Insignia NS-L42Q-10A with no power/dead

[waitery]

I have an Insignia NS-L42Q-10A lcd that has no indication of power after being plugged in and the power button is pressed. No power LED or anything. Upon taking the back off the unit, I took a few measurements from the power board. I was getting no voltages on the rail, with the main board being plugged into the unit or not. No 5 volt stanby voltages either.

Fuse is good, check all the diodes and they are good as well. No burned/scorched components either. Caps are all Elite brand with the exception of the filter caps that are Rubycon. Checked the voltages on the big filter caps and both of them showed 5.90 volts on each of them while being plugged in. My thoughts are that I might have an issue with the SMPS controller IC, but I want to make sure that I am troubleshooting it the right way.

Board number is 715G3511-P02-000-003M and the pictures of the top and the bottom of the board are as follows:





Any thoughts, ideas on how to proceed would be more that welcome.

[budm]

Re: Insignia NS-L42Q-10A with no power/dead

Please redo the pictures by not posting them in line, please used GO ADVANCED and use the attachment function to up load the pictures. Thanks.
By the way, do you get any DC reading on those two large caps in the primary side?

[waitery]

Re: Insignia NS-L42Q-10A with no power/dead

Bud, I am not sure how to edit the original post, once it has been posted. Also, in my original post, you see that I have 5.90 volts on each of the large filter caps. Please let me know.

[tom66]

Re: Insignia NS-L42Q-10A with no power/dead

There is a fuse near the AC input, bottom left. With power disconnected, what does it measure on the 200 ohm range? If it is good, it should measure less than 1 ohm.

[waitery]

Re: Insignia NS-L42Q-10A with no power/dead

Hi Tom,

Yes, we're good on the fuse.....measured it out and we're looking at 1 ohm there, so no problems. My Fluke gives a ring for full continuity as well, so the fuse looks good here. Thanks!!

[tom66]

Re: Insignia NS-L42Q-10A with no power/dead

Okay, but you say you are only getting 6V across the caps?

Do you see the big green component next to the fuse? That is an NTC thermistor. Check it is not cracked or damaged in any way, and then ohm it out with your meter - should measure a few 10s of ohms cold.

PS: Fluke - I'm jealous!

[waitery]

Re: Insignia NS-L42Q-10A with no power/dead

OK, measured it out and it is 3.8 ohms. After visual inspection, I see no cracks, burns or anything else to lead me to believe that it is having an issue....it looks good to me, Tom.

The Fluke was a Father's Day present a few years back!

[tom66]

Re: Insignia NS-L42Q-10A with no power/dead

NTC is good. How are you checking the voltage across the big caps? Red on positive, black on negative?

When it was working, do you recall a sound of a relay clicking when the set is turned on or off?

[waitery]

Re: Insignia NS-L42Q-10A with no power/dead

Yeah, so when I have a load on the board, I measured both of those caps at 5.9 VDC, with red to positive and black to negative. Both filter caps were very low.

I actually got this set in the condition that it's in right now from someone, so I lack perspective here....not sure if a relay clicks or not.

[tom66]

Re: Insignia NS-L42Q-10A with no power/dead

Okay. I get a lot of TVs not knowing what they are supposed to do, so you have to make guesses. Case in point got an LCD TV with no sound or picture. Troubleshooted and fixed the picture problem, and found the user had simply muted the sound. I don't see a relay, so I'm guessing there isn't one.

It could be an open diode in the bridge rectifier. Diodes rarely fail open, but it is possible.

First let's do the "stupid" check - are you getting 115V AC out of the plug? Do you have fuses in your plugs in the US?

Then unplug the board from the set, rest it upside down on a flat non-conductive surface, and do the following checks (I assume you are competent around reasonably high voltages - be careful.)

[waitery]

Re: Insignia NS-L42Q-10A with no power/dead

No problem at all. Yes, bridge works great. AC side is 122.4 VAC and the DC side is 168.2VDC. We are looking good there.

[tom66]

Re: Insignia NS-L42Q-10A with no power/dead

Okay, this is getting odd. I'm thinking a cold joint is more likely now. Let's see if there's a way for the bridge power to get to the capacitors. One way may be open causing the low voltage on the caps. Follow the instructions in the image. Do these checks with the board power unplugged.

[waitery]

Re: Insignia NS-L42Q-10A with no power/dead

Sorry, I misunderstood you. So I do have continuity between both those point and the filter caps. No problem there.

[tom66]

Re: Insignia NS-L42Q-10A with no power/dead

Your last check was good, and it shows the bridge is working. Now I'm trying to see if there is a broken connection between the bridge and capacitors.

[waitery]

Re: Insignia NS-L42Q-10A with no power/dead

Thanks Tom, I have been looking under a scope for problems and I can't seem to find anything under visual inspection.

[selldoor]

Re: Insignia NS-L42Q-10A with no power/dead

Is that grey resistor between the heatsinks a fusible resistor. Pics could have been a bit clearer.

[tom66]

Re: Insignia NS-L42Q-10A with no power/dead

I'm thinking it's possible one of the yellow inductors is open circuit. They run hot. If this is the case, the fix would be to replace the power supply, as those components are custom.

[waitery]

Re: Insignia NS-L42Q-10A with no power/dead

The grey resistor is fuseable and it is fine. I just checked it.

[selldoor]

Re: Insignia NS-L42Q-10A with no power/dead

Can you mark on a picture where the cap legs are soldered through - my front back geography is hopeless and your pictures I think are not in the same plane.

[waitery]

Re: Insignia NS-L42Q-10A with no power/dead

Your asking for the filter capacitor legs, correct?