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Old 11-08-2019, 07:35 AM   #21
Beau28713
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Default Re: TCL 55S401 LED LCD TV no backlight

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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, 07:51 AM   #22
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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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Old 11-08-2019, 07:53 AM   #23
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Default Re: TCL 55S401 LED LCD TV no backlight

beau i have all voltages at the ps connector including BL on voltage
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Old 11-08-2019, 07:58 AM   #24
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Default Re: TCL 55S401 LED LCD TV no backlight

one of my hobbies is I go down to our local dump where they have a bin for all electronic disposal, I root around and find units to repair or steal parts off of. I have supplied my brothers, my fathers, and my house all with 50 inch plus tvs that i have repaired. I think so far the most i have in one tv is about 50 bucks. Ill try and fix anything i can find!! its fun for me. I also fix stuff up and sell it for just what i have in parts to people that need things that cant afford new stuff.

Last edited by Beau28713; 11-08-2019 at 08:00 AM..
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Old 11-08-2019, 07:59 AM   #25
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Default Re: TCL 55S401 LED LCD TV no backlight

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Originally Posted by shelby5041 View Post
beau i have all voltages at the ps connector including BL on voltage
In my experiences The bl_dim has to be there also, if its not the power supply thinks the back lights needs to be off.
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Old 11-08-2019, 08:05 AM   #26
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Default Re: TCL 55S401 LED LCD TV no backlight

hi beau..thats awesome..saving landfill is what everyone should do..but todays society just dont care...i basically will not fix a tv if it costs more than about $25...since they have little to no value anymore....if i cant fix for 25 or less i just tear it apart and sell the parts to someone who wants to fix their tv...i cant see spending more than 25 when the tv is only worth $50 fixed lol..out here where i live used lcd tvs sell for $50 or less

Last edited by shelby5041; 11-08-2019 at 08:08 AM..
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Old 11-08-2019, 08:09 AM   #27
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Default Re: TCL 55S401 LED LCD TV no backlight

what voltage value should i have at BL=dim? i can check later..but i beleive i had all voltages at the pins on the ps connector
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Old 11-08-2019, 08:11 AM   #28
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Default Re: TCL 55S401 LED LCD TV no backlight

I normally limit myself to $50 or ill find a buyer first and ask them if it is fixable how much would they be willing to spend on the repair. I never charge labor fees only parts. I sold one 50 inch plasma to a lady for .50 cents. lol. she was so happy she hugged me for like 10 mins. lol
I try to give back to the world as much as i can. MY day job is a Electronic engineering Tech. We mainly work on government contracts aircraft electronics.

Last edited by Beau28713; 11-08-2019 at 08:15 AM..
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Old 11-08-2019, 08:13 AM   #29
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Default Re: TCL 55S401 LED LCD TV no backlight

If i remember correctly the BL_dim should vary from low DC voltage close to zero bl off up to maybe 4VDC BL full on.
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Old 11-08-2019, 08:53 AM   #30
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Default Re: TCL 55S401 LED LCD TV no backlight

Posted on wrong thread. Please delete this as I cannot find the option to delete it myself.

Last edited by h_smith; 11-08-2019 at 09:00 AM..
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Old 11-08-2019, 10:53 AM   #31
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Default Re: TCL 55S401 LED LCD TV no backlight

So do you have 380 ~ 400VDC or not? The backlights circuit needs that PFC Boosted Voltage to work.
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Old 11-08-2019, 03:17 PM   #32
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Default Re: TCL 55S401 LED LCD TV no backlight

Sorry, wrong thread again. Geeze, sorry.

Last edited by h_smith; 11-08-2019 at 03:20 PM..
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Old 11-13-2019, 07:16 AM   #33
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Default Re: TCL 55S401 LED LCD TV no backlight

Any update on the voltage budm was asking about? Did you get it repaired?
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Old 11-13-2019, 05:52 PM   #34
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Default Re: TCL 55S401 LED LCD TV no backlight

hi sorry not able to do any further testing....we got tons of snow and tv is in garage can not get to it....like i said the tv powers on fine with sound and picture but no backlight voltage at all 0V....i have all voltages coming out from the power supply to main board...
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Old 11-13-2019, 05:52 PM   #35
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Default Re: TCL 55S401 LED LCD TV no backlight

i have BL on voltage also
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Old 11-13-2019, 05:54 PM   #36
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Default Re: TCL 55S401 LED LCD TV no backlight

and ...i did buy a used power supply and same exact results....so that would tell me backlights are bad and that indeed this tv model does not output voltage from ps to backlights unless connected and good...would that be correct?
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Old 11-13-2019, 05:57 PM   #37
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Default Re: TCL 55S401 LED LCD TV no backlight

That would be a good assumption.
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Old 11-13-2019, 06:10 PM   #38
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Default Re: TCL 55S401 LED LCD TV no backlight

yes as it would be extremely rare to have 2 power supplies with exact same issue so i have to assume on this particular tv..the standard check for voltages is null and void to rule out the power supply ...and the fact that when there is a LED backlight issue its 95% of the time bad backlights and not bad PS even more points to my issue being bad LEDS

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Old 11-13-2019, 09:29 PM   #39
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Default Re: TCL 55S401 LED LCD TV no backlight

Bad backlights you still should have Voltage at the LED connector BEFORE it goes into shutdown if it detects bad backlights, and we still do not know if you even have Dimming control signal or not beside the PFC Voltage.
Also try this test: TV is OFF then keep the DC meter probes on L2+ and L2- then turn on the TV to see if the Voltage even jumps to over 100VDC or not, repeat the same test on L3+ and L3-.
you can also spend about $30 for LED tester.

Last edited by budm; 11-13-2019 at 09:45 PM..
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Old 11-22-2019, 03:21 PM   #40
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Default Re: TCL 55S401 LED LCD TV no backlight

Curious as to what you have found out?
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