Dead Insignia 42" NS-L42Q-10A

[Spork Schivago]

Hi. My sister gave me this Insignia 42" NS-L42Q-10A flat screen. At first, I thought it'd be an easy fix. It doesn't power on at all. I looked an the main board, and capacitor C743 was blown. I replaced it but still nothing. I have attached some pictures and the service manual. On the power board, there's a connector that goes to the main board. It's CN903. I've tested the voltages with the TV off and turned on. This is what they read:

CN903 ON OFF
ON/OFF 0.5mv 0.5mv
PDIM -0.2mv -0.2mv
+12V 14mv 18.6mv
+12V 14.1mv 17.8mv
Gnd
Gnd
Gnd
24V 12.1mv 11.4mv
24V 12.1mv 11.5mv
PS_ON 125.3mv 125.4mv
5V 5V 5V
5V 5V 5V

I also tried doing some tests on what I think are the voltage regulators. With the TV turned off, I tested the resistance between pin 3 and ground and then the long tab at the top of the voltage regulators and ground. This is what I get:

Pin 3 - Gnd Long Tab - Gnd
U709 654 ohm 1.236Kohm
U708 4.6Mohm 0.654Kohm
U703 1.65Kohm 153.1ohm
U702 0.4ohm 0.3ohm

U708 on pin 3 just kept climbing. Also, U703 on pin 3 kept on climbing too. I just didn't hold it there for very long. Shouldn't U702 be reading higher? Does this mean there's a short some wheres? And is U708 so high because it's bad?

Also, I pulled off this little cover and was looking at some of the stuff under it and it looks like some of the surface mount stuff might of leaked. C401 and C451.

My sister, when she gave it to me, she said it had a blue line going all the way down the middle of the screen and someone told her it was dead pixels. Didn't really make sense to me why dead pixels would die in a straight line and be blue but I guess my sister says the guy claims to be a professional with these TVs. I was thinking maybe those two caps, C401 and C451 might of caused the blue line?

She also said she had the XBOX 360 hooked up to the TV via HDMI and all of the sudden the TV just shut off and the 360 started making a weird buzzing noise. She took the 360 back to the store, they tested it and said it was shot and they replaced it for her. It wasn't storming out or any thing and nothing else was effected. I believe the 360 and TV where on surge protectors. Could anyone please help me figure out how to fix this TV? I'd greatly appreciate it.

[Spork Schivago]

Re: Dead Insignia 42" NS-L42Q-10A

So I was wondering if I could replace the U702 voltage regulator with this other one I found on another board. The U702 has this printed on it:
1084
-18PE
185E8R

The other one has this printed on it:
AMS1117
1.8 0137

It's a little bit smaller but I think the pins will match up with the pads. Do you guys think this would work?

[Spork Schivago]

Re: Dead Insignia 42" NS-L42Q-10A

I took my multimeter and read the voltages coming off the AO4449 P-Channel Enhancement Mode Field Effect Transistor (Q703). It's an 8 pin chip. I'm not 100% sure on how to test these. The Source and Drain's all read 5.00VDC but the gate was jumping all around. I tested it with the power plugged into the TV and I hit the on button. The Source is at 5.00v, the Gate is at 4.46v (but some times it jumps around a bit, I don't know if it's me not getting a good connection with my probe or not), and the Drain is at around 0.7mv. Does anyone know how to test a P-Channel Enhancement Mode Field Effect Transistor? I tried googling it and I found some stuff on N-Channel types but nothing on the P-Channel type. Any suggestions?

[budm]

Re: Dead Insignia 42" NS-L42Q-10A

If you remove U702 off the board and then test the resistance on those empty pads against GND, what do you get?
BTW, LM1084 series is bigger because it is rated at 5A in stead of 1A for 1117 series.

[Spork Schivago]

Re: Dead Insignia 42" NS-L42Q-10A

So would replacing LM1084 with 1117 cause problems? I tried removing U702 and I got it off, but in the process I damaged it pretty bad. It broked in half. I will remove the 1117 that I put on and check the resistance. I believe earlier, when I checked, they both read 0 ohm. But I'll double check that. If it does read 0 ohm resistance for both pads, that means there's a short some wheres, right?

[budm]

Re: Dead Insignia 42" NS-L42Q-10A

1117 will not handle 5A.
Without U702 in place and the Input pin pad and the output pin pad show <1 Ohm then you do have shorts circuit at least two places.

[Spork Schivago]

Re: Dead Insignia 42" NS-L42Q-10A

I just removed 1117 and yeah, on all three empty pads, I get 000.0 ohm resistance when checking against GND. If I wait a couple seconds and check again, it's at 000.4 or so on both the small pads.

[Spork Schivago]

Re: Dead Insignia 42" NS-L42Q-10A

Okay, do you have any suggestions on how to track down a short like that? Could it be a faulty capacitor? I think maybe it's a design flaw. I was reading another forum where the guy had an Hitachi board. It looks almost identical to mine minus U702 being in a different spot. He has the same problem with there being a short some wheres.

[budm]

Re: Dead Insignia 42" NS-L42Q-10A

But you install 1117 in place of 1084? All we want to know right now is do you get low resistance on the input pin and GND, and low resistance on the output pin and GND WITHOUT the IC in place.

[Spork Schivago]

Re: Dead Insignia 42" NS-L42Q-10A

I didn't mean a dead capacitor, I meant a dead diode. Sorry, it's been a long day.

[Spork Schivago]

Re: Dead Insignia 42" NS-L42Q-10A

yes, I had installed 1117 earlier today and removed it before I did the test you asked me to do. There was no voltage regulator there when I did the test. For all three pads, I get 000.0 Ohm at first. If I wait a few seconds and test them again, it reads around 000.4 ohm.

[budm]

Re: Dead Insignia 42" NS-L42Q-10A

Okay, do you have any suggestions on how to track down a short like that? Could it be a faulty capacitor? I think maybe it's a design flaw. I was reading another forum where the guy had an Hitachi board. It looks almost identical to mine minus U702 being in a different spot. He has the same problem with there being a short some wheres.

This one?
https://www.badcaps.net/forum/showth...446#post506446
Not easy to locate shorts since the connections will spread all over the places and without the diagram it will be real difficult.
It can be as simple as shorted out MLCC (Multi Layer Ceramic Capacitor) which they do failed as short circuit.

[Spork Schivago]

Re: Dead Insignia 42" NS-L42Q-10A

yes, that's the one. I do have the service manual for this Insignia. I'm just not very good at reading the schematics that are in it.

[Spork Schivago]

Re: Dead Insignia 42" NS-L42Q-10A

I also have an Oscilloscope. I haven't really learned how to use it yet though. Could that help me track it down?

[Spork Schivago]

Re: Dead Insignia 42" NS-L42Q-10A

Hey Budm, do you think the problem could be around C743? That's where the cap was blown. Also, if I flip the board over, there's this rectangle silver part of the board, I think a ground plane or something like that. It looks like it had some solder on it or something, but part of it is bubbly. Part of it is real flat and then the other part is bubbly and there's like a small whole in part of what I think is solder. It's by the tuner and right by that blown capacitor I replaced, C743.

Also, on the top side, same area, there's two voltage regulators. One of them though, U708, for pin 3, when I check against ground, it's reading around 12.13 mohm. Other times, it reads OL. Could the short be around this area? Thanks for the help and I'm sorry I'm not very knowledgeable in this stuff. I do love learning though and every time I try fixing a broken TV, I do pick up stuff and improve. Thanks again for the help.

[budm]

Re: Dead Insignia 42" NS-L42Q-10A

"U708, for pin 3, when I check against ground, it's reading around 12.13 mohm. Other times, it reads OL" Do you mean 12.13 Million Ohms?
If you suspect the cap is bad, then remove it to see if the shorts goes away, it will be process of eliminating which without diagram it will be just impossible because you will no way to find out how many components are connected to the same connections that showing < 1 Ohm.
Just type in this into your search engine ""how to find shorted circuit on PCB"

[Spork Schivago]

Re: Dead Insignia 42" NS-L42Q-10A

Okay, thank you. Yes, 12.13 Million Ohms. I thought they where called Mega Ohms. When you say diagram, do you mean schematic? Because the schematics are in the service manual I attached in my first post. Is that not what we need? It also has the PCB layout (starting on page 59). The schematics for the main board is roughly on page 81 I believe. I will google what you typed. Thanks for the info.

[budm]

Re: Dead Insignia 42" NS-L42Q-10A

Mega is the same as Million.
That Schematic is exact match to your board?

[budm]

Re: Dead Insignia 42" NS-L42Q-10A

OK, let me get this correctly, looking at the pads of the U702 with big tab up, the center pin (same as big tab) which is the output pin is showing <1 Ohms between this pin and Ground, also the between the right pin (output pin) and Ground also shows <1 Ohm?
That will be real strange to have both input and output showing <1 Ohm.
Per diagram, the output pin of U702 named 1V8_STB, so you will have to at all the SCH pages to see where it is connected to, so far I see:
IC U505 page 72
U401Q page 75

The input pin of U702 is fed by 3V3_STB (page 81) which is generated by U706 3.3V Buck regulator that converted the +5VSB into 3.3V.
If you look at page 69, the 3.3V_STB is generated either by U702 Buck regulator or U701 3.3V fixed regulator, I do not know which one you have on your board.
So it is very important that you read those resistance correctly and verify U701, 706.

[Spork Schivago]

Re: Dead Insignia 42" NS-L42Q-10A

Sorry for the delay Budm, I was researching what you asked me to with finding the shorts. I found two ways essentially, one involves a benchtop PSU, which I don't have. The other one I'm a little confused on, but have the basic idea.

To answer your question, yes, I believe that service manual is for my exact TV board. However, it also has schematics for the 37", which I believe is a different board. My main board is the 715G3269-1. In the manual, they seem to refer to it as the 715T3269-1 (page 81).

For the pads where U702 was, all three pads, the left pad (pin 1), the right pad (pin 3) and the fat tab all read 000.0 ohm. If I leave the multimeter there for a bit, it'll go up to about 0.4 ohm. I have the board removed from the TV.

I can't seem to find U701. U706 is a ten pin chip. Just so I'm sure, you want me to test every connection on that ten pin chip against ground and give you the resistance?