B7000WF - backlight present but no image

Here is a photo of the back of the TV. All capacitors look fine. The two black squares at the top left/right appear to be back-firing speakers, though it has down-firing speakers on the bottom. The whole TV is a little over an inch in depth. Also I do have a very basic voltmeter but my experience in using it, or any test equipment for that matter, is extremely limited.

[selldoor]

Re: Samsung UN55B7000WF - backlight present but no image

We also need pictures of the boards so we can see what to tell you to look at

We prefer just the thumbnails - not posted in line.

[Shinju]

Re: Samsung UN55B7000WF - backlight present but no image

I jut got the little bro to this unit, I got the UN46B7000. Posting a new thread but mine has a picture.

[northwestdad]

Re: Samsung UN55B7000WF - backlight present but no image

We also need pictures of the boards so we can see what to tell you to look at

We prefer just the thumbnails - not posted in line.

Will do. I did take some closeups of the boards, but they came out blurry and are fairly worthless. I'll take more when I get home tonight and repost.

I'm not experienced with uploading photos on this forum and took me 30 minutes of searching this morning before finally figuring out how to post the pic above.

[northwestdad]

Re: Samsung UN55B7000WF - backlight present but no image

Here are photos of the individual boards: Power, Main, and TCon (I presume).

[martino]

Re: Samsung UN55B7000WF - backlight present but no image

stole a better pic from shopjimmy for you from the T-con...

[budm]

Re: Samsung UN55B7000WF - backlight present but no image

White FUSE CF1 on the bottom left of the board with 'N' printing on top. Also check the voltage right at the CN505 (or 605?) at the pin with a white triangle which indicates as pin 1.

[northwestdad]

Re: Samsung UN55B7000WF - backlight present but no image

Are these the areas you mentioned? I know the pics weren't ideal. I also don't know how to test voltage or current or for shorts...meaning I don't know what im measuring for or what numbers I should expect to see on the multimeter readout.

[mscserbia]

Re: Samsung UN55B7000WF - backlight present but no image

Check that fuse.Set your multimeter on ohm position.

[selldoor]

Re: Samsung UN55B7000WF - backlight present but no image

Are these the areas you mentioned? I know the pics weren't ideal. I also don't know how to test voltage or current or for shorts...meaning I don't know what im measuring for or what numbers I should expect to see on the multimeter readout.

My opinion is that this is downright dangerous - you are trying to fix a TV with NO knowledge of electronics. There are voltages in a tv up to around 3000volts its not like changing a light bulb. Most people have prior knowledge of working on Pcs laptops or monitors before a TV project.
There are lots of videos and articles on the internet "how to use a multimeter"
would be a good start and "Recognising electronic components"
No instructions for your meter? - search the web "make model instructions"

When you KNOW how to use it and how to recognise components.
Do some tests to get used to holding the probes.

Suggest you only work on the open set when someone is in the house and
use a RCD

Anyway the fuse budm is talking about is in the picture posted by Martino

[northwestdad]

Re: Samsung UN55B7000WF - backlight present but no image

My opinion is that this is downright dangerous - you are trying to fix a TV with NO knowledge of electronics. There are voltages in a tv up to around 3000volts its not like changing a light bulb. Most people have prior knowledge of working on Pcs laptops or monitors before a TV project.
There are lots of videos and articles on the internet "how to use a multimeter"
would be a good start and "Recognising electronic components"
No instructions for your meter? - search the web "make model instructions"

When you KNOW how to use it and how to recognise components.
Do some tests to get used to holding the probes.

Suggest you only work on the open set when someone is in the house and
use a RCD

Anyway the fuse budm is talking about is in the picture posted by Martino

Thanks for the feedback and I did find the fuse and the white arrow on the TCon board. It's installed upside down on the unit so I couldn't find anything in the "bottom-left" when I looked initially.

And I do appreciate your safety message. I won't work on any sets that need to be plugged in while having their innards probed. I obviously don't have the knowledge to diagnose a board at the micro component level, much less repair it. I also know that some areas of the power board will retain electricity long after the unit has been unplugged, so I always wait several hours and usually an entire day before I start investigating. I have watched a few Youtube videos on multimeter use, but i quickly realized the risk of being electrocuted wasn't worth it. I have however "repaired" around 11 LCD and Plasma TVs since January for myself and a few friends, but most had something obvious wrong with them, like a bulged capacitor, blown fuse, loose fitting cables, etc. When the problem was immediately identifiable, the feedback that I received from the experts on this forum (and it has been amazing and greatly appreciated) was to help isolate the most likely cause, and then I just replaced the entire circuit board or sent it in for test/repair. I bought a multimeter mostly for looking for shorts, but have used it only once...however it did help isolate the problem and the TV now works perfectly.

I use ShopJimmy for replacement boards and have used ModusLink for board repair. All the capacitors I buy are through DigiKey and I tend to get the brands this site recommends if they're available. I can actually solder pretty good but don't have the right tools to handle surface mount components...another reason why micro-repair isn't an option for me.

Since most of the comments have focused on the TCon board being the issue, I'm going to order a replacement and see if that solves the issue.

Because I am always interested in understanding the "why" of something and know there will be other folks like me that have similar issues down the road and will find this thread, can you advise why you believe this particular issue is related to the TCon and not the main board? Is it because since the backlight and sound are working, but no image is present you presume the main board is working properly?

[martino]

Re: Samsung UN55B7000WF - backlight present but no image

I would wait a sec with ordering a t-con...
Theres a few easy steps you can measure to kinda be sure you are ordering (or repairing) the right board....
To check that fuse on the t-con is easy.TV OFF(unplugged),set multimeter on ohm scale,on beep mode is good(touch both probes of meter together,you should hear a beep) and put the red probe on one side of the fuse,the black probe on the other side of the fuse....do you hear a beep?Does the display read 0.3 ohm?
If fuse seems good(0.2 to 0.3ohm is good) then put the multimeter on DC 20 volts....
Now turn on the TV(careful,don't touch anything),put the black probe on the chassis of TV and put red probe on one side of that same fuse,read voltage on meter,put red probe on other side of fuse and read again...
Report back your findings

[northwestdad]

Re: Samsung UN55B7000WF - backlight present but no image

I would wait a sec with ordering a t-con...
Theres a few easy steps you can measure to kinda be sure you are ordering (or repairing) the right board....
To check that fuse on the t-con is easy.TV OFF(unplugged),set multimeter on ohm scale,on beep mode is good(touch both probes of meter together,you should hear a beep) and put the red probe on one side of the fuse,the black probe on the other side of the fuse....do you hear a beep?Does the display read 0.3 ohm?
If fuse seems good(0.2 to 0.3ohm is good) then put the multimeter on DC 20 volts....
Now turn on the TV(careful,don't touch anything),put the black probe on the chassis of TV and put red probe on one side of that same fuse,read voltage on meter,put red probe on other side of fuse and read again...
Report back your findings

OK...my multimeter advised that the fuse circuit is open (vs shorted) but there was no readout of any ohms...merely says open or shorted and beeps accordingly. Again...the unit beeped when the probes where touched together, but no beep when placed on either side of the fuse. I tried different settings under "Ohms" but nothing came back with any readings I then turned it to measure the volts, and grounded the black wire to the chasis and probed the red wire to both sides of the fuse as suggested (with the tv plugged in and my wife standing by ready to dial 9-1-1). The reading came back 0.0000 for both sides assuming I had the setting correct.

I've also included a pic of the multimeter I have. A simple $40 unit from RadioShack but I was told it was a decent if not minimalistic. The instructions are extremely basic as well and not a whole lot of help unless you want to check batteries.

[martino]

Re: Samsung UN55B7000WF - backlight present but no image

zero volts on either side of fuse seems weird... Was the tv turned ON or just plugged in?
TV will have to be ON in order to get voltage to t-con.
Also make sure that on your multimeter,it shows a solid line with dots underneath on the display when on volts,NOT a ~ symbol.

[selldoor]

Re: Samsung UN55B7000WF - backlight present but no image

Yes - i thought it odd too- easy test is set it on what you think is vDC and test a
battery AA AAA PP3 whatever.

If that reads the volts you are expecting the next place to test would be on the Connector
CN505 on the inverter board. Set powered up, meter on 20vDC - you see the five pins at one end between the two dark lines - they are all connected and it is the voltage feed from the main board. So black on chassis red on pin 3 say.
Also its sometimes only good using the chassis if the board is screwed hard down
otherwise put in one screw and black lead on the screw.

[martino]

Re: Samsung UN55B7000WF - backlight present but no image

I think the TV was sitting in standby,hence the zero volts....

[northwestdad]

Re: Samsung UN55B7000WF - backlight present but no image

I think the TV was sitting in standby,hence the zero volts....

Ummmm....yes. The TV was plugged in but not turned on.

I'll do so now and report back. I'll also try out the different pin locations per selldoor's comments