Dell inspiron N7110 LCD no back light

[bigsam731]

Re: Dell inspiron N7110 LCD no back light

here is a pic with voltage read.
https://drive.google.com/open?id=0B4...BZRm5iQUVFNFlZ
I also got the same readings on R472 and pin 18 on IT8518.

[budm]

Re: Dell inspiron N7110 LCD no back light

Look at your meter screen, it looks like the DCV reading is showing 18.3 mV (0.0183V), see the 'm V' on the screen, your meter is auto-range so it has the display to show you if it is showing the Voltage reading in V or mV.
So it is error in reading in your part, I know that it is impossible to have 19V present without the circuit being badly damaged, it is just common sense and you will learn.
Please study the meter user manual.

[meritosari]

Re: Dell inspiron N7110 LCD no back light

So, Its just misread

[bigsam731]

Re: Dell inspiron N7110 LCD no back light

This is why you are the expert and I'm not.

[budm]

Re: Dell inspiron N7110 LCD no back light

So the question now is that why the output is stuck low due to bad IC or may be the IC is being told not to turn on the backlights because it thinks you are on external monitor only for example.

[meritosari]

Re: Dell inspiron N7110 LCD no back light

This is why you are the expert and I'm not.

Honestly, I'm not mean like that.

Everybody have mistake, also I'm still learn from this forum. Sometimes I wonder might be there are something wrong at my advise, I really worry about that. How about if I mislead to you, then what would be happen, might be you've got damaged on whole board. That's why I said "We need for any advise from other tech guy"

And thanks to mr Budm join to discuss here and save us

[budm]

Re: Dell inspiron N7110 LCD no back light

BTW, check the resistance reading of that OUTPUT pin 18 of the IC and GND to see if it shows low resistance reading (<500 Ohms or so) or not.
Make sure to look at the meter's screen to see if it shows the reading in OHMS, K OHMS, or M OHMS.

If we cannot figure out exactly why the pin 18 is low, you may be able to use other section of the logic to turn the backlights on and off instead.

[bigsam731]

Re: Dell inspiron N7110 LCD no back light

Honestly, I'm not mean like that.

Everybody have mistake, also I'm still learn from this forum. Sometimes I wonder might be there are something wrong at my advise, I really worry about that. How about if I mislead to you, then what would be happen, might be you've got damaged on whole board. That's why I said "We need for any advise from other tech guy"

And thanks to mr Budm join to discuss here and save us

I meant what said. I fix lots of things but this is kind of a starting point for me on board repair. I'm just glad to see other people give their expertise, time, and afford to help other in my position. So please don't take this the wrong way.

Now we figure out that it was a misread on my part, thanks to Mr. Budm, I need to figure out the actual cause of the low voltage.

[bigsam731]

Re: Dell inspiron N7110 LCD no back light

BTW, check the resistance reading of that OUTPUT pin 18 of the IC and GND to see if it shows low resistance reading (<500 Ohms or so) or not.
Make sure to look at the meter's screen to see if it shows the reading in OHMS, K OHMS, or M OHMS.

If we cannot figure out exactly why the pin 18 is low, you may be able to use other section of the logic to turn the backlights on and off instead.

these are the reading that I got from both pin 18 on IT8518 and pin 36 on LCD connector.

https://drive.google.com/open?id=0B4...0xWklJWHUxNWNN
https://drive.google.com/open?id=0B4...dhd09mLUpHOGtj

[budm]

Re: Dell inspiron N7110 LCD no back light

That is low Ohms (~99 Ohms) reading for the output of the IT8518, at this point I would say that the output drive of the IT8158 is bad, it should be in K Ohms range.
BTW, your meter is showing Battery sign so your batteries may be low, I am not 100% sure, you need to check the user manual.

[bigsam731]

Re: Dell inspiron N7110 LCD no back light

So do you think that I should change that chip? Or is there any other command not coming in to turn on pin18?

[budm]

Re: Dell inspiron N7110 LCD no back light

At this point I do not believe that output circuit is good, you can read other output pins to see what kind of resistance you get just to verify, 100 Ohms reading to me is not normal.

[bigsam731]

Re: Dell inspiron N7110 LCD no back light

I'll test more pins and let you know.

[bigsam731]

Re: Dell inspiron N7110 LCD no back light

I wasn't really sure which pins to test but I test but I testes few of the them. I tested pins 11,26,95,96,21 and they all had 0 ohms.

[meritosari]

Re: Dell inspiron N7110 LCD no back light

If you want to test resistance, please make sure you didn't apply power to board.

I don't believe all those pin short to ground, if yes then your laptop can't turn on

[bigsam731]

Re: Dell inspiron N7110 LCD no back light

These are the reading I got for the same pins with no power:
11= 24.2K
21= 72.5K
26= 26.9K
95= 41.8K
96=9.2K
18=1.1

[meritosari]

Re: Dell inspiron N7110 LCD no back light

I'm still learning "label" LCD bak, on other schema has using ITE chips, and I found all have different depend design by mobo's vendor.

As Mr Budm mentioned (post #16) same is BL_ON, Yesterday I've been measuring on BL_ON pin at a few board that I have it, all of those pins I've read in K ohms, of course depend design, if connected by Resistor 10K vs GND, then be read 10K

Actually if working fine pin 36 connected from other 3V supply (in this case already connecting to pin 2 of J2) then I think it'll be fine but consider to add resistor for safety ( Budm recommend 470 ohm).
I know this is the lazy way, but working fine

there are some risk if you no have experience in replacing KBC chip

But it's all up to you

[bigsam731]

Re: Dell inspiron N7110 LCD no back light

Looking at the schematics, I don't see any other switch to turn on pin 36 besides IT8518. I think I'm going to change it in a few days and see if that is the problem. Unless someone else can tell otherwise.

[meritosari]

Re: Dell inspiron N7110 LCD no back light

you may be able to use other section of the logic to turn the backlights on and off instead.

@bigsam731
Please read this point too...if I understanding looks like only have voltage, but less / very low ampere

[budm]

Re: Dell inspiron N7110 LCD no back light

He must remove the connection back to the IC fist so it will not load down the force on Voltage, but I believe he can use other active pin to use as the BL-ON signal, i just need to look at the diagram to see which one to use.
BTW, If LVDS connector pin 2 (3) AVDD 3.3V is a switched power supply then you can use resistor between pin 2 and pin 36 and make sure to disconnect the wire going back to pin 18 (LED_BAK) of the IC then you will be all set.