Insignia NS-55D420NA16 Backlight Problem

[Stu71584]

Hi All,
Did a little bit of searching but i couldnt find anyone with a model that looks like mine so figured i'd make a post to try to get some help troubleshooting. We have an Insignia (hisense) 55" LED with a backlight problem. when i turn the TV on the backlights come on for about a second but then immediately shut off. once the backlights are off the panel is still working and i have sound but no backlights. I opened up the TV this weekend and tested the output from the power supply board. I get voltage coming out for the second the backlights are on but then nothing once they shut off. im suspecting something with the power supply but not really sure how to validate this.

I didnt take pictures of everything but i do have pictures of the power supply board. There was also a t-con board and main board inside this tv.

Open to any suggestions on what i can test to try to get this back up and running.

Thanks!

Peter

[Stu71584]

Re: Insignia NS-55D420NA16 Backlight Problem

as an update, the inside of the TV looks very similar to this one i found on youtube.

[dick_barton]

Re: Insignia NS-55D420NA16 Backlight Problem

Can you list the voltages against the pin names in the red box.
What voltage do you have on the connector in the green box when you power up.

[Stu71584]

Re: Insignia NS-55D420NA16 Backlight Problem

Hi,

See below for the voltages on the 10 pin connector:

Gnd: 0v
Gnd: 0v
Pwm12: 4.8v
Sw: 2.8v
12v: 11.9v
12v: 11.9v
Stb: 3.3v
Gnd: 0v
16v: 18.9v
16v: 18.9v

For the led connector it peaks at 56 volts for the half a second the backlight turns on then drops to .9 volts.

Also I took a video of the backlight turning on and it appears only one side is working. Would that indicate bad LEDs??

https://youtu.be/84RGStWo4bM

[dick_barton]

Re: Insignia NS-55D420NA16 Backlight Problem

There looks like at least 15 pins on the connector but you have only listed 10 of them.

Does your multimeter have min/max function to check the led voltage which spikes to a maximum and then drops quickly. According to the print on the circuit board it should be around 200V to drive the leds.

[budm]

Re: Insignia NS-55D420NA16 Backlight Problem

Hi,

See below for the voltages on the 10 pin connector:

Gnd: 0v
Gnd: 0v
Pwm12: 4.8v
Sw: 2.8v
12v: 11.9v
12v: 11.9v
Stb: 3.3v
Gnd: 0v
16v: 18.9v
16v: 18.9v

For the led connector it peaks at 56 volts for the half a second the backlight turns on then drops to .9 volts.

Also I took a video of the backlight turning on and it appears only one side is working. Would that indicate bad LEDs??

https://youtu.be/84RGStWo4bM

Is the reading on the LED connector with ref to chassis GND?

[Stu71584]

Re: Insignia NS-55D420NA16 Backlight Problem

There looks like at least 15 pins on the connector but you have only listed 10 of them.

Does your multimeter have min/max function to check the led voltage which spikes to a maximum and then drops quickly. According to the print on the circuit board it should be around 200V to drive the leds.

there are labels for more than 10 pins but the connector only has 10 pins and the plug only has 10 wires. the voltages are listed from left to right from the plug side.

i retested again and the output to the LEDs hits like 190ish volts for a split second when the backlights come on.

Thanks!

[Stu71584]

Re: Insignia NS-55D420NA16 Backlight Problem

Is the reading on the LED connector with ref to chassis GND?

yes. the 56v was to chassis ground. my meter doesnt have min/max so i may not be getting an acurate reading since the voltage spikes and drops so quickly.

i retested again using the connector ground and it spikes at around 190 volts.

[budm]

Re: Insignia NS-55D420NA16 Backlight Problem

yes. the 56v was to chassis ground. my meter doesnt have min/max so i may not be getting an acurate reading since the voltage spikes and drops so quickly.

i retested again using the connector ground and it spikes at around 190 volts.

OK, there are two wires for the LED connector.
Red wire is the Anode pin of the LED strip
White wire is the Cathode return of the LED strip.
So you are getting about 190V on the red wire and 0V on the wire?

[Stu71584]

Re: Insignia NS-55D420NA16 Backlight Problem

OK, there are two wires for the LED connector.
Red wire is the Anode pin of the LED strip
White wire is the Cathode return of the LED strip.
So you are getting about 190V on the red wire and 0V on the wire?

The 190v reading was across the two pins of the connector. red to red and white to black on my meter.

I also ordered an LED tester to check the backlights as some of my research is leading me to believe they might be bad.

[dick_barton]

Re: Insignia NS-55D420NA16 Backlight Problem

It is looking like a led or led strip connection problem.

[Stu71584]

Re: Insignia NS-55D420NA16 Backlight Problem

Thats what im thinking. I have an LED tester coming today so i can check those out next.

[Stu71584]

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?

[budm]

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?

[Stu71584]

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?

I connected the tester to the two wires of the led connector without it being connected to the power supply board. The led tester showed 130 volts. I was able to turn the tv on and It showed a picture like this.

[dick_barton]

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.

[budm]

Re: Insignia NS-55D420NA16 Backlight Problem

I connected the tester to the two wires of the led connector without it being connected to the power supply board. The led tester showed 130 volts. I was able to turn the tv on and It showed a picture like this.

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.

[Stu71584]

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...

[Stu71584]

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!

[Andrew F. Ali]

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!

From what I have read so far, the new strips should get you TV up and running again.