No backlight. Quanta Z09 REV H DA0Z09MBAH0 Aspire M5-481PT

drewrox2009

New member
I have a quanta motherboard, computer powers on, and everything seems to be working except for the back-light.
backlight out on the lvds connector is 18.6v with or without lcd attached. no short to ground from connector.
I am assuming that the led driver is not working correctly or something is going on with the pwm signal.
The problem is that i cannot seem to find the led driver to save my life.

Computer did have liquid damage, cleaned and reflowed corroded areas, and everthing worked for over a month.
anybody familiar with Quanta boards?
 

drewrox2009

New member
I for the life of me cannot find a board view for this board, i have the labeling but being fairly ignorant with quanta boards cannot figure out how to associate this screen print to These two resistors..
and i truly feel like an idiot saying this but i cannot find u22. according to my schematic it should be TPS61187 wich is a 20QFN.

im so lost on this board.
dukefawks thank you for all the help.
 

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drewrox2009

New member
I strongly believe it is, I suppose i could be wrong, but it shows z09 on the board, and all of the research ive done cross referencing the laptop model and motherboard model point me to z09.
the forum won't let me upload images right now on my phone, macbook, or windows computer.
here is a link of the markings on the board hosted on imgur.
http://imgur.com/a/NJAZh
 

dukefawks

Administrator
I even found U22 in the photos, it is not stuffed. So the diagram does not match your model. I assume you have a regular LCD and not one with the backlight driver on the motherboard.
What is that crap on the KBC? How did this fail? LCD replacement with battery installed?
 

drewrox2009

New member
I guess i ended up with the wrong schematic. I was looking for the actual chip.
that was just a drip of flux.
the original issue with this board was no power caused by liquid damage. after corrosion was cleaned up and the board was ultrasonic'd nothing looked toasted and the computer was working fine, got back to customer for 2 weeks and the lcd would no long show backlight. reinstalled graphics drivers, made sure brightness was setup up to full. tested in PE disk. with the computer powered off i did un plug and re plug in the lcd with the battery also plugged in. Which in retrospect i know is never a good idea. but it was having this issue before disassembled.

Because of the previous liquid damage i assumed that something had gone on the board. But it definitely can be an lcd issue also.

the computer does still power on and function normally just with no backlight.

Included picture of kbc area cleaned up.

http://imgur.com/a/vAis3

I really appreciate all the help.
 

drewrox2009

New member
okay on the lcd connector i am getting
3.23v on pin 22 BL enable
3.34v on pin 23 system pwm signal input
and 18.9v on pin 27,28 and 29 backlight power.
according to their schematic they are all in spec,

so does this mean that the lcd is bad, or is there a possibility that the pwm not being generated correctly?
 

drewrox2009

New member
Thank you duke. I was pulling my hair out, thinking i was blind. i will order an lcd.
Should have double checked my schematic. Your guidance helped me get to the end days faster than i would have myself.
 
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