MBP 2013 15" 820-3787 with no backlight with an image no shorts clean board.

[Wachenaggo]

I have MBP 2013 15" 820-3787 with no backlight with an image but sometimes intermittently working then off if restarted.

It sees the screen with 5v on PP5VR3V3_SW_LCD
PPBUS_SW_LCDBKLT_PWR = 12.6V
PPBUS_SW_BKL = 12.296V
PPVOUT_S0_LCDBKLT - 12v

On U7701 5v on VDDD & VDDA
BLK_SD is 8.9V
BKLT_EN is 3.3v
SCL and SDA is 4.4v~~V

Voltage reading in such.

[mon2]

Re: MBP 2013 15" 820-3787 with no backlight with an image no shorts clean board.

Good measurements.

U7701 looks to be defective. Replace it and post your update.

You can source these from AliExpress.

[Wachenaggo]

Re: MBP 2013 15" 820-3787 with no backlight with an image no shorts clean board.

I already replace it U7701 lighted once then I turn it off and put it back in the shell now the backlight lighted once then doesn't work again. help.

[mon2]

Re: MBP 2013 15" 820-3787 with no backlight with an image no shorts clean board.

Measure the voltage on both sides of fuse F7700.

If the voltage is present on BOTH pins of this fuse, measure and post the voltage readings of the following:

ISNS_LCDBKLT_P

ISNS_LCDBKLT_N

[Wachenaggo]

Re: MBP 2013 15" 820-3787 with no backlight with an image no shorts clean board.

Measure the voltage on both sides of fuse F7700.

If the voltage is present on BOTH pins of this fuse, measure and post the voltage readings of the following:

ISNS_LCDBKLT_P

ISNS_LCDBKLT_N

ISNS_LCDBKLT_P = 12.56v

ISNS_LCDBKLT_N = 12.56v

I noticed BKLT_SD is not pulling to ground. when i touch multimeter leads red on ground then BKLT_SD on black backlight turned on. then off if turned off?? replace u7701 again?? but i got backlight when touch?? also no keyboard backlight voltage help pls

[mon2]

Re: MBP 2013 15" 820-3787 with no backlight with an image no shorts clean board.

I would consider to reflow U7701 -> apply lots of flux + heat + low air pressure.

Make that part swim -> push with tweezers with a small nudge (very carefully) -> the part will push away and then return naturally onto the proper pads.

Just in case the contacts are not making; or there are shorts that you cannot see.

Then test again.

Only if U7701 spits out a low signal on pin # 11 will the gate of mosfet Q7706 be LOW enough to turn on this P-channel mosfet. With P-channel, the gate must be more negative than the voltage on source & drain to enable.

What is the voltage on LCD_BKLT_EN and BKLT_EN_R ?

[Wachenaggo]

Re: MBP 2013 15" 820-3787 with no backlight with an image no shorts clean board.

I would consider to reflow U7701 -> apply lots of flux + heat + low air pressure.

Make that part swim -> push with tweezers with a small nudge (very carefully) -> the part will push away and then return naturally onto the proper pads.

Just in case the contacts are not making; or there are shorts that you cannot see.

Then test again.

Only if U7701 spits out a low signal on pin # 11 will the gate of mosfet Q7706 be LOW enough to turn on this P-channel mosfet. With P-channel, the gate must be more negative than the voltage on source & drain to enable.

What is the voltage on LCD_BKLT_EN and BKLT_EN_R ?

I replaced it again with a new IC I double-check the connection and no shorts are found.
R7700 and U7701 are connected = 12.56v
LCD_BKLT_EN = 3.3v

BKLT_EN_R = 3.3v

BKLT_SDA = 4.9v
BKLT_SDA = 4.9v

Feedback resistor are good i can adjust brightness when jumped on BLKT_SD.
PPVOUT_S0_LCDBKLT =45.7v is supposedly 55v??
LCDBKLT_EN_L = 11.9v
BKLT_SD = 7.7v wrt gnd
R7702 & R7701 are good also
PPVOUT_S0_KBDBKLT = 15.5v is supposed to be 40v???
also tested SMC_LID is good when i placed the magnet it turned off then I had to jump the BKLT_SD to turn it on again
head scratch what did i do wrong. also -04 version compatible on -03 version. because i have a original -04 from a1502 2014 tho just wondering

[Wachenaggo]

Re: MBP 2013 15" 820-3787 with no backlight with an image no shorts clean board.

So i Replaced Q7706 it turned on and works so it the P Channel mosfet but another things left is the keyboard backlight is not working i have 15.5v?? no short tho.?? good R7783

R7747 BKLT_PWM_KEYB pin 2=.85 and SMC_SYS_KBDLED pin 1=0.85

[mon2]

Re: MBP 2013 15" 820-3787 with no backlight with an image no shorts clean board.

1) Check the status of:

KBDBKLT_RETURN1 @ R7723, pin # 1 & #2
KBDBKLT_RETURN2 @ R7724, pin # 1 & #2

2) With no power, meter in diode mode, check the condition of D7720.

3) With no power, meter in resistance mode, confirm the Iset resistor used for the keyboard backlight @ R7741 (BKLT_ISET_KEYB) - is the resistance = ~31k ohms ?

[Wachenaggo]

Re: MBP 2013 15" 820-3787 with no backlight with an image no shorts clean board.

KBDBKLT_RETURN1 @ R7723, pin # 1 = 0.2v & #2 = 0.22v
KBDBKLT_RETURN2 @ R7724, pin # 1= 0.2v & #2 = 0.22v
red probe wrt PPVOUT_S0_KBDBKLT

i think the resistor is good

D7720 0.178v red probe on anode black cathode OL on reverse

R7741 32.4kOhm

is there i miss??

[mon2]

Re: MBP 2013 15" 820-3787 with no backlight with an image no shorts clean board.

KBDBKLT_RETURN1 @ R7723, pin # 1 = 0.2v & #2 = 0.22v
KBDBKLT_RETURN2 @ R7724, pin # 1= 0.2v & #2 = 0.22v
red probe wrt PPVOUT_S0_KBDBKLT

Red meter probe on the resistor pin # 1.
Black meter probe to ground.

Apply power to the logic board to measure the voltage.

The diode reading looks low to me.

Can you check the resistance of the diode ? Remove all power, meter in resistance mode.

See attached.

[Wachenaggo]

Re: MBP 2013 15" 820-3787 with no backlight with an image no shorts clean board.

fully boot on login screen 5.02v @pin1 with webcam plugged in
the PPVOUT_S0_KBDBKLT = 5v again

119.6 ohms at forward bias

[mon2]

Re: MBP 2013 15" 820-3787 with no backlight with an image no shorts clean board.

Confirm the following voltages (meter in DC volts; 20v is ok):

(Red meter probe on point to test; Black meter probe to ground)

BKLT_SDA
BKLT_SCL

BKLT_SDA_R
BKLT_SCL_R

I2C_BKL_1_SDA
I2C_BKL_1_SCL

See attached - confirm the feedback leg for the keyboard is not damaged. This trace appears to be a via from one side of the PCB to the other so confirm the trace / via is not damaged. You can remove all power, meter in resistance mode -> check the resistance from one side of the PCB to the other side (check at the via).

[Wachenaggo]

Re: MBP 2013 15" 820-3787 with no backlight with an image no shorts clean board.

BKLT_SDA = 4.98v
BKLT_SCL = 4.96v

BKLT_SDA_R =4.92v
BKLT_SCL_R = 4.92v

I2C_BKL_1_SDA = 3.3v
I2C_BKL_1_SCL = 3.3v

it has continuity from PPVOUT_S0_KBDBKLT to u7701 pin 8

also i got LCD backlight =46v but not KB Backlight = 5v

[mon2]

Re: MBP 2013 15" 820-3787 with no backlight with an image no shorts clean board.

The keyboard backlight is known to be good ?

Swap out L7720 from a donor board. If available, also D7720.

[Wachenaggo]

Re: MBP 2013 15" 820-3787 with no backlight with an image no shorts clean board.

it works before working LCD backlight and no water damage in the logic board. ill try to salvage an L7220 and D7720 tomorrow ill report back once i changed it. maybe it got burned?? while replacing U7701 like 6 times before getting it placed perfectly??? IDK. I ended up shorting pads on the 2nd-5th try to solder the new chips. is that possible to get burned? or maybe the backlight sheet overheated don't have a spare tho. I got confident I can't remove R7701 without removing the logic board on the shell. it gets wrinkled a little bit? but not burn a hole?

but before that, i got it 1st try with a new chip but the issue was i get backlight but again dead when I get it to shell fully reassemble but i remember LCD BKLT and kbd bklt is not working so I replaced, again and again got frustrated, i thought it was the u7701 but its the p channel mosfet but still no kb bklt.

[mon2]

Re: MBP 2013 15" 820-3787 with no backlight with an image no shorts clean board.

Before all of this next stage, you can try:

a) remove R7747 - it is only a 0 ohm resistor but is 0402 size. If it is lost in the process, you can always use a blob of solder to bridge the same location on the PCB. Use flux + heat + low air pressure so the part(s) do not go flying. Then with tweezers, push it away but gently off the pads. Then no one gets hurt (ie. no ripping or tearing of the pads).

This part will have to be removed for the next test since the SMC is also sending out a PWM stream of pulses. We do not want to challenge the SMC output with our own.

b) once R7747 is removed, consider to apply a 3v0 to 3v3 power rail onto R7747, pad # 2. This will mimic a full ON intensity for the keyboard backlight.

This rail can be sourced from somewhere on the board that is using 3v0 to 3v3. DO NOT go higher than 3v3 for this rail.

First measure the voltage you plan to use for this signal and then solder the wire to the location.

Or you can use an external DC power supply that will be dialed up to 3v0 ~ 3v3.

Then black of power supply to ground on the logic board.
Red wire of power supply to R7747, pad # 2.

Does this force the keyboard backlight to be ON and visible ?

[Wachenaggo]

Re: MBP 2013 15" 820-3787 with no backlight with an image no shorts clean board.

problem was solved by replacing L7220 from a donor board. maybe it got burned from changing u7701 many times. Thank you very much @mon2.