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Desperately need help locating motherboard component


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#1 Bluscandth

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Posted 12 June 2016 - 01:50 AM

Greetings all. This is my first post in the forum, but I am desperately in need of help.

 

I work in a repair shop and we recently took in a Dell inspiron 15r 5520 with a cracked screen. Ordered and installed a replacement, and turns out, the back light did not function. Upon troubleshooting, the backlight in the old, broken LCD is also now burnt out (It worked before), leading me to believe that there is another problem at play. These screens do not have invertors, and upon doing some googling, I discovered some dells have fuses located on the motherboard that protect the backlight circuit for the LCD. After extensive research, I cannot locate this fuse or determine any other cause for the LCDs' backlights being non-functional.

 

Thanks in advance. I would just replace the board, but I don't have $180 to replace a part I probably befuddled. I am relatively sure the cable to the lcd was plugged in with the battery in, or the ac jack plugged in.

 

Also, the LCD cable is intact. Any help is appreciated. Attached are screenshots of the board near the lcd cable connector and a link to the motherboard schematic.

 

http://www.s-manuals.com/pdf/motherboard/compal/compal_la-8241p_r1.0_schematics.pdf

 

 

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#2 technonymous

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Posted 12 June 2016 - 03:05 AM

Typically the inverter is inside the screen assembly near the bottom.



#3 Bluscandth

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Posted 12 June 2016 - 05:35 PM

Typically the inverter is inside the screen assembly near the bottom.

This laptop does not have an invertor board.



#4 JohnC_21

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Posted 12 June 2016 - 05:52 PM

Did you by chance see this dell thread showing the fuse? Seems to be a common Dell problem.

 

http://en.community.dell.com/support-forums/laptop/f/3519/t/19359235

 

Edit: Here is the link for a post by alarmrepairman

 

https://www.experts-exchange.com/questions/26865874/Blank-screen-on-Dell-Inspiron-1545.html


Edited by JohnC_21, 12 June 2016 - 05:54 PM.


#5 Bluscandth

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Posted 12 June 2016 - 06:01 PM

Did you by chance see this dell thread showing the fuse? Seems to be a common Dell problem.

 

http://en.community.dell.com/support-forums/laptop/f/3519/t/19359235

 

Edit: Here is the link for a post by alarmrepairman

 

https://www.experts-exchange.com/questions/26865874/Blank-screen-on-Dell-Inspiron-1545.html

I did see that thread, however, that fuse is not on this board.



#6 JohnC_21

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Posted 12 June 2016 - 07:27 PM

I don't know if there is a fuse on this MB. I am providing some links. Hopefully it will help.

 

http://www.laptopschematics.ro/backlight-led-screens-part-2/

 

http://www.laptopschematics.ro/?s=dell+15r

 

Click on the KBC Controller link in the second link I posted for the schematic of the 15R.



#7 Bluscandth

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Posted 12 June 2016 - 08:14 PM

I don't know if there is a fuse on this MB. I am providing some links. Hopefully it will help.

 

http://www.laptopschematics.ro/backlight-led-screens-part-2/

 

http://www.laptopschematics.ro/?s=dell+15r

 

Click on the KBC Controller link in the second link I posted for the schematic of the 15R.

Thanks, the first link gave me some more ideas for troubleshooting.



#8 Bluscandth

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Posted 13 June 2016 - 04:46 PM

I have now tested the LCD connector on the motherboard with a multi and I have found that the inv_pwr_src pin does not have any voltage. Can I be correct in assuming that the lcd has a built in inverter and that it is not getting power, hence why the screen is nearly black?



#9 JohnC_21

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Posted 13 June 2016 - 05:01 PM

Sorry, I don't have the expertise to answer that question but the inverter on a CCFL backlight is used because the CCFL needs a higher voltage. LED backlights do not require a higher voltage and therefore no inverter is required.






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