Insignia NS-LTDVD20

[JadeMattican]

When the screen is first powered on, it shows a picture for about a second and goes out. There is still sound, and if you shine a light on it, you can see the image... I decided to treat this like a 2 seconds to black issue, despite the fact that it's definitely shorter than 2 seconds... That said, I started with the power supply...

The P/S P/N is DTV207.
My opinion is that the p/s is shot. (See Attached Pics.)

First, there is a chip on the bottom of the board that looks kinda melty to me. There is also, solder bridging a total of 5 of the 8 pins on the same chip. In addition, I think some of the other solder joints show poor workmanship.

On the top side of the board, there are 2 heat sinks... One of which shocked me. (Power was connected because I was testing the output voltages.) As far as I know, a heat sink shouldn't be able to shock anything. After my shocking experience, I tested the voltage coming off of the heatsink, and it's putting out 77 VDC. In addition to that, the ground screw was the hot side and the heat sink was the ground. (according to my digital multimeter. See Pic.) The heat sink that shocked me has only 1 transistor attached to it. the other heat sink has 2, but didn't shock me & wasn't putting out any voltage.

Questions? Comments? Please feel free... If anything here is normal and I'm overreacting, please let me know...

[retiredcaps]

Re: Insignia NS-LTDVD20

First, there is a chip on the bottom of the board that looks kinda melty to me. There is also, solder bridging a total of 5 of the 8 pins on the same chip. In addition, I think some of the other solder joints show poor workmanship.

The 4835p chips definitely look like they are burnt. I have seen this first hand on a board when I smelled smoke. I quickly disconnected the power and the burnt IC (not 4835p, but similar) looks like the pictures.

The datasheet for the 4835p is here.

http://pdf1.alldatasheet.com/datashe...F4835PSLA.html

1,2,3 = are all source, 4 = ground, 5,6,7,8 = drain. So it is possible that some of these pins are intentionally bridged despite the poor solder job.

After my shocking experience, I tested the voltage coming off of the heatsink, and it's putting out 77 VDC.

On your multimeter pics, I usually have black to GND (screw) and red to the test point. Yours is reverse.

[Tvbob]

Re: Insignia NS-LTDVD20

You have two grounds in you set, hot ground and cold ground.
Hot ground feeds back thru the ac bridge rectifiers to the hot (black) side of the ac line.
It is common place to get shocked there. It looks like your burnt ic is the (electronic switch) that supplies 24 volts to the backlight inverter board,check the inverter board for shorts, Google the chip and you should be good to go.( if you don't find any shorts on the inverter board you can jumper a 2A pico fuse across the chip to get your 24 volts to the inverter board) there should be a couple of electrolytic caps there also. good luck.

[PlainBill]

Re: Insignia NS-LTDVD20

1. Live points on the power supply - normal. 77 Volts to ground - also normal. Getting a shock while making voltage measurements - annoying, and educational.

2. Q04 looks unusual. It's an AnaChip AF4835PS. It is PROBABLY not the cause of your problem. Many power supplies have the output connectors labeled. Verify the output voltages, also verify the input voltage to the inverter, as well as the BL_ON signal into the inverter.

3. 'Two seconds to black' is a convenient label. I had it manifest itself as a 1/2 second to black. A common cause is a bad transformer on the Darfon inverter popular with many LCD TVs.

4. No sign of bad caps on the power supply. That's not definitive, but look to the inverter first.

5. You perhaps went overboard on the pictures, but it is MUCH better to have them to look at than to rely on descriptions. That also applies when dealing with the inverter.

PlainBill

[kc8adu]

Re: Insignia NS-LTDVD20

the mosfet in those first 2 pics is toast.

[JadeMattican]

Re: Insignia NS-LTDVD20

Attached are 2 pics of what I'm assuming is the inverter board for the backlights and another pic of the power board where the output voltage is.

I've checked the voltage and it appears to be putting out what it's supposed to.

As to the B-On pin... Should I be testing it to a ground? What kind of reading should I be getting there?

I've been messing around with the backlight inverter board with my digital multimeter... Correct me if it's not a transformer of some sort. (See the first 2 pics.) Each transformer has 6 contacts across the top and 4 across the bottom. Do these readings look right? They look ok to me, but that's why I'm here... I'm learning!

Bottom Row Left Side
Pins 1 & 2 =0.3k ohms
Pins 1 & 3 =0.462k ohms
Pins 1 & 4 =0.462k ohms
Pins 3 & 4 =0.3k ohms

Bottom Row Right Side
Pins 1 & 2 =0.3k ohms
Pins 1 & 3 =0.459k ohms
Pins 1 & 4 =0.459k ohms
Pins 3 & 4 =0.3k ohms

Top Row Left Side All Pins
1.1 Ohms

Top Row Right Side All Pins
1.1-1.4 Ohms

[PlainBill]

Re: Insignia NS-LTDVD20

Attached are 2 pics of what I'm assuming is the inverter board for the backlights and another pic of the power board where the output voltage is.

I've checked the voltage and it appears to be putting out what it's supposed to.

As to the B-On pin... Should I be testing it to a ground? What kind of reading should I be getting there?

I've been messing around with the backlight inverter board with my digital multimeter... Correct me if it's not a transformer of some sort. (See the first 2 pics.) Each transformer has 6 contacts across the top and 4 across the bottom. Do these readings look right? They look ok to me, but that's why I'm here... I'm learning!

Bottom Row Left Side
Pins 1 & 2 =0.3k ohms
Pins 1 & 3 =0.462k ohms
Pins 1 & 4 =0.462k ohms
Pins 3 & 4 =0.3k ohms

Bottom Row Right Side
Pins 1 & 2 =0.3k ohms
Pins 1 & 3 =0.459k ohms
Pins 1 & 4 =0.459k ohms
Pins 3 & 4 =0.3k ohms

Top Row Left Side All Pins
1.1 Ohms

Top Row Right Side All Pins
1.1-1.4 Ohms

Good work. The transformer windings on the dual inverter design have a much lower resistance than the more common single inverter design.

Yes, check the backlight control signal to ground. I would expect about 3 - 5 volts if the backlights are turned on, less than .5 volts if they are turned off. If the control signal is 'on', but the backlights are 'off', that indicates a problem with the inverter. These inverters are known to have a high failure rate.

PlainBill

[JadeMattican]

Re: Insignia NS-LTDVD20

B-on shows 5.6 V DC when the tv is turned on, but the backlights only flicker on for about a second or so.

B-on shows 6.1mv DC when the screen is off...

So... Bad backlight inverter board? Could it be the caps on the inverter board are bad? They are TF brand 25V 330uf.

[dansciol]

Re: Insignia NS-LTDVD20

What was the fix on this problem?
Thanks