Toshiba 55lf621c21 Dim Picture / Backlight afterbypassing a Burnt LED

[willis6732]

Hello,

This TV came in for a backlight Repair. I bypassed the Burnt LED as shown in Picture. I thought it was fixed and returned to customer. So I dont have the TV anymore, but customer says its not really watchable.

Now the TV Is much dimmer than before. It does a quick bright flash when it first turns on.

The Driver board looked pretty toasty in the LED Driver Area.

So I am wondering.. how can i Tell if this is a LED or Driver Board Issue?

[Diah]

are you calling what you did was repair or fix? how about if there are Zener diode build in LED unit... what about currents to calculated how many LEDs build in..... how much you charged him LOL

delete please yours photo before other things who are here to repair are cheat persons

[willis6732]

Holy symantics. Looking for help, not to be critisized about life. Not sure how to delete photo. Edit button is gone. Yes ive fixed many TV's with this method. Got the Method from Electronics repair school channel if you want to critisize sorin. If you dissagree with anything i did, just state the correct method. Jeese

[Diah]

Holy symantics. Looking for help, not to be critisized about life. Not sure how to delete photo. Edit button is gone. Yes ive fixed many TV's with this method. Got the Method from Electronics repair school channel if you want to critisize sorin. If you dissagree with anything i did, just state the correct method. Jeese

you called my post to you as criticized, however the answer was include it...
Zener diode build in ------- test one working LED unit if there zener diode build in reserve way .. yes need to replace all as the value of the zeners got changed to low or high over all other LEDs
currents measurement -------- measure the pulling V at start up from cold state--- if its pull high and then reduced ... if yes then replace all strips

[willis6732]

Zener diode build in ------- test one working LED unit if there zener diode build in reserve way .. yes need to replace all as the value of the zeners got changed to low or high over all other LEDs
currents measurement -------- measure the pulling V at start up from cold state--- if its pull high and then reduced ... if yes then replace all strips

Well sorry if ive posted dumb misleading information.
Thanks for the help on diagnosis LED Strips. THis is valuable information i was unaware of. Could you please clarify some things before a get the TV back here...

"currents measurement -------- measure the pulling V at start up from cold state--- if its pull high and then reduced ... if yes then replace all strips"
So i should check for voltage droping on backlight circuit. Im assuming to use High mode on Voltmeter? What is an acceptable voltage fluctiation 1V, 5V, 10V ??

I also dont understand how to tell if a LED has a zener diode in it.
"Zener diode build in ------- test one working LED unit if there zener diode build in reserve way"
How do i perform this test? Just with Diode mode? What is an acceptable reading?


Ive attached a pic of the Driver board. The small coil or Choke at the very top toward the right next to the two electrolitic caps is the area that was very toasty looking. Wondering if this is an area of concern....

[Diah]

zener test .. use diode mode of yours DMM. in way the fine LED will light on dim... and if you put the probe in reserve way... if there are zener you will have 0.65-0.75 dropping on your DMM... if there are nothings need to test another LED to be sure same value so if nothings then no zener build in

dropping current... but your DMM on 250V DC with refrence to TV chassis put the red probe on LED+ at the socket of BL on PSU.. then turn on.... you will have high and low reading

[EazyBone]

This is a fix for your own tv.. not a customer. Replace the lights fully.

[willis6732]

zener test .. use diode mode of yours DMM. in way the fine LED will light on dim... and if you put the probe in reserve way... if there are zener you will have 0.65-0.75 dropping on your DMM... if there are nothings need to test another LED to be sure same value so if nothings then no zener build in

dropping current... but your DMM on 250V DC with refrence to TV chassis put the red probe on LED+ at the socket of BL on PSU.. then turn on.... you will have high and low reading

Thanks. I havnt dealt with zener LEDs before. I didnt know DMM could be used on them

I dont have the TV with me, and i did find the LEDs from china for $36 so i went ahead and orderred the out of my pocket

I will report back with BL output wheni get the LEDs


PS. I am brutally honest with customers and they know as much as i do about the validity of the repair.

[willis6732]

Hello, I received replacement LED strips and wanted to give an update on those

In Diode mode the LEDs light up one direction and OL in the other direction. So by your explaination im guessing they are not Zener.

Except one of the LEDs doesnt light up with diode mode and reads .2 to .3 each directions.

But with the LED tester that LED lights up normally.

Each LED strip x8 shows 15V on my LED Tester. I tried shorting the one weird LED for fun and Voltage goes to 12.3V for the strip

Wondering, do i just ignore the LED with the weird diode readings since it seems to be functioning ok?? hrmmmm

More updates when i Get the TV here.

[Diah]

Hello, I received replacement LED strips
Except one of the LEDs doesnt light up with diode mode and reads .2 to .3 each directions.

take this complete out from strips and find one with lens from old one. cut it .. and stick it in place and jumper - + to the bad led rails.

[willis6732]

The TV brightness has returned to normal with all the LEDs working.

I have some dark mark in the lcd from suction cups. are suctions cups ok to use? Maybe mine are too strong?

[EazyBone]

What cups do you have? Super strong ones aren't recommended.. I'm sure you tried wiping it down with cloth and water.. sometimes I got to put some gentle elbow grease into it and it will come off. But I think it's dirt in my case.

Also I assume you changed all the LEDs and that fixed it

[willis6732]

What cups do you have? Super strong ones aren't recommended.. I'm sure you tried wiping it down with cloth and water.. sometimes I got to put some gentle elbow grease into it and it will come off. But I think it's dirt in my case.

Also I assume you changed all the LEDs and that fixed it

Yes replacing the LED fixed the dim light display issue.


What do you mean elbow grease? Like actually massage the LCD in a buffing motion? Would be funny if you were pulling my leg and got me massaging the tv.


I didnt really rearch much when buying my suction cups. I went for bigger. The seems very heavy duty. lol
https://www.amazon.ca/dp/B0D1FSZXHL?...sin_title&th=1

Any recomendations for suction cups?

[EazyBone]

Oh my lord those are way too heavy duty.. although maybe if you didn't pump too much it would of worked. I use these

https://www.harborfreight.com/4-23-i...8aAmK7EALw_wcB

One for each hand, I've done up to 82 by self so they work well

I mean generally the rubber leaves a mark in a circle on the screen so a microfiber cloth and a small spritz of water and sometimes you got to rub it to get the circle out. After seeing those cups though, you may have put that into the screen.

But it may just be able to be rubbed out. Don't press super hard but you gotta use some elbow grease.. very slight pressure into the cloth and see if any gets removed and if it starts to the massage that S.O.B until it's good

[willis6732]

Oh those suction cups look great. Thanks

TO clarify, its the LCD panel that has dark circles in the LCDs themselves. Its not marks on the surface of the screen. I got those out pretty easy with some iso.

[petehall347]

I didnt really rearch much when buying my suction cups. I went for bigger. The seems very heavy duty. lol
https://www.amazon.ca/dp/B0D1FSZXHL?...sin_title&th=1

i use very similar ones to pull dents out of car bodywork

[EazyBone]

Yes you moved the liquid around probably. Too strong

[willis6732]

Well so much for that. This was the TV today.... Thanks everyone