TCL 55S401 LED LCD TV no backlight

[shelby5041]

Re: TCL 55S401 LED LCD TV no backlight

update beau and bud

BBBBBBBBBad news

i reluctantly removed the lcd panel....since i have damaged several in the past

it was indeed 1 bad LED strip..unfortunately during my swapping out etc trying to isolate the bad led i fried my power supply

thats actually the not so bad news....even worse , i cracked the LCD panel while handling

i hate removing lcd panels and may consider not doing it anymore as it wastes a lot of time and the risk just isnt worth it

thanks for all your help

[shelby5041]

Re: TCL 55S401 LED LCD TV no backlight

hi bud and beau i havent done any further testing busy with other things.. today though i brought tv in from garage and powered on and i can see the TCL logo light up for a fraction of a second and then backlight powers off (im thinking shutdown due to bad led) ... previously i tested outside and could not see this due to ambient light....so now i thinking that it is indeed a led issue and that this tv does not output power to the conne3ctor unless bacjklights plugged in and good...since replacing ps produced same results im pretty confident 99% that its bad LED which is what is normally the issue on most LCD LEd tvs when no backlight...the ps is typically not the issue.....in the old days with CCFL it was opposite..it was mostly ps/inverter issue and almost never lamp issue....most vifdeos have shown you shoyuld have voltage to the backlight connector even with backlights disconnected but apparently on this model that is not true since i have 0V with connector disconncted and yes bud maybe i was not testing the voltages at exact time in order to see the initital voltage(with BL connected) since its powering on only for a fraction of a second...all i do know is with connector disconnected to BL i have 0v and BL signal on.

[Beau28713]

Re: TCL 55S401 LED LCD TV no backlight

Curious as to what you have found out?

[budm]

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.

[shelby5041]

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

[Beau28713]

Re: TCL 55S401 LED LCD TV no backlight

That would be a good assumption.

[shelby5041]

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?

[shelby5041]

Re: TCL 55S401 LED LCD TV no backlight

i have BL on voltage also

[shelby5041]

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...

[Beau28713]

Re: TCL 55S401 LED LCD TV no backlight

Any update on the voltage budm was asking about? Did you get it repaired?

[h_smith]

Re: TCL 55S401 LED LCD TV no backlight

Sorry, wrong thread again. Geeze, sorry.

[budm]

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.

[h_smith]

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.

[Beau28713]

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.

[Beau28713]

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.

[shelby5041]

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

[shelby5041]

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

[Beau28713]

Re: TCL 55S401 LED LCD TV no backlight

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.

[Beau28713]

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.

[shelby5041]

Re: TCL 55S401 LED LCD TV no backlight

beau i have all voltages at the ps connector including BL on voltage