A2159 - 820-01598 - Macbook Pro 13" 2019 - Turns on, but no video or backlight.

ronaldo

Member
Hi everyone.
I got this MacBook 850-01598 to repair and it first came with no power.
Found liquid on Battery flex cable and some corrosion. The cable was replaced and Mac started and went to the system, but only on the external Monitor.
Checking the LCD FPC connector from the screen side it also had a bit of corrosion.
Now I'm not getting backlight and even video. Normally when there is no backlight I still can see very dimmest video on the screen if I use a torch. In this case no backlight and no display.
Trying to figure out the problem I found that on R5252 I'm getting 1.8V on side 1 and 0 on side 2. The resistor is ok with 100K, so U5250 is not getting Enable signal.
I'm using the board with only LCD screen connected (New screen).
I'm a newbie with a bit of knowledge.
Please can someone point me in some direction?
I2C_DISP_LS_EN - 0V
PP3V3_S0SW_LCD_R - 0V
R0541 - 0v
R0540 - 0v
 

2informaticos

Administrator
Staff member
First of all, welcome to the forum!

Do you still get external video?
If not, check for USB activity.
Also post L7210/20 voltage after 10-15s from connecting charger.
No need of internal LCD for these checkings; test the board alone on the desk.
 

ronaldo

Member
First of all, welcome to the forum!

Do you still get external video?
If not, check for USB activity.
Also post L7210/20 voltage after 10-15s from connecting charger.
No need of internal LCD for these checkings; test the board alone on the desk.
Hi.
Yes, it works fine on external monitor.
Both USB-C ports working.
Taking 20V on USB ports
 

2informaticos

Administrator
Staff member
Check diode mode to ground on EDP data lines of J8500; w/ and w/o LCD connected (no power).
Compare the values for EDP_AUXCH_P/N first.

BTW, write directly on the reply box, instead of clicking Reply button.
I don't see any reason to quote an entire post, visible few centimeters above; thanks.
 

ronaldo

Member
Without LCD
1 EDP AUXSH N - 0
3 EDP AUXCH P - 0.307
4 EDP PANEL PWR BUF EN - 0
7 EDP ML N<0> - 0.322
9 EDP ML P<0> - 0.357
13 EDP ML N<1> - 0.353
15 EDP ML P<1> - 0.356
16 EDP BKLT PWM - 1.044
19 EDP ML N<2> - 0.332
21 EDP ML P<2> - 0.359
25 EDP ML N<3> - 0.324
27 EDP ML P<3> - 0.339
With LCD
1 EDP AUXSH N - 0
3 EDP AUXCH P - 0.307
4 EDP PANEL PWR BUF EN - 0
7 EDP ML N<0> -can't measure with lcd connected
9 EDP ML P<0> - can't measure with lcd connected
13 EDP ML N<1> - can't measure with lcd connected
15 EDP ML P<1> - 0.356
16 EDP BKLT PWM - 1.089
19 EDP ML N<2> - can't measure with lcd connected
21 EDP ML P<2> -can't measure with lcd connected
25 EDP ML N<3> - can't measure with lcd connected
27 EDP ML P<3> - can't measure with lcd connected

Pin (4 - EDP PANEL PWR BUF EN) if I measure from J8500 it gives the value as 0, but if measured from pin 8 on U8500 it gives the value 1.909
 

2informaticos

Administrator
Staff member
Seems to have a problem with EDP_AUXCH_N line.
Classic problem caused by leakage from backlight output.
Nothing to do, CPU's eDP output being damaged...
 

ronaldo

Member
Big thanks to you.
That's bad news for the customer, but at least I know that there is nothing else to try to fix this board.
 
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