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No backlight after liquid damage

B

BCN_Techs

Member
Hi,

I have 820-3115 logic board that boots and all is ok except of backlight. There were some water damaged componentes with wrong values aroung U9701 so changed them and U9701 too and backlight turned on. After a couple of hours it was off again. Checked and seems that all values are correct. The only thing i can see is that PPVIN_SW_T29BST line is shitted, some components has pins like black but there is no short to ground.

PPVIN_SW_T29BST - 2.6V


My question is PPVIN_SW_T29BST can make backlight not work propery?
 
2informaticos

2informaticos

Administrator
Staff member
PPVIN_SW_T29BST is Thunderbolt power rail and is not even enabled, untill something is connected on the dedicated connector.

I suspect bad solders under U9701; reflow it.
However, I recommend to measure some voltage around it first.
Check BKL_EN, BKL_PWM, 3/5V power, voltage both pins of D9701.
Check continuity from D9701 to ball A5 of U9701.
Also look if all resistors have good value and terminals...
 
B

BCN_Techs

Member
Checked again. all componentes around U9701 and it's all ok.

BKL_EN - 3.1 V
BKL_PWM - 3.3V
THere is continuity between D9701 to A5

Will try to change U9701 by new one.
 
B

BCN_Techs

Member
The voltage on out is 12,57V

Fixed. 2informaticos was right:)

It was continuity from A5 to D9701. The problem is that the trace was damaged righ near a5 under the chip so i didnt see it before. Restored and now working. Thanks a lot
 
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