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]

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.

No they are connected. I just don't know what powers pin 36.

 

[jarotech]

Pin 36 is controlled by the IT8518 chip, pin 36 is an output of this chip, so, what is the voltage on the R472 resistor?

 

[bigsam731]

Pin 36 is controlled by the IT8518 chip, pin 36 is an output of this chip, so, what is the voltage on the R472 resistor?

On one side i get 19V and the other i get 1.4V

 

[jarotech]

The side of the R472 connected to ground, you should read 0 volts, maybe the resistor is not connected properly to ground.

 

[bigsam731]

I re-soldered the R472 resistor but got the same reading. I wonder why I get 19V instead of 3.3V pin 36.

 

[jarotech]

Another thought, when you measure the voltages, the screen is it connected to the motherboard? And what is the number of your screen.

 

[bigsam731]

Another thought, when you measure the voltages, the screen is it connected to the motherboard? And what is the number of your screen.

Yes it is, otherwise as soon as I turn on the machine it gives me 8 beeps for no screen connections or LCD failure. Also I still get no back light when I try a different LCD. I tried my LCD in a different laptop and it works just fine.

 

[jarotech]

And what is the model number for your screen?

 

[bigsam731]

And what is the model number for your screen?

samsung LTN173KT01

 

[jarotech]

From the specifications of your screen, on pin 36 you should have 3.3 volts for the screen to be enable. I think the chip (IT8518) on page 23 who control this pin is defective. A test you can perform, but this is on your own if something goes wrong, but trust me, you have to open the wire for the pin 36 on the cable from the motherboard, and connect this wire going to pin 36 to the screen to the pin 2 off the connector, in that way you give 3.3 volts to pins 36 for the screen from pin 2.

 

[bigsam731]

I did some thing similar today. I took R472 out of circuit and tried to give pin 36 3.3v from external power source. But before I did, I remeasured pin 36 it's still had 19V. I didn't want to give it too much voltage. I also measured pin 18 of IT8518 and of course I had 19V. I think I have a defective IT8518. I'm going to try out you theory tomorrow, since I have another cable anyway, and see if I get some light on that LCD.

 

[bigsam731]

From the specifications of your screen, on pin 36 you should have 3.3 volts for the screen to be enable. I think the chip (IT8518) on page 23 who control this pin is defective. A test you can perform, but this is on your own if something goes wrong, but trust me, you have to open the wire for the pin 36 on the cable from the motherboard, and connect this wire going to pin 36 to the screen to the pin 2 off the connector, in that way you give 3.3 volts to pins 36 for the screen from pin 2.

OK... I did what you said by rewiring pin 36 and attached it pin 2 and and I FINALLY have back light. I Know its a bad soldering job but I figured I"ll give it a try. Here are some pics...

https/drive.google.com/open?id=0B4eDDk7o_vmnYUV6R2JxcmpwUHo3OS1CTWJWUkc0b082cnhB
https/drive.google.com/open?id=0B4eDDk7o_vmnSlNrR3J3SEd6M0RJaEdxZXBWRVZNbHB0S05B

 

[jarotech]

Good job, put some tape on it to isolate and leave it like that, in this way it's better than changing the chip IT8518.

 

[bigsam731]

LOL. As tempted as I'm to change that chip I think I'll just settle for the tape. Who knows, I might get the urge next week and change it.
Thank you for all your help. I really appreciate it.

 

[jarotech]

Until the next problem.