Re: Insignia NS-55D420NA16 Backlight Problem
When measuring the LED voltage you put your black probe on Chassis earth and measure on the RED wire (Anode). According to what i read on this post the voltage should be around 200VDC. You probably have an "open" LED and that's why the voltage spikes at 400V.
Take great care when opening the panel as to not break the screen. My experience is almost every time i had a problem like this it turned out to be backlight LED's that had failed.
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Re: Insignia NS-55D420NA16 Backlight Problem
**First post** Man that sucks. I have the exact same TV but when I check my red/white wires going to the LEDs I get a spike of a little over 400DCV then back to almost 0DCV. I am trying to remember if that was across the red/white or red only and to chassis for ground. (it's been a few weeks) My backlights do not even flicker. With the red/white wires unplugged I get 0DCV on both pins. My voltages on my 10 pin output are the same as yours. Not sure if I should order the LED tester or if it is the LED driver on the powerboard. Anyone have any suggestions for a newbie? ThanksLeave a comment:
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Re: Insignia NS-55D420NA16 Backlight Problem
Shit happens. Even to some of us who should know better. Don't worry as this exercise is not a total loss. You learnt a few things in the process. Cheer up.Leave a comment:
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Re: Insignia NS-55D420NA16 Backlight Problem
I might need the strips from this. Let me know if you're selling.Leave a comment:
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Re: Insignia NS-55D420NA16 Backlight Problem
yeah rather broken.
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Re: Insignia NS-55D420NA16 Backlight Problem
Ok update. So I got everything to power up but unfortunately I think I damaged the panel itself during the process. I'm posting a picture so one of you can confirm my diagnosis. So close!Attached FilesLeave a comment:
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Re: Insignia NS-55D420NA16 Backlight Problem
Ok so I replaced the LED strips and tested them with my tester and they all light up. I reassembled the filters and the panel and tried testing it and now I get no picture or backlight whatsoever. I checked for voltage on the led connector from the power supply board and there is no voltage there. At one point in my testing I touched something on the power supply board and got shocked. I'm wondering if I somehow damaged it. Any thoughts before I replace the board?Leave a comment:
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Re: Insignia NS-55D420NA16 Backlight Problem
Take the Voltage reading using the your LED tester when you have new LED strips installed so we can see what the total Vf of the LED string is.
So you have lots of shorted out LED's.Last edited by budm; 06-26-2018, 11:03 PM.Leave a comment:
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Re: Insignia NS-55D420NA16 Backlight Problem
Update: tore down the panel and tested the strips. I found about 1/3 of the LEDs wouldnt light and one looked burned. i just ordered a set of replacement strips that will be here tomorrow so hopefully thats all i need. i will keep you all posted. thanks for the help so far!Leave a comment:
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Re: Insignia NS-55D420NA16 Backlight Problem
i guess next step is to take the screen apart and get to the actual strips. Thanks for the help so far guys. I will dig in tonight...Leave a comment:
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Re: Insignia NS-55D420NA16 Backlight Problem
What is the LCD panel model number?
http://www.shopjimmy.com/insignia-sv...55d420na16.htm
I am not sure if your LCD panel uses these LED strips or not, it has 66 LEDs.
Your tester show 130V which is kind of low, your tester is putting out around 20 ~ 30mA so the Vf for each LED will be about 2.7V instead of over 3V when driven at full current.
You may have some shorted out LEDs.Last edited by budm; 06-21-2018, 09:31 AM.Leave a comment:
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Re: Insignia NS-55D420NA16 Backlight Problem
It may be worth running it up again as you did above and in the menu turn the backlights down say to 50% and then reconnect the leds to the power board and see if the backlights stay on.
The led tester does not supply the same current to the leds as the power supply does so you may have a led breaking down at a higher current.Leave a comment:
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Re: Insignia NS-55D420NA16 Backlight Problem
So you connect the LED tester to the LED connector which is still connected to the power supply board and TV is also turned on?
What dose the LED tester meter show when you put the tester to the two wires of the LED connector without having it connected to the power supply board?Leave a comment:
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Re: Insignia NS-55D420NA16 Backlight Problem
Ok so I got my LED tester and plugged it into the led connector. I then powered the tv up and got a picture. I didn't notice any dim spots or areas of the screen so I don't think any of the leds are out. Would it be obvious if there were a problem with the leds themselves? I'm trying to avoid disassembling the screen if I can help it. Should I be replacing the power supply board now?Leave a comment:
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Re: Insignia NS-55D420NA16 Backlight Problem
Thats what im thinking. I have an LED tester coming today so i can check those out next.Leave a comment:
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Re: Insignia NS-55D420NA16 Backlight Problem
It is looking like a led or led strip connection problem.Leave a comment:
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TCL 75S421
PSU BOARD: 40-L402H8-PWD1CG
it shows not even a flash of backlight when powering up.
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unplug mb and leave only psu plugged into backlights (PSU + BL SELF TEST MODE?) does not light the backlights.
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with mb connected, PSON...
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