Hello Guys, I`m sorry for English Input. I don't know Russian.
Hopefully someone can give me guidance.


I`m dealing with MBP 15" - i7. Logic board 820-2915-A.

After trying LED replacement it came with NO Backlight & No Image on the screen. But it works on External Screen.

I checked the FUSES all are OK.
I replaced the LP8550 WLED Driver (Big pain until I manage to replace this BGA chip ) but still no backlight and matrix is not turning on.

I made some measurements. And it looks like Wled Driver is not getting ENable voltage,
Enable voltage is controlled by PPBUS_SW_BKL=PPBUS_SW_LCDBKLT_PWR, I don`t have any voltage on that line.

Also R9731=300k and R9715=100k are OK.

When I look that line it is giving power to the WLED Driver and LED Display after boost diode.

This 12V rail is controlled by Q9706 P-MOSFET which should be open with 0V on its gate. R9788 is holding it CLOSED with continuous 12V.



On other side Q9707 is with 2 x N-MOSFETS which are closed all the time and waits LCD_BKLT_EN & BKLT_PLT_RST_L signal to turn then ON so they can open Q9706 and give the 12V to PPBUS_SW_BKL



BKLT_PLT_RST_L signal is 3.3V and it`s opening halp of Q9707 but other half is waiting Positive voltage from LCD_BKLT_EN, like LOGIC AND.

LCD_BKLT_EN - signal should come from U9600 which is mystery for me what this GMUX chip does. And how it can be related to BKLT Enable signal.



Does anyone have idea what can be causing this MOSFET to DO Not turn ON. And how it can be such mess after LED replacement. I had burned fuses before but such a mess like this is hitting me for first time.

I`m attaching the Schematic if you want to digg in.

I`m out of ideas guys, please advice.

G.

I think, you have to look to old LCD, may be your MB doesn't see your new LCD or You have to look EDID signal by oscilloscope.

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Вы никогда не сумеете решить возникшую проблему, если сохраните то же мышление и тот же подход, который привел вас к этой проблеме.
Альберт Эйнштейн

Thanks for the reply Сергей, I tried with 3 LCD's and 2 different cables same problem. It`s not getting Matrix to tun on 3.3V and Backlight 12V.

For me it looks like GMUX u9600 chip is not giving Output signal to turn on LCD.

Interesting ting is also, when I force Q9706 in OPEN state, I can see only Matrix turning ON, without BACKLIGHT and without any image on the screen. So even if screen is ON by shorting Q9706 DRAIN and SOURCE there is no picture.

If it was regular laptop, not apple. Then this signal is controlled by graphic card, and after reflow it comes back. But here, GMUX is giving signal from GPU to LCD panel. GMUX opening is controlled by chipset.

Where should I look for EDID signal on Screen connection? Or U9701 - WLED driver inputs?


Thank you for participating Сергей, I`m stuck with this one. And still cannot understand how screen replace can do such big damage. Normaly only fuse or WLED chip is burning.

LCD can not turn on for 2 reasons: no platform initialization and MB doesn't see LCD. Detect matrix is ​​just the bus EDID is basically a i2c bus, and it goes to the connector of the LCD.
Essentially it's just a bus to the EEPROM which stands in the LCD and contains information about the LCD and its modes. I would later come to work and see the scheme to be more precise.

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Вы никогда не сумеете решить возникшую проблему, если сохраните то же мышление и тот же подход, который привел вас к этой проблеме.
Альберт Эйнштейн

happen, so we get the experience

_________________
Вы никогда не сумеете решить возникшую проблему, если сохраните то же мышление и тот же подход, который привел вас к этой проблеме.
Альберт Эйнштейн

this is very significant, and it suggests that the platform of the connected LCD unsuspecting and therefore does not knowingly signals to start

_________________
Вы никогда не сумеете решить возникшую проблему, если сохраните то же мышление и тот же подход, который привел вас к этой проблеме.
Альберт Эйнштейн

Check if the chip works u9270

Check if the chip works u9270