Insignia NS-LCD19 no picture but has back light and sound

[1simtime]

Re: Insignia NS-LCD19 no picture but has back light and sound

Timed out so I could not add to last post

Removed R67 short is gone at C1.
C34, C35 still 2.2 Ohms.

Q4 top leg to bottom left =15 Ohms
Q4Top to bottom right(goes to GND) =2.2 Ohms

Readings keep changing for all below
C20 .821M /280K Ohm
C23 314K Ohm
D3 - to anode , + to cathode = 172 Ohm
D3 + to anode , - to cathode = 119 Ohm
D2 - "........ " , + " ........." = 483K
D2 + "........ " , - " ........ " = 506K

[momaka]

Re: Insignia NS-LCD19 no picture but has back light and sound

Okay... so D2 and D3 are good.

Most likely Q4 is bad, but I think it would be easier if we start with C34 and C35 since they have 2 leads only - remove C34 and measure resistance either across C35 or across the pads where C34 was on the board.
- If 2.2 Ohm resistance is gone, check resistance on C34 out of circuit. A good ceramic capacitor will show infinite resistance out of circuit. If C34 doesn't, then it's bad.
- If 2.2 Ohm resistance is still there, remove C35, and repeat the same procedure you just did for C34. And if the 2.2 Ohm resistance is still there or if there is 2.2 Ohm resistance between top leg and bottom-right on Q4, then remove Q4 and measure resistance again across the various legs of Q4 out of circuit.

[1simtime]

Re: Insignia NS-LCD19 no picture but has back light and sound

Removed C34 good and C35 good.Still had 2.2 Ohms on board.
Removed Q4 (lower right leg where 2.2 ohm was came off) part was already heat damaged . Measured 27 Ohms on lower left.
2.2 ohms gone on board. So looks like Q4 is bad.

[1simtime]

Re: Insignia NS-LCD19 no picture but has back light and sound

If you think BCX70H will replace the NAH3, I found it at Digikey.
Here are the resistance readings for D1 I took before Q4 smoked.
looking at pic 3973 I used top left as pin 1 and went clockwise to 6
I used na for readings that changed .

+1 to -2=na........-3=na.......-4=na.....-5=na......-6=na
+2 to -1=.823M...-3=na.......-4=na.....-5=na......-6=na
+3 to -1=pulsed...-2=open....-4=na.....-5=na.....-6=na
+4 to -1=pulsed...-2=pulsed..-3=287K..-5=na.....-6=na
+5 to -1-.779M...-2=.590K....-3=472K..-4=285K..-6=na
+6 to -1=.285K...-2=515K.....-3=1.102K.-4=.985K..-5=na
.
D1 today with C34,C35 and Q4 removed
+1 to -2=277K......-3=.844M...-4=.724M...-5=.409K....-6=.798M
+2 to -1=.795M.....-3=521K....-4=411K.....-5=1.43K....-6=.477K
+3 to -1=pulse......-2=pulse....-4=open.....-5=open.....-6=open
+4 to -1=pulse......-2=pulse....-3=270K.....-5=pulse.....-6=pulse
+5 to -1=724M.....-2=pulse.....-3=269K.....-4=267K.....-6=456K
+6 to -1= 268K....-2=494K......-3=1.047M..-4=.859M....-5=536K
All the readings seem to change .That is why I did not post the 1st readings earlier.

[momaka]

Re: Insignia NS-LCD19 no picture but has back light and sound

Removed Q4 (lower right leg where 2.2 ohm was came off) part was already heat damaged . Measured 27 Ohms on lower left.
2.2 ohms gone on board. So looks like Q4 is bad.

Yes, unfortunately.

If you think BCX70H will replace the NAH3, I found it at Digikey.

I can't say for sure since I'm not that well versed with transistor replacements. If no one else posts an answer to this in a day or two, then feel free to open a new thread in the General Electronics forum. Just ask what would be a suitable replacement for the NAH3 transistor and put a link to this thread.

I have a few other ideas/solutions for the TV, but it's probably better to use them as last resort only since I can't be sure they will work, and they do involve a certain risk (as in, they may further damage the t-con if they don't work). So if you get to the point where you don't care about the TV and just want to try anything to get it working, I'll post them.

Meanwhile, you can reinstall R67, C34, and C35.

As for readings on D1, you need to use either 2000 Ohm scale or diode test function (assuming you have a manual-ranging digital multimeter). The reason for this is because diodes require a certain amount of current to conduct in the forward direction (red probe on anode, black probe on cathode). The diode test function is designed to supply this current, which is why it's usually a good idea to test diodes with it (note: on common digital multimeters, the diode test function is usually coupled with the continuity check). Also, on most digital multimeters, only the 2000 Ohm scale will be able to supply this forward-biasing current to test diodes. 200 Ohm scale can too, but diodes usually have a resistance in the 100 to 1000 Ohm range in the forward direction, so not all diodes will display a proper readings on 200 Ohm scale.

Now, I didn't see any short-circuits on D1, so it's probably okay. But if you want to retake the readings with either diode test function or 2000 Ohms, scale, I still wouldn't mind taking a look at the results.

[1simtime]

Re: Insignia NS-LCD19 no picture but has back light and sound

I have information on Q1 marked NAH3.
.
I will try to locate data sheets for D1 marked DNc

[momaka]

Re: Insignia NS-LCD19 no picture but has back light and sound

I have information on Q1 marked NAH3.
.

N-channel MOSFET - seems right for this application, as per the FP5138 datasheet.
Make sure to buy at least 3 of them (I'd say 5 is a good number), just in case. Or if you can't find this exact MOSFET, just find another one with similar characteristics. Tech support at Digikey or Mouser should be able to help with that.

[ButchPor]

Re: Insignia NS-LCD19 no picture but has back light and sound

I have looked over this thread and have the same problem, however, all of the TV and HDMI inputs work if the Monitor is cool (power off for a couple of hours), I can bring up the menu, the images are fine. However, once it warms up the screen goes blank but the back light and sound continues.
Any ideas that are more specific or should I follow this thread