Dell inspiron N7110 LCD no back light

[bigsam731]

Hello all. I'm new to the community and my apologies if this was discussed in a previous post. I have a Inspiron 17R N7110 that has dim backlight to the LCD. When I plug it it to an external monitor i can see everything in that monitor. I searched every where for a solution but nothing on my model, all I find is solutions for the 1545 model which tells me to replace the F1 or F8 fuse. If that's the case on mine, does anyone know where are those fuses located? thanks in advance

My motherboard model is
DA0R03MB6E0 REV; E

[diif]

Re: Dell inspiron N7110 LCD no back light

Around where the video cable connects to the motherboard.

[bigsam731]

Re: Dell inspiron N7110 LCD no back light

I tested all the caps and resistors around the LCD cable they were all good. Is there a switch that control the back light to the LCD?

[bigsam731]

Re: Dell inspiron N7110 LCD no back light

here is the closest datasheet that I can find for my motherboard. If anyone can figure something out that would be very helpful.
https://drive.google.com/file/d/0B4e...k2b2swR2s/view

[diif]

Re: Dell inspiron N7110 LCD no back light

Decent close up photos of the motherboard would help.
Some Dells have a lid switch that can have an effect on the screen.

[bigsam731]

Re: Dell inspiron N7110 LCD no back light

https://drive.google.com/open?id=0B4...lvV0dmMnUwVmI0
https://drive.google.com/open?id=0B4...QydUFXQXp2emhJ
https://drive.google.com/open?id=0B4...M4b2JFNjFabjlF
https://drive.google.com/open?id=0B4...p4dE44TEtCaGxj
https://drive.google.com/open?id=0B4...lWalhwZW9qWWs4
https://drive.google.com/open?id=0B4...lnMGl5N3M5NE53

[meritosari]

Re: Dell inspiron N7110 LCD no back light

Around where the video cable connects to the motherboard.

I think the video cable connects to J2 ( IMG_0025) near hole and RB's mark.

@bigsam731

To check circuits was work or not, make sure you've connecting flex cable to mobo.

- measure on pins 38 39 40 of J2 connector (P.18 on schematic) should be +19V
- on pin 2 & 3 of J2 should be + 3.3V, This point usually have problem, if you get no voltage in here, trace back to signal LCDVCC_TST EN, sometimes bad mosfet or missing signal en for Q2 ( more complicated, could be chipset was bad, hope not)
- on Q23 at gate should be high to transfer +3.3V_RUN to be +LCDVCC

sorry for bad english

[diif]

Re: Dell inspiron N7110 LCD no back light

They aren't good enough quality to identify components on the board.
See if you can find a small surface mount device possibly coloured and possibly with a letter(s) on it.

[bigsam731]

Re: Dell inspiron N7110 LCD no back light

I think the video cable connects to J2 ( IMG_0025) near hole and RB's mark.

@bigsam731

To check circuits was work or not, make sure you've connecting flex cable to mobo.

- measure on pins 38 39 40 of J2 connector (P.18 on schematic) should be +19V
- on pin 2 & 3 of J2 should be + 3.3V, This point usually have problem, if you get no voltage in here, trace back to signal LCDVCC_TST EN, sometimes bad mosfet or missing signal en for Q2 ( more complicated, could be chipset was bad, hope not)
- on Q23 at gate should be high to transfer +3.3V_RUN to be +LCDVCC

sorry for bad english

Don't worry about it your english is fine. I did measure pins 39, 39, 40 and I got 19V on all of them. I also got 3.3V on pins 2 and 3. The only conflict I got,accourdinf to the schematics, was on pin 36. It suppose to be 3.3V where I get 19V. I'm going to try to de-solder pin 36 wire from the cable and give it 3.3V to see if I can get some light to the LCD. If that works, then I think IT8518 defective because there's nothing between pin 36 on J2 and pin 18 on IT8518 besides R472 resistor, which I already tested it and it was fine. I might be wrong too.

Oh BTW, I did the testing on both sides of the LCD cable and i got the same reading.

[bigsam731]

Re: Dell inspiron N7110 LCD no back light

They aren't good enough quality to identify components on the board.
See if you can find a small surface mount device possibly coloured and possibly with a letter(s) on it.

I can get you closer photos if you tell me which sections you like to see.

[meritosari]

Re: Dell inspiron N7110 LCD no back light

Don't test for long time, it's seem complicated more than I thought, really. The ITE chips can not handle high voltage ( on laptop 19v it is the higher), should be the higher is 3.3V for EC/KBC chips. Need more carefully investigate what cause 19V on pin 36. Does the pin 36 join to pin 38?

[bigsam731]

Re: Dell inspiron N7110 LCD no back light

So this what I did for a test, I attached pin 36 on the LCD cable to pin 2. And sure enough, I NOW have back light on the LCD. I know its a bad soldering job but I figured it was just a test. Here are some pics...

https://drive.google.com/open?id=0B4...JWUkc0b082cnhB
https://drive.google.com/open?id=0B4...BWRVZNbHB0S05B

[bigsam731]

Re: Dell inspiron N7110 LCD no back light

Don't test for long time, it's seem complicated more than I thought, really. The ITE chips can not handle high voltage ( on laptop 19v it is the higher), should be the higher is 3.3V for EC/KBC chips. Need more carefully investigate what cause 19V on pin 36. Does the pin 36 join to pin 38?

I really don't know what is the cause 19V on pin 36. I know that it's not connected to pin 38. the only thing that I can see between pin 36 on IT8518 is the R472 resistor which i de-soldered and tested OK.

[meritosari]

Re: Dell inspiron N7110 LCD no back light

The only thing that I thought, could be that the voltage come from panel itself, and need signal at pin 36 to generate small sircuit and make 19v pulling down and then make panel be working

after all this, we don't know is it safety for KBC or not. I see you get access to touch KBC chips, Do you feel the KBC get warm?

And That thing is beyond my knowledge

We need for any advise from other tech guy

[bigsam731]

Re: Dell inspiron N7110 LCD no back light

The chip is warm but nothing out of the ordinary. I think it might be a defective IT8518. I might leave the cable the way it is and maybe change the chip at a later time.

[budm]

Re: Dell inspiron N7110 LCD no back light

Pin 36 (LED_EN, PDF page 15, 19) is the same as BL-ON pin, <1V = Backlight LED off, >2.5VDC = Backlights LED on. This BL-ON command signal comes for the main board to tell the LED backlights circuit to turn on or to turn off, so it looks like the mainboard is not sending the command signal to allow the pin 36 to swing high toward the 3.3VDC. I would use 470 Ohms resistor between Pin 36 and the 3.3V power supply, never connect anything directly unless you know for sure how the circiut functions.
Since you are able to force on the backlights AND the cable is still connected to the main board, it means that the pin 36 may have the open circuit back to the main board where the switched transistor and the pull up resistor are otherwise you would not have been able to force on the backlights, the transistor must be in the OFF mode right now, if it is on that would have damaged the transistor when you jump pin 36 directly to pin 2 (3.3VDC supply) and the pull-up resistor is not in the circuit right now either to pull the pin 36 high to make the backlights come on, if the resistor is present and the transistor is off, the backlights should be on without forcing on pin 36 with 3.3VDC.

[bigsam731]

Re: Dell inspiron N7110 LCD no back light

Thank you for the reply. When I connected pin 36 wire to pin 2, I disconnected from the motherboard side. So the backlight is only getting power(3.3V) from pin 2. When I looked at the schematics for the motherboard, pin 36 is suppose to have 3.3V from IT8518. But it has 19V for some reason and I don't know why.

[budm]

Re: Dell inspiron N7110 LCD no back light

Thank you for the reply. When I connected pin 36 wire to pin 2, I disconnected from the motherboard side. So the backlight is only getting power(3.3V) from pin 2. When I looked at the schematics for the motherboard, pin 36 is suppose to have 3.3V from IT8518. But it has 19V for some reason and I don't know why.

What did you use for the GND ref for the meter when you measure the DCV on pin 36 with the cable back in place?
I see the LVDS connector on sheet 18 of the SCH, PIN 36 is named LED_BAK, I see that it goes to sheet 23 of SCH to pin 18 of IT8518.

[bigsam731]

Re: Dell inspiron N7110 LCD no back light

I used different GND and I still got 19V on pin 36. And yes that is the only connection I see between pin 36 on pg. 18 and pin 18 of IT8518. However, there is a resistor (R472) on page 18 that is between the two pins. I might be wrong but I don't see any other connections there. I don't understand how IT8518 is supplying 19V to pin 36 unless its coming from somewhere else.

[budm]

Re: Dell inspiron N7110 LCD no back light

I doubt that you are getting 19V otherwise lots of components in that section would have been damaged including the circuit in the backlight control circuit.
The key point in this case is that the DCV on that pin 36 should toggle between <1V for LED OFF and >2.5VDC for LED on.
That 10K resistor between pin 36 and the circuit GND is there so the input at pin 36 will not be floating, it is terminated with 10K (R472) Ohms, you should read the DCV between that 10K (r472) legs to see what you have.