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820-2936 Water Damage, Brain Dead!

computercaverva

computercaverva

Member
The board has a history of water damage showed up very corroded in the top edge of the board. The backlight circuit was hit the hardest. After cleaning the board gets a green light and fan spin however there is no chime, RAM beeps, or light on USB mouse. The CPU gets slightly warm after being plugged in for a long time however does not immediately get boiling. I have all S0 rails except for CPU_VCORE.

PPBUS_G3H: 12.59v
COMPUTING_ISNS: 12.58v
PP5V_S0: 5.015v
PP3V3_S0: 3.297v
PP3V42_G3H: 3.475v
PPVRTC_G3H: 3.302v
PP1V8_S0: 1.799v
PP1V5_S0: 1.514v
PPVCCSA_S0_CPU: 0.904v
PP1V05_S0: 1.055v
PPVCORE_S0_CPU: 0v
PPVCORE_S0_AXG: 0v
 

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computercaverva

computercaverva

Member
The clock chip was replaced and the computer now POSTs and loads the OS. The backlight circuit which was hit the hardest with the corrosion is know a problem. The LVDS was replaced due to it missing legs. The LED backlight drive has been replaced as well as all the surrounding resistors (nasty looking) The through hole via for the LCDBKLT_PWR_SW had to be rebuilt, the feed back circuit is intact, I am not getting BKL_PWM (0v). I have tried PRAM resetting it SMC lid is 3.4v and I get 12.56v to the LVDS connector pin 21.
 
D

dukefawks

Administrator
Remove R9704 on tie BKL_PWM directly to 3V on see if backlight is back. If yes then PCH is bad and best to just leave it on full brightness like this.
 
computercaverva

computercaverva

Member
I injected 3 volts into pad 2 of where R9704 was and am still getting no backlight. Should I be looking at the LVDS for not telling the computer theres an LCD present or is it more likely a problem with the LED backlight driver not getting another rail it needs to be doing its job?
 
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