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[SOLVED]820-3115 missing LCD_BKLT_EN

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Fizzl92

Member
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
 
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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.
 
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Fizzl92

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!
 
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Fizzl92

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
 
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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.
 
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Fizzl92

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?
 
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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.
 
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Fizzl92

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?
 
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Fizzl92

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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