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

 

[bigsam731]

All the voltages are good, measure pin 2 and 4 on the LCD connector.

they both have 3.3V

 

[jarotech]

Are you certain the cable for the screen is good, because from what I deduct, all the voltages for the screen are good, you should have the backlight on.

 

[bigsam731]

Are you certain the cable for the screen is good, because from what I deduct, all the voltages for the screen are good, you should have the backlight on.

I've replaced the cable before. Could it both cables are faulty? Just to be sue I'm going to check the continuity on the cable and let you know.

 

[bigsam731]

Ok. I got continuity on all the pins on the cable except pin 1, 34, and 37. But when I lifted the protective tape, I noticed that those pins did not have wires that leads to the other side.

 

[jarotech]

The pins 1, 34 and 37 are not connected on the motherboard, so the cable don't use them.

On the connector for the screen you have those voltages on the pins.

Pin 40 - 19 volts
Pin 36 - 4.4 volts
Pin 35 - 3.1 volts
Pin 4 - 3.3 volts
Pin 2 - 3.3 volts

Also on pin 3 of the connector JP1 you have 3.3 volts.

 

[bigsam731]

This is the reading that I got in the LCD side of the cable:
Pin 40 19V
Pin 36 19V
Pin 35 3.1
Pin 4 3.3V
Pin 2 3.38

i also retested the motherboard connector side and I got the same results on all above pins.

 

[jarotech]

Are you sure you have 19 volts on pin 36 at the LCD connector? And on the connector JP1 (this is not the LCD connector), what do you have on pin 3?

 

[bigsam731]

Are you sure you have 19 volts on pin 36 at the LCD connector? And on the connector JP1 (this is not the LCD connector), what do you have on pin 3?

I remeasured again and I got 18.9V on pin 36 of the LCD connector on both sides of the cable. Also I got 3.1V on pin 3 of the JP1 connector. just to be sure the JP1 is the connector for the mouse pad correct?

 

[jarotech]

Yes, JP1 is connected to the mouse pad and also for our need the lid switch. The only different voltages are on the pin 36 of the LCD connector. I don't have the datasheet for the Embedded controller for your laptop, so I extrapolate the voltage from a similar one.

 

[bigsam731]

I got this schematics which looks really close to my board. If anyone know how to read this and figure out whats wrong with the LCD light.

https://drive.google.com/file/d/0B4eDDk7o_vmnQzdnaVk2b2swR2s/view?usp=sharing

 

[bigsam731]

Is R472 supposed to be grounded out according to the schematics?

 

[jarotech]

Yes, it's connected between pin 36 and ground, why?

 

[bigsam731]

Sorry. What I meant to say that I have ground and both sides if that resistor and have continuity through it.

 

[jarotech]

Follow the trace from the resistor R472 to the pin 36, from the schematic, they are supposed to be connected together.

 

[bigsam731]

Yes you are right. So, if I'm reading the schematics correctly, the voltage to that resistor should 3.3V and 3.2V on pin 36. But the reading was 18.9V on pin 36.

 

[jarotech]

How do you know that you should have 3.3 volts on the R472 resistor?

 

[bigsam731]

It was just a guess looking at page 23, the power coming in from pin 21 is 3.3V and going to Pin 18 which leads to R472 resistor.

 

[jarotech]

Sorry, but not quite true,on page 23, the wire from R203 which goes to pin 21, you have a red dot, that means that both wires are interconnected. You do not have a red dot between the wire from R203 and the pin 18 and pin 125, so they are not interconnected. But you should have 3.3 volts because the pin 18 is an output voltage and supplying this chip is 3.3 volts. I could be wrong, but until someone corrects me, this is my interpretation.

 

[bigsam731]

So either way we should have 3.2V where we have 18.9V on pin 36 of the LCD connector.

 

[jarotech]

Yes, you should have 3.3 volts on the R472 and pin 36 of the LCD connector. You said before that you have zero volts on the R472, but you have 18.9 volts on pin 36, you have an open trace between R472 and pin 36.