820-3437-B

[ddahlstrom]

Afterlight liquid spill, device powers on with green/orange light, and we get fan spin, but absolutely no image and no backlight visible. Took a few board measurements and tested that all power rails were present, until I noticed 0.001V present on PPVIN_S0SW_LCDBKLT_FET. So far, there is 8.6V present on pin 4 of Q7707, and also 8.6V present on pin 3 of Q7706. I probably am misunderstanding this, but doesnt there have to be a negative voltage difference between gate and source to allow transistor to turn on and allow power to flow through Q7706? I can provide other measurements if you need, but am not sure what may be the problem or where else to test. Any help is greatly appreciated!!

 

[ddahlstrom]

Also 0.001V present on PPHV_S0SW_LCDBKLT

 

[2informaticos]

Do NOT go so fast for backlight; image MUST appear first.
Check first for USB activity, probably not just video issue...

"all power rails were present"
Including VCORE and all from pages 57/58?

PLT_RESET_L goes high?

Check all SPI Bus Series Termination resistors and their traces.
Clean/remove J6100.
Try known good BIOS dump; links posted on the forum.

 

[ddahlstrom]

Not sure why the change, but after sitting down today to test the board, I currently am missing pp5v_s4rs3... (well I should say it is power cycling). If I am not mistaken, this signal comes from the charging port, so I replaced with a known-good charging board but still same issue. Do not measure a short on that line. Not sure what to do from here, but not getting the same results as yesterday and am stuck again. Thanks again for the help.

 

[2informaticos]

Test the board alone on the desk, without LIO flex connected; keep only 5 pins DC cable connected.
5V_S4 comes from L7520.
PPBUS_G3H and 3V42_G3H both stable?
Also check 3V3_S5/SUS.

Are you using original Magsafe 2 charger?