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Old 10-01-2012, 07:57 AM   #1
Phoriver
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Default Need help finding LED backlight fuse [PICS]

I have an asus k53 series laptop. I cracked the lcd so I ordered a replacement from laptopscreens.com HOWEVER it was not a direct replacement. I found a slightly different asus laptop with the same screen specs (size, led, 40 pin, connector location) except for a 1080p resolution :P. After installing the screen and turning on the computer it looked like the connector wasn't on right (weird tint, etc). So I took the laptop apart again but this time I decided to test the screen before reassembly so to not have to tear it down again if it wasn't right. When I turned the computer on it still wasn't right (different tint this time) so I jiggled the connector GENTLY and after about 10 seconds of this the backlight died. Here is what I have done so far to diagnose the issue:
  1. Tried old screen, backlight not working (it was working before I took it out) leading me to think it was a problem with the cable or the motherboard
  2. Made sure it wasn't an issue with the lid switch. It works correctly.
  3. Confirmed both old and new screens working, I can see my desktop when using a flashlight. Just no back light. Also made sure windows was reading the new screen at its native rez.. all good.
  4. Tried to find a blown fuse on the motherboard around where the lcd ribbon connects. No luck, only found one fuse in the area and it passed continuity.
  5. found 4 other fuses in different areas of the board and all working.
  6. found what I think is a fuse that wont pass continuity located near the DC jack.

So my issue is basically the same as this thread http://forum.notebookreview.com/dell-inspiron-dell-studio/478489-inspiron-1545-led-screen-no-backlight-5.html

I just can't seem to find the right component, maybe there isn't a fuse and I fried something else??

Here is the connector area


same area


Closer. The component circled in red passed continuity and and no resistance so I'm assuming this is a fuse but is not blown.



opposite side in the same area, looks like its mainly the transformer area for the cpu.


Full board shots:





Here is what didn't pass continuity, I forget what the ohms were.


Everything is so damn small and not labeled!!

Links to original images:
http://i.imgur.com/EL8ru.jpg
http://i.imgur.com/RZG2r.jpg
http://i.imgur.com/O1sAo.jpg
http://i.imgur.com/ghBPZ.jpg
http://i.imgur.com/pkwk7.jpg
http://i.imgur.com/wtRYh.jpg
http://i.imgur.com/igkPg.jpg
http://i.imgur.com/2OcPe.jpg
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Old 10-01-2012, 09:42 AM   #2
budm
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Default Re: Need help finding LED backlight fuse [PICS]

Please see the pictures for test points. Black probe of the meter to the metal part of the chassis.
Attached Images
File Type: jpg LAPTOP MOSFET.jpg (761.0 KB, 706 views)
Attached Files
File Type: pdf LAPTOP MOSFET.pdf (310.1 KB, 1030 views)
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Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956

Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999

Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl

Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/

TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809
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Old 10-01-2012, 10:04 AM   #3
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Default Re: Need help finding LED backlight fuse [PICS]

Quote:
Originally Posted by budm View Post
Please see the pictures for test points. Black probe of the meter to the metal part of the chassis.
Thanks for the reply. I just want to confirm the pins I'm supposed to test. 1/2 on the input and 6/7 on the output? What should I be testing for?
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Old 10-01-2012, 10:10 AM   #4
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Default Re: Need help finding LED backlight fuse [PICS]

Yes.
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Old 10-01-2012, 10:12 AM   #5
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Default Re: Need help finding LED backlight fuse [PICS]

Am I testing with the computer on?
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Old 10-01-2012, 10:16 AM   #6
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Default Re: Need help finding LED backlight fuse [PICS]

Take the reading when the computer is off and when the computer is on. Do you still have the old LCD panel, you will need to have it hook up as well since the mother board may detect the present of the LCD panel or not. We just want to confirm that the MOSFET is turn on and send the voltage to the panel.
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Old 10-01-2012, 04:29 PM   #7
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Default Re: Need help finding LED backlight fuse [PICS]

Hey bubm, I got 3.384v on both the input/output of the mosfet and the both sides of the inductor. Any ideas?
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Old 10-01-2012, 04:40 PM   #8
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Default Re: Need help finding LED backlight fuse [PICS]

I expect 5V, but that means at least the panel is getting the power to it. Did you download the original panel spec and see what voltage it needs to run?
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Old 10-01-2012, 05:19 PM   #9
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Default Re: Need help finding LED backlight fuse [PICS]

Quote:
Originally Posted by budm View Post
I expect 5V, but that means at least the panel is getting the power to it. Did you download the original panel spec and see what voltage it needs to run?
Here is the very detailed spec sheet. From the block diagram it looks like the connector receives the 3.3v for the screen and a separate 7-21v for the led driver. However on the pinout of the connector I'm only seeing 3.3v

Edit: The led power input was on the next page.

http://www.google.ca/url?sa=t&rct=j&...otxkFQ&cad=rja
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Old 10-01-2012, 05:34 PM   #10
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Default Re: Need help finding LED backlight fuse [PICS]

There's nothing on the led power input on pins 38,39,40. 36 (led enable input) registers 0.56v
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Old 10-01-2012, 06:45 PM   #11
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Default Re: Need help finding LED backlight fuse [PICS]

OK, so the MOSFET that we tested is for supplying the power for the T-CON LCD panel. Then we need to trace out pin 39~40 to find out where they go to, the typical voltage for LEDs are 12VDC, so there must be a switching power supply somewhere on the board, also the LED Enable should be between 2.5~5.5V, so it is not being able right now.
I think you will need to find the service manual for this mother board to repair down to component level.
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Old 10-02-2012, 12:17 PM   #12
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Default Re: Need help finding LED backlight fuse [PICS]

Quote:
Originally Posted by budm View Post
OK, so the MOSFET that we tested is for supplying the power for the T-CON LCD panel. Then we need to trace out pin 39~40 to find out where they go to, the typical voltage for LEDs are 12VDC, so there must be a switching power supply somewhere on the board, also the LED Enable should be between 2.5~5.5V, so it is not being able right now.
I think you will need to find the service manual for this mother board to repair down to component level.
I've scoured the net trying to find the schematic for the board, no luck. I was hoping for something the same quality as we found for the screen.. such a big help.

I'm assuming the issue is likely origination from this location (red line indicates position of 40-pin connector)



Couple of questions (sorry):
  • Is there anything that you think I should test?
  • Is it safe to poke around for voltage? can it cause damage?
  • When testing for voltage on pins 38-40 we used the same ground as before.. should we have used the led ground pin that's located on the connector?
  • Is the component circled in red a fuse?

Thanks, I really appreciate all the help!

Last edited by Phoriver; 10-02-2012 at 12:22 PM..
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Old 10-02-2012, 12:36 PM   #13
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Default Re: Need help finding LED backlight fuse [PICS]

Is there anything that you think I should test? One way to find out where those 38~40 go to is to put the meter in the lowest scale, then put one probe on the pin 40 and just poke around the board close to that area and look for 0 Ohm reading, it has to be connected to some kind of switching power supply on the board. You will do this test with the power and batteries removed.

Is it safe to poke around for voltage? can it cause damage? Just have to be careful not to slip the probes!

When testing for voltage on pins 38-40 we used the same ground as before.. should we have used the led ground pin that's located on the connector? The connector gorunds are tied to the chassis ground and the ground plain of the mother board. so we are OK on that testing.

Is the component circled in red a fuse? The picture is too small for me to see clearly.
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Old 10-02-2012, 12:43 PM   #14
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Default Re: Need help finding LED backlight fuse [PICS]

Thanks for the super quick reply. I'll let you know how it goes!!
This is such a huge learning experience for me, I'm kind of enjoying it haha.
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Old 10-03-2012, 03:25 PM   #15
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Default Re: Need help finding LED backlight fuse [PICS]

Hi Phoriver...Thanks for referring me here! It looks like you've found someone knowledgeable....'budm'. Can see that you're making some progress, so keep up the good work! It's a bit 'heavy going' for me - but if you lead I'll follow!
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Old 10-04-2012, 12:08 AM   #16
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Default Re: Need help finding LED backlight fuse [PICS]

Quote:
Originally Posted by Phoriver View Post
Here is the very detailed spec sheet. From the block diagram it looks like the connector receives the 3.3v for the screen and a separate 7-21v for the led driver. However on the pinout of the connector I'm only seeing 3.3v

Edit: The led power input was on the next page.

http://www.google.ca/url?sa=t&rct=j&...otxkFQ&cad=rja
Wait, this spec sheet you found, is it for your original LCD or the new LCD you bought?

Maybe you can post pix of the LCD labels for each panel?

Assuming the LED backlights are off, did you / can you shine a light on the panel and see a dim image?

AFASIK, at least on computer monitors that use LED backlights, the LEDs are driven separately than the 40pin cable for signal.
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Old 11-05-2012, 02:10 AM   #17
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Default Re: Need help finding LED backlight fuse [PICS]

Hello,
I have the same problem. bought a new screen without the flashlight test.
Did you find out wich fuse it is?
Greetings Sato
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Old 01-01-2013, 11:16 AM   #18
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Default Re: Need help finding LED backlight fuse [PICS]

Hi! Did you find the fuse? I'm having the same problem.
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Old 01-01-2013, 03:27 PM   #19
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Default Re: Need help finding LED backlight fuse [PICS]

I see a resistor with 0 ohm on it. it's a kind of fuse i think. Check to see if it's open or not (have resistance of 0 ohm or not)
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Old 01-01-2013, 03:31 PM   #20
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Default Re: Need help finding LED backlight fuse [PICS]

Quote:
Originally Posted by anno View Post
I see a resistor with 0 ohm on it. it's a kind of fuse i think. Check to see if it's open or not (have resistance of 0 ohm or not)
In most cases a 0 ohm is just a jumper -- it's just shaped like a resistor so surface mount machines can handle it.
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