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Old 11-07-2019, 07:59 AM   #1
shelby5041
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Default TCL 55S401 LED LCD TV no backlight

hi

have this tv..powrs on fine and has image but no backlight

tested voltages at led backlight connected output cable and have 0V

removed led backlight cable and tested output again from PS and still have 0V

shouldnt i have voltage output if PS is good?

trying to figure out if ps is the issue or the backlights are the issue


thanks
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Old 11-07-2019, 08:01 AM   #2
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Default Re: TCL 55S401 LED LCD TV no backlight

oh and i do have BL on voltage which if i recall was about 3V
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Old 11-07-2019, 08:09 AM   #3
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Default Re: TCL 55S401 LED LCD TV no backlight

Some models will not turn the back light on if the MB sense a bad LED strip or Led. IF the MB is sensing an issue in the LED circuit you will not have voltage at the Back light connection. Since you have an image on the screen i would start by testing your back light LEd strips. More than likely one of them is faulty. Most of the time you can just bridge the faulty LED and the back light will come on due to the path now being bridged for current to travel through. Hope this helps.
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Old 11-07-2019, 09:03 AM   #4
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Default Re: TCL 55S401 LED LCD TV no backlight

hi beau

correct..however i removed the power cable to the led strips and i still get 0V output frpm ps ( this totally removes the backlights from the circuit so this should remove any backlight issues from the equation)

thats where im stumped

are you saying that the power supply will not output any voltage unless the led power cable is connected ?

Last edited by shelby5041; 11-07-2019 at 09:07 AM..
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Old 11-07-2019, 09:09 AM   #5
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Default Re: TCL 55S401 LED LCD TV no backlight

Quote:
Originally Posted by shelby5041 View Post
hi beau

correct..however i removed the power cable to the led strips and i still get 0V output frpm ps

thats where im stumped

are you saying that the power supply will not output any voltage unless the led power cable is connected ?
Yes most models will not output any power if not connected, now there is a way to manipulate the Main board into thinking the strips is connected. But from my past history i have always found that if the main board and power supply are coming on and you have an image with no back light then 95% of the time you have a faulty LED strip or LEd.
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Old 11-07-2019, 09:32 AM   #6
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Default Re: TCL 55S401 LED LCD TV no backlight

yes i agree almost all of the time its due to the failed led strip design

however im tyrying to rule out the power supply.and not just gusss.and it seems realitically there is no way to rule it out a bad ps?

removing the lcd panel to get to the led strips is not easy and can easily damage the panel..so i do not want to do that unless i know its the led strips 100%

i will wait for some more input before i remove the panel....i would think the ps would output voltages if cable disxconnected...the bl on voltage is present so it should output voltages if cable disconnected i would think...but you never know on these newer (smart) (dumb) tvs

Last edited by shelby5041; 11-07-2019 at 09:33 AM..
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Old 11-07-2019, 07:13 PM   #7
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Default Re: TCL 55S401 LED LCD TV no backlight

here is stock photo of power supply

i am trying to confirm that if the led backlight cable is not connected to the ps should i get voltage output from the ps or zero voltage at the led backlight pins?

im trying to rule out the ps as the issue.
Attached Images
File Type: jpg tcl55s401ps.jpg (1.08 MB, 15 views)
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Old 11-07-2019, 11:18 AM   #8
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Default Re: TCL 55S401 LED LCD TV no backlight

Lets see some good clear pictures of what we are dealing with.
Opening up the LCD panel is the LAST thing you want to do.
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Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956

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Inverter testing using old CFL:
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Last edited by budm; 11-07-2019 at 11:29 AM..
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Old 11-07-2019, 07:14 PM   #9
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Default Re: TCL 55S401 LED LCD TV no backlight

yes opening lcd panel is the last thing i want to do and that is what i have said...i only want to do that if im 100% sure its a led issue and not a ps issue

thanks bud
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Old 11-07-2019, 07:19 PM   #10
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Default Re: TCL 55S401 LED LCD TV no backlight

I need to see the pictures of the whole back side of the TV showing all the boards.
Right now I cannot tell how many wires are actually connected to the LED connector.

Last edited by budm; 11-07-2019 at 07:27 PM..
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Old 11-07-2019, 07:24 PM   #11
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Default Re: TCL 55S401 LED LCD TV no backlight

this best i can do..no space to get tv out of storage

i have 0voltages coming out from ps at the led backlight pins when led power cable disconnected

the stock photo may be wrong they have like 5 ps for this model tv..but my photos i just posted are actual photos
Attached Images
File Type: jpg GEDC4427.JPG (224.9 KB, 14 views)
File Type: jpg GEDC4426.JPG (231.9 KB, 14 views)

Last edited by shelby5041; 11-07-2019 at 07:26 PM..
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Old 11-07-2019, 07:30 PM   #12
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Default Re: TCL 55S401 LED LCD TV no backlight

sorry for the poor angles but no space here

yes my board is diff than the stock photo i posted earlier..i corrected myself in previous post
Attached Images
File Type: jpg GEDC4428.JPG (255.2 KB, 4 views)
File Type: jpg GEDC4429.JPG (240.3 KB, 7 views)
File Type: jpg GEDC4431.JPG (297.0 KB, 5 views)
File Type: jpg GEDC4432.JPG (238.6 KB, 7 views)

Last edited by shelby5041; 11-07-2019 at 07:33 PM..
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Old 11-07-2019, 07:26 PM   #13
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Default Re: TCL 55S401 LED LCD TV no backlight

Wait a minute here, your board is not the same as the board you show from shopjimmy!
What is the P/N as printed on the barcode sticker?

Last edited by budm; 11-07-2019 at 07:33 PM..
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Old 11-07-2019, 07:35 PM   #14
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Default Re: TCL 55S401 LED LCD TV no backlight

I cannot read the barcode sticker numbers.
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Old 11-07-2019, 10:11 PM   #15
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Default Re: TCL 55S401 LED LCD TV no backlight

Do you have about 380 ~ 400VDC reading between the two legs of the main filter CE1 when TV is turned on?
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Old 11-08-2019, 07:07 AM   #16
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Default Re: TCL 55S401 LED LCD TV no backlight

Correct me if im wrong but in his original post he states that the TV powers on and he as an image on the screen but no back light. IF this is correct wouldn't he have the 300-400VDC on the main filter caps?
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Old 11-08-2019, 07:16 AM   #17
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Default Re: TCL 55S401 LED LCD TV no backlight

hi bud beau
i appreciate all the help

i have tested all voltages at the 2 ps output connectors and they are all good except going to led backlights which is 0V

tv does power on fine and i have an image...just no backlight

and yes beau regarding LEd LCD tvs if there is no backlight most if not all of the time the issue is the failed led design and issue is bad led strips.....when an older ccfl style tv had no backlight it was almost always a PS/Inverter issue...and almost never a ccfl issue

new is not always better..its much easier changing out a board then it is changing out backlights ...people thing LED last forever lol...well in a perfect world they may however when there is a design issue they fail quickly as we have seen since the inception of cheap made junk made in china plastic constructed LED backlit tvs....its a horrible desgn...bring back CRT tvs..they were great durable...and lasted for many many years...

Last edited by shelby5041; 11-08-2019 at 07:25 AM..
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Old 11-08-2019, 07:35 AM   #18
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Default Re: TCL 55S401 LED LCD TV no backlight

Quote:
Originally Posted by shelby5041 View Post
hi bud beau
i appreciate all the help

i have tested all voltages at the 2 ps output connectors and they are all good except going to led backlights which is 0V

tv does power on fine and i have an image...just no backlight

and yes beau regarding LEd LCD tvs if there is no backlight most if not all of the time the issue is the failed led design and issue is bad led strips.....when an older ccfl style tv had no backlight it was almost always a PS/Inverter issue...and almost never a ccfl issue

new is not always better..its much easier changing out a board then it is changing out backlights ...people thing LED last forever lol...well in a perfect world they may however when there is a design issue they fail quickly as we have seen since the inception of cheap made junk made in china plastic constructed LED backlit tvs....its a horrible desgn...bring back CRT tvs..they were great durable...and lasted for many many years...
I agree 100% on bring back the old school CRT. They dont make them like they used to. Its more of a throw away and buy a new one world now.
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Old 11-08-2019, 07:18 AM   #19
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Default Re: TCL 55S401 LED LCD TV no backlight

what iv don in the past If you want to test the back lights circuit without any led strips connected is disconnect power supply cables from all other boards. Then either bring power supply on pin low or high depending on the circuit, check to see if you have all you dc voltage outputs EX 12, 5 24 depending on power supply. Then bring your Bl_on high by inserting 3vDC into the circuit and then you must bring your BL_dim circuit High with about 3VDC and that should activate the BL-On circuit and you should have a voltage across your pins on the connector. I wouldn't leave this circuit on for a very long time.

Just my 2 cents, not trying to step on tows here I to am learning as we all discus these things.
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Old 11-08-2019, 07:51 AM   #20
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Default Re: TCL 55S401 LED LCD TV no backlight

yes but thats what our gov wants here in the usa and many other countries..they want people to spend more money so they get more tax money...but gigantic issue almost noone talks about is where does all of this toxic junk go when its tossed out???..the common person think it magically just disappears ..our gov knows where it goes but they dont care because it wont affect them but it will affect future generatsion but like i said they dont care all they care about is tax dollars and making stuff that lasts for many years is not good for our gov pocketbook..and thats a fact....
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