Insignia ns32d201na14 - TV works, no backlight

[smalltownguy]

Picked up an Insignia ns32d201na14 for free at a yard sale. Plugging in the TV, the standby light comes on red and stays red. Pushing the power button, the standby light begins to flash slowly red for 5-6 blinks, then goes out. At that point, the TV is on, because when I push the "menu" button, I can see the menu options on the screen if I shine a flashlight on it.

So the LED's are not lighting.

I took the back off the TV, and metered the connector for the LED's for voltage. I got nothing for DC voltage. OK, so it's a power supply problem. Check the caps, right?

I pulled out my ESR meter and checked all the caps on the power supply board - none of them are bulging, and they are all in an acceptable range on my ESR meter.

What next?

Pics attached.

[budm]

Re: Insignia ns32d201na14 - TV works, no backlight

Pictures of the whole back side of the TV so we can see how all the boards are connected together.
What DCV do you have between the two legs of C520?
What DCV do you have between the LED connector L+ and gnd?

[smalltownguy]

Re: Insignia ns32d201na14 - TV works, no backlight

No problem. Attached. Got some pics of the main board too.

[budm]

Re: Insignia ns32d201na14 - TV works, no backlight

Holy crap, looks like Westinghouse TV.
Please check the dcv as requested.

[smalltownguy]

Re: Insignia ns32d201na14 - TV works, no backlight

Pictures of the whole back side of the TV so we can see how all the boards are connected together.
What DCV do you have between the two legs of C520?
What DCV do you have between the LED connector L+ and gnd?

What DCV do you have between the two legs of C520? 64.7v - 67.5v

What DCV do you have between the LED connector L+ and gnd? 79.9v - 85.1v

[budm]

Re: Insignia ns32d201na14 - TV works, no backlight

OK, what is the dcv rating as printed on the body of C618?
So far it looks like you have open circuit in the LED string.
Check the DCV between L- in GND.

[smalltownguy]

Re: Insignia ns32d201na14 - TV works, no backlight

OK, what is the dcv rating as printed on the body of C618?
So far it looks like you have open circuit in the LED string.
Check the DCV between L- in GND.

C618 is a 68uf 100v cap.

I don't understand your 2nd request.... did you mean check DCV between L- AND ground? If so, where do I find L-?

EDIT: Wait, did you mean measure the DCV between LED2- and ground? That measurement floats between 35vdc and 29vdc.

[budm]

Re: Insignia ns32d201na14 - TV works, no backlight

Sorry about that, it is LED2-.
OK, remove the LED connector and check LED2- and GND again.
BTW, 85V feeding the Anode pin of the LED string is correct.

[smalltownguy]

Re: Insignia ns32d201na14 - TV works, no backlight

Sorry about that, it is LED2-.
OK, remove the LED connector and check LED2- and GND again.
BTW, 85V feeding the Anode pin of the LED string is correct.

Thanks for the info.

Removing the LED connector, I get 1.5vdc on the LED2- and ground.

[budm]

Re: Insignia ns32d201na14 - TV works, no backlight

OK, the LED string does not have open circuit then otherwise it will not show 35V or so on the LED2- (Cathode return pin of the LED string), but it looks like the PWM controlled MOSFET V602 is not turned on, so we need to check the DCV on the PWM pin and the BON pin of the connector X503.
Please show us what you have on those 2 pins.

[smalltownguy]

Re: Insignia ns32d201na14 - TV works, no backlight

BON pin is 5vdc.

PWM is 2.47vdc.

[budm]

Re: Insignia ns32d201na14 - TV works, no backlight

OK, we need to find out next if the Gate of V602 is getting the drive Voltage, so check the DCV between Gate and Source pins.
This is where LED tester comes in handy, you can try bypassing the PWM controlled MOSFET with resistor but we do not know how many LEDs are in the string to properly calculate the value of the resistor to limit the current otherwise you can damage the LEDs.
It may have some shorted out LEDs so the circuit goes into shut down by not turning on the PWM MOSFET.
Looking at the Voltage readings
85V feeding the string, 35V on the MOSFET, so the Vdrops on the LED string is 85V-35V = 50V
50V/3V about 16 LEDs but we do not know for sure, I would expect more than 16 LEDs for 32" TV.

[smalltownguy]

Re: Insignia ns32d201na14 - TV works, no backlight

OK, we need to find out next if the Gate of V602 is getting the drive Voltage, so check the DCV between Gate and Source pins.
This is where LED tester comes in handy, you can try bypassing the PWM controlled MOSFET with resistor but we do not know how many LEDs are in the string to properly calculate the value of the resistor to limit the current otherwise you can damage the LEDs.
It may have some shorted out LEDs so the circuit goes into shut down by not turning on the PWM MOSFET.
Looking at the Voltage readings
85V feeding the string, 35V on the MOSFET, so the Vdrops on the LED string is 85V-35V = 50V
50V/3V about 16 LEDs but we do not know for sure, I would expect more than 16 LEDs for 32" TV.

I don't see V602. I DO see V501 - did you mean that one?

voltage across gate and source pins of V501 is about .85 volts.

[smalltownguy]

Re: Insignia ns32d201na14 - TV works, no backlight

Bump. Anyone?

[smalltownguy]

Re: Insignia ns32d201na14 - TV works, no backlight

Bump. Looking for any more advice.

[budm]

Re: Insignia ns32d201na14 - TV works, no backlight

https://www.badcaps.net/forum/attach...3&d=1466702535
V602 by the bottom edge of the board.

[smalltownguy]

Re: Insignia ns32d201na14 - TV works, no backlight

https://www.badcaps.net/forum/attach...3&d=1466702535
V602 by the bottom edge of the board.

Okay, assuming pins 1 and 3 are the gate and source pins (with the middle pin being the drain), I get no measurable voltage across those two pins. I observed the voltage while turning the TV on and off, and I never observed anything more than a few milli-volts. So I'm assuming that means no voltage at that mosfet.

Next?

[smalltownguy]

Re: Insignia ns32d201na14 - TV works, no backlight

Also, reading this thread here:

https://www.badcaps.net/forum/showth...t=54043&page=2

That 32" panel had 18 LED's in it, so that would make sense - 50v / 3v each gives me just under 17 LED's, so 18 could be the number.

[smalltownguy]

Re: Insignia ns32d201na14 - TV works, no backlight

Bump.

[dick_barton]

Re: Insignia ns32d201na14 - TV works, no backlight

Have you checked D602 and V603 which looks as though they may have heated up the bottom of the board.