Insignia NS-55E560A11 backlight turns off

[NUTIN2LUZ]

I have another TV repair that I have trouble for the past year. I bought this about 1.5 years ago broken and was searching online for a fix to the issue. The first owner said that it turned off on it's own. When I brought it home and plugged it in it worked for a few days. Then it would not turn back on and the front middle light kept blinking, no pattern just constant blink. After trying to find any cold solder joints on the power supply board, I tried again and it worked. Had it in storage for a year and decided to try and repair it. My kids was watching on it and my son told me he heard a small pop and the TV turned off and then came back on. The next day the backlight faded and only could hear the sound. I replaced the main board, but that was DOA and still waiting for a replacement. With the original main board there is a red LED light that blinks slow and then fast when the backlight goes out. I have a video to show on the blinks.

http://vidmg.photobucket.com/albums/...s/MVI_9105.mp4

I checked the voltages on XP802 on the power supply to the backlight inverter board on the 24V side I have 25.28V when backlight is on or off and sound is good. I have checked for cold solder joints on the power supply. I also checked all the caps on the power supply for any high ESR, but couldn't find any. What else should I be checking or should I just wait for the replacement main board come in and see if that fixes the problem?

[zacheriaj]

Re: Insignia NS-55E560A11 backlight turns off

are the backlights actually on when you get 25.3vdc? Seems like they wouldn't be especially if the reading doesn't change when you turn the tv off or on. Check F101 on the inverter board. If it is open, there might be a problem with the inverter board or you might be lucky and have it just be a fuse. What voltage readings do you get on XP805? List the voltages with the tv powered off and also powered on.

[budm]

Re: Insignia NS-55E560A11 backlight turns off

What DC Voltage do you have on the 'SW (BL_ON)' pin when TV is OFF and when TV is on? Same testing on the 'STB (PS_ON)' pin.
This is LED backlights TV with 4 LED strings.

[NUTIN2LUZ]

Re: Insignia NS-55E560A11 backlight turns off

Here are the readings I got:

XP805
-GND
-STB .029V (OFF), 3.68V (ON)
-5V_S 4.99V (OFF), 5V (ON)
-12V .016V (OFF), 11.84V (ON)
-12V .016V (OFF), 11.84V (ON)
-GND
-GND
-PMW 0V (OFF), 2.55V (ON)
-SW .011V (OFF), 4.67V (ON)
-GND
-GND
-18V 0V (OFF), 18.26V (ON)
-18V 0V (OFF), 18.26V (ON)

XP802
-10_4 0V (OFF), 2.55V (ON)
-10_3 0V (OFF), 4.77V (ON)
-10_2 .011V (OFF), 4.67V (ON)
-10_1 0V (OFF), .145V (ON)
-GND
-GND
-GND
-GND
-GND
-24V 0V (OFF), 25.28V (ON)
-24V 0V (OFF), 25.28V (ON)
-24V 0V (OFF), 25.28V (ON)
-24V 0V (OFF), 25.28V (ON)
-24V 0V (OFF), 25.28V (ON)

All of these readings is when the backlight is off and sound is present

[zacheriaj]

Re: Insignia NS-55E560A11 backlight turns off

Did you check F101? you can also measure the voltage on both ends of the fuse to see if it's open.

[budm]

Re: Insignia NS-55E560A11 backlight turns off

OK, the power supply is getting the correct command signals from the main board and it also puts out correct voltage to feed the LED driver board. So we need to look at the LED driver board next, so check the voltage on both ends of the fuse with ref to ground.

[zacheriaj]

Re: Insignia NS-55E560A11 backlight turns off

I think budm and I are on the same page

[NUTIN2LUZ]

Re: Insignia NS-55E560A11 backlight turns off

At the fuse I got 25.28V on both ends (F101 on LED driver board).

Don't know if this will help in any way.

CN201 on inverter board
-PIN 1 229.5V (BL_ON), voltage drops (BL_OFF)
-PIN 2 54.3V (BL_ON), voltage drops (BL_OFF)
-PIN 3 229.5V (BL_ON), voltage drops (BL_OFF)
-PIN 4 54.1V (BL_ON), voltage drops (BL_OFF)
-PIN 5 288.7V (BL_ON), voltage drops (BL_OFF)
-PIN 6 17.96V (BL_ON), voltage rises 18.17V (BL_OFF)
-PIN 7 288.8V (BL_ON), voltage drops (BL_OFF)
-PIN 8 110.4V (BL_ON), voltage drops (BL_OFF)

[budm]

Re: Insignia NS-55E560A11 backlight turns off

At the fuse I got 25.28V on both ends (F101 on LED driver board).

Don't know if this will help in any way.

CN201 on inverter board
-PIN 1 229.5V (BL_ON), voltage drops (BL_OFF)
-PIN 2 54.3V (BL_ON), voltage drops (BL_OFF)
-PIN 3 229.5V (BL_ON), voltage drops (BL_OFF)
-PIN 4 54.1V (BL_ON), voltage drops (BL_OFF)
-PIN 5 288.7V (BL_ON), voltage drops (BL_OFF)
-PIN 6 17.96V (BL_ON), voltage rises 18.17V (BL_OFF)
-PIN 7 288.8V (BL_ON), voltage drops (BL_OFF)
-PIN 8 110.4V (BL_ON), voltage drops (BL_OFF)

OK, the boosted Voltage circuits for driving the LED strings are working. The one with 288V reading may be indicating the string has open circuits due to bad LED which is very common failure mode for LED backlights TV.

[budm]

Re: Insignia NS-55E560A11 backlight turns off

Need closed up pictures.

[NUTIN2LUZ]

Re: Insignia NS-55E560A11 backlight turns off

Need closed up pictures.

Will post it late tonight.

[NUTIN2LUZ]

Re: Insignia NS-55E560A11 backlight turns off

Let me know if you need a better picture.