[SOLVED]820-3209 pp3v3_s3

rob777

Member
Laptop would power on and got a screen on external monitor. No screen on laptop and no trackpad but keyboard does smc resets.
Started measuring power rails, found pp3v3_s3 is only 1.5v wherever I measured. Obviously.
Ended up at R7811, looked shit. Changed it. Laptop worked screen came on trackpad worked. Turned it off to put back together.
Then upon reboot, same symptoms came back. Measured R7811, pin 1 pp3v3_s3_fet_r is 3.3v
Pin 2, pp3v3_s3 is 1.5v instead of 3.3v

I replace R7811 again and still only 1.5v pin 2.

What is it that I'm missing here, feel like it's blazingly obvious..
Thank you.
 

rob777

Member
no corrosion anywhere I could find under scope. After looking at the schematic though and having fixed another one recently the same way I came to the conclusion to change the lcd cable on this one too. Low and behold problem solved. Second time an lcd cable has fixed something.
Really confused still though how it kept burning R7811, I just don't get it.
Anyway, I am thankful to you!
 

dukefawks

Administrator
Any short on 3V3_S3 will take out that resistor. 3V3__S3 goes to the LCD so it is possible the cable had an intermittent short.
 
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