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[SOLVED]820-3437 no backlight

Gmorb

Gmorb

Member
System had water damage replace lcd connector a bunch of corroded components pertaining to lcd backlight. And ran some wires for broken traces on backlight boost. Replaced led driver im assuming if i had bridged any balls on led driver the system wouldnt turn on? I do get an image on screen and smc_lid is high my only guess to why i dont get a backlight at this point is that BKL_EN is not getting proper voltage?

PPHV_S0SW_LCDBKLT = 8.56v
pin 3/4 of lcd connector get 8.56v
LCDBKLT_BOOST = 8.56v
BKL_EN = 2.8v

any ideas?
 
Gmorb

Gmorb

Member
Yes there was no continuity to ball a5 from feedback trace test poiny. it also came straight off when trying to add solder to it. Ill have to run a wire from test point of FB to A5 ball. PWM signal is present but at 1.4v

ill have to wait for my LED drivers to come in before i continue.

is it smart to try and dig out a pad on A5 or is it useless once it comes off?
 
Gmorb

Gmorb

Member
I replaced led driver again ran a small wire from a5 to PPHV_S0SW_LCDBKLT since the FB trace was pretty useless. I get 8.5v on that wire now but i still get no backlight is it because bkl_pwm remains at 1.4v and bklt_en is at 2.8v? Im stumped at this point.

Update: found the issue i ran a wire to the wrong point removed and all is working. I do however get this theater light effect on the bottom right side of the screen also when turning the brightness down the left side gets darker than the right Its not a big deal but im wondering if its the screen itself from the water damage or the isens resistors at fault?
 
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dukefawks

Administrator
One or more of the LED return lines are not good. Check R7717-22, could also be bad soldering on the LP8550.
 
Gmorb

Gmorb

Member
R7717 seems to be shorted to ground its trace goes under all the damage not sure if thats why? I removed it and it actually looks a lot better without it. Will there be an issue down the road without it?
 
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dukefawks

Administrator
No idea, could be shorted under the LP8550 or in the board of course. See if there is a GND ball next to the one R7717 is going to. I think it should be ok to leave it as -is if the short is in the board. It will just look shit on the LCD.
 
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