[SOLVED]820-3115 missing LCD_BKLT_EN

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Fizzl92

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Hello,
as always sorry for my bad english:rolleyes:. I have a problem with another 820-3115-B. It runs perfectly fine - it only has no backlight. I followed this path to LCD_BKLT_EN which is 0V. This is renamed to LVDS_IG_BKL_ON which comes from the PCH. I assume that because everything else works on this machine the PCH is working fine. At this point i don´t know what to do or maybe i missed something.
Thank you for your help.
Regards,
Felix
 

dukefawks

Administrator
You 100% sure have an image? If yes, check if SMC_LID is high. Could be pulled down by a bad battery indicator or corrosion on that connector.
 

Fizzl92

New member
The owner said that is was water damaged but i can´t find any evidence of water on the board. I´m sure i can see the apple and the language selection menu (i´m using a fresh installed drive). I´ll check SMC_LID tomorrow and let you know. Thank you very much!
 

Fizzl92

New member
You mean the green lights with the button on the side of the machine? Yes, i´ll mind that. Normally i take the board out of the housing while measuring. I´ll take a closer look on that commector tomorrow too.
Thank you for the advice
 

dukefawks

Administrator
C9782 would be fine and cannot cause LCD_BKLT_EN to be low!

What is resistance to GND on pin 5 of Q9707? You could ground pin 3 of Q9707 to verify if the backlight works then.
 

Fizzl92

New member
In diode mode is the resistance to ground on pin 5 of Q9707 (and pin 1 of R2055) 0,520V. If i ground Pin 3 to pin 1 of Q9707 nothing happens. Also if i ground pin 3 of Q9707 to an actual screw hole nothing happens. I measured the resistance (pin 3 to ground with jumper in place) to verify i shorted it right and it was 0,002V in diode mode. With the jumper (pin 1-pin 3) is removed i get on Q9707 pin 1,4,5,6 =0V, Pin 2=3,324V and pin 3=11,92V. On Q9706 i get: Pin 3=12.10V, Pin 4=12.6V and pin 1,2,5,6 are something between 4,3 - 5V and slowly rising (don´t know where it stops). With the jumper back in place i get on pin 1,2,5,6 straight 12.58V as it should be (with an LCD connected still 12.58V and no backlight) So i assume everything here is fine except for LCD_BKLT_EN.
I followed the 12.58V to D9701 where it should be much higher but it still measures on both sides of D9701 12.6V. On U9701 BKL_EN is 3,111V, PP5V_S0_BKL is 5V, PP3V3_S0_BKL_VDDIO is 3,3V and PPVOUT_SW_LCDBKLT_FB is 12.58V which is all fine i think. Means this that U9701 is also dead?
 

dukefawks

Administrator
Are you measuring LCD_BKLT_EN without an LCD connected? LCD must be connected for all these measurements. Remove any mods you did to Q9707 and measure voltage on D9701 with an LCD connected.
 

Fizzl92

New member
I guess i can just apologize at this point for wasting your time. I normally measure it with an LCD connected but as i need to flip the board around i disconnected it this time if i mention right:(. Now i get all signals right at Q9707 and Q9706 but still 12.6V on both pins of D9701. I measured with 2 different LCD´s while i was getting sure a picture. On U9701 BKL_EN is 3,112V, PP5V_S0_BKL is 5,07V, PP3V3_S0_BKL_VDDIO is 3,311V and PPVOUT_SW_LCDBKLT_FB is 12.58V. I´m not sure but is this caused by a dead U9701 that´s not boosting?
 

Fizzl92

New member
BKL_PWM is 3,312V. After all this i exchanged U9701 and it works perfektly fine! Again sorry for the wrong info and thank you very much for your help!
 
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