820-3787 No Backlight (PPVOUT_S0_LCDBKLT shorted to GND)

[KappaDev]

Hi, I have an 820-3787 Macbook logic board taken from a 15" Late 2013 Retina A1398 Macbook Pro.

Dim image appears on screen without backlight. Image can be seen by shining bright light through back side of LCD's Apple logo or via external display.

Visually inspected both sides of board for any signs of liquid damage but there did not appear to be any nor were there any signs of damage around backlight circuitry. None of the moisture/liquid indicators were red either.

0V is present at pin 1 of the LCD connector (PPVOUT_S0_LCDBKLT) while running with LCD plugged in. Checking resistance to GND revealed 30 ohms. I assume this is shorted to GND.

Tested with known good working LCD with same results, no backlight present (0V, 30ohm to GND). Also tested without any LCD connected with similar results.

Does this sound like a bad LCD connector or more of a backlight circuit issue? Don't want to inject voltage and blow anything up

Boardview and schematics are attached.
Thanks

[piernov]

Re: 820-3787 No Backlight (PPVOUT_S0_LCDBKLT shorted to GND)

30 ohms to ground on backlight output with LCD disconnected is a partial short to ground on the main logic board yes. You could inject voltage but honestly here it's not necessary, there's only a handful of components on backlight output.
For piece of mind you can confirm that D7701 is not shorted (so that you're not measuring a short to ground before it). It is never the problem though.
First inspect very closely LCD connector for any sign of damage/burn. If nothing, remove the 6 capacitors on backlight output rail (just switch them from one of there pad to avoid losing them). If still shorted to ground, take off LCD connector.
And if that doesn't solve it either you have a short to ground inside the PCB, so at that point you can start injecting voltage to try to locate any spot of the PCB that's heating up, and dig to remove the short between layers…

[Vesko356]

Re: 820-3787 No Backlight (PPVOUT_S0_LCDBKLT shorted to GND)

I will do it this way - take off the LCD cable from the board, and measure the resistance again, if the PPVOUT_S0_LCDBKLT is still shorted (if not the lcd cable is the reason), check the D7701 if it's ok 99.99% one of the five caps (C7715 C7716 C7717 C7718 C7719) is shorted, if the D7701 is bad (shorted) just remove it, and check both pads for short to GND to understand where is the short - before or afrer the diode, if it's before check C7710 C7711 and C7712.

[KappaDev]

Re: 820-3787 No Backlight (PPVOUT_S0_LCDBKLT shorted to GND)

I will do it this way - take off the LCD cable from the board, and measure the resistance again, if the PPVOUT_S0_LCDBKLT is still shorted (if not the lcd cable is the reason), check the D7701 if it's ok 99.99% one of the five caps (C7715 C7716 C7717 C7718 C7719) is shorted, if the D7701 is bad (shorted) just remove it, and check both pads for short to GND to understand where is the short - before or afrer the diode, if it's before check C7710 C7711 and C7712.

Yup, shorted cap. Thanks guys!

[AcidFire521]

Re: 820-3787 No Backlight (PPVOUT_S0_LCDBKLT shorted to GND)

I have a similar issue.
Can someone post the locations of the mentioned caps above?
My fuse is fine and have 0v on PIN1

[hani002]

Re: 820-3787 No Backlight (PPVOUT_S0_LCDBKLT shorted to GND)

i have the same case but i found the shotkey diod D7701 measure in 2 direction
and i dont knoe from where can i find the same diod
any sugestions