Technical Support Macbook pro A1990 820-01814 no Backlight

user61596

isa198585
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Reputation:

Macbook pro A1990 820-01814
The Proble is not Flexgate or LCD.
The Board looking under Microscope fine.
how can I check cbtl06142eee and LP8548B1SQ_-03 ?
What can be Problem more?
Thank you
 

user61596

isa198585
Registered
Golden

Reputation:

where is the location of backlight IC, my be your mean U5450?
backlight fuse is ok.
 

LagaDatorUmea

Lagadatorumea
Registered
Golden

Reputation:

some one?
Have u tried with another screen?
Have u tried with an HDMI cable on an external screen?
Check Fuse 8400?
Did u check VIN, and Enable signal for Display IC U8400?? Check Pin 17(Enable signal), R8447 (PWM) and check Pin 5 & Pin 18.
Checked voltage on L8410?

Post all measurements here for us to see
 

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user61596

isa198585
Registered
Golden

Reputation:

Have u tried with another screen?
Have u tried with an HDMI cable on an external screen?
Check Fuse 8400?
Did u check VIN, and Enable signal for Display IC U8400?? Check Pin 17(Enable signal), R8447 (PWM) and check Pin 5 & Pin 18.
Checked voltage on L8410?

Post all measurements here for us to see
No I don´t tried HDMI cause, cause I get image on the screen, I dont get the Backligth, I think its will be work with HDMI.
Fuse 8400 get 12.62V
PIN 17 0,00V
R8447 (PWM) 0,00V
Pin 5 have 5,12V
Pin 18 have 5,12V
 

user61596

isa198585
Registered
Golden

Reputation:

check all voltage without lcd and lvds cable . you can en backlight with jumping but user cant control of backlight brightness
Hosein Abi, I am so sorry, I tried all this time with out LCD and LVDS cable.
So now when I tried with LVDS Cable and conected LCD, I get this result
PIN 17 3.32V
PIN 18 5,12V
PIN 5 5,12V
F8400 PIN 1 and PIN 2 12,62V
 

LagaDatorUmea

Lagadatorumea
Registered
Golden

Reputation:

and yes Tried another screen, same result, nothing has changed, no Backligth
Hosein Abi, I am so sorry, I tried all this time with out LCD and LVDS cable.
So now when I tried with LVDS Cable and conected LCD, I get this result
PIN 17 3.32V
PIN 18 5,12V
PIN 5 5,12V
F8400 PIN 1 and PIN 2 12,62V

R8447 (PWM) 0,00V

1. This is a resistor: u need to check its resistance.. and post it here. should be 10K.
2. also check the feedback circuit, the resistors.
3. Checked voltage on L8410?
 

user61596

isa198585
Registered
Golden

Reputation:

R8447 (PWM) 0,00V

1. This is a resistor: u need to check its resistance.. and post it here. should be 10K.
2. also check the feedback circuit, the resistors.
3. Checked voltage on L8410?
R8447 is 9,96k
L8410 0,00V
how to get backligth with jumping?
 

LagaDatorUmea

Lagadatorumea
Registered
Golden

Reputation:

1. What voltage do you have on Gate pin for Q8400?

change U8400 IC... to a new one.

Your issue is no voltage on L8410 0,00V. Did u measure on both sides of the coil?
 

user61596

isa198585
Registered
Golden

Reputation:

q8400 get 0,00 on all pins.
the Fuse F8400 is burned, the pin number 1 on F8400 is shurted to GND, I no have Thermal Camera, any idea how to find shurt?
when I make jumping on F8400, I get 12,62V on Q8400 pin numer 4.
U8400 was already changed, nothing is changed.
What can I do more?
L8410 yes I measure on both sides of the coil 0,00V
 

LagaDatorUmea

Lagadatorumea
Registered
Golden

Reputation:

check resistance on R8401/02, so they are correct ohm.
You need voltage(lower than pin 4) on the gate(pin3) of Q8400 for it to open.

Post new measurements here
 

LagaDatorUmea

Lagadatorumea
Registered
Golden

Reputation:

U need to check the resistors (voltage divider), you need less voltage on the gate for Q8400 to open. Its a P-channel!

You should have on R8401 = 80.6k and R8402 = 63.4k, also check the capacitor(c8400) in capacitance mode, you need 1000pf.

Check them and post here your new measurements?
 

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user61596

isa198585
Registered
Golden

Reputation:

Oh yes, you are rigth, but the voltage diferent with pin 4 and pin 3 it is verry low.
pin 4 = 12,62v
pin 3 = 12,52v
C8400 =1,00 nf (1000pf)
R8401 = 80.6k
R8402 = 63.4k
 

LagaDatorUmea

Lagadatorumea
Registered
Golden

Reputation:

Oh yes, you are rigth, but the voltage diferent with pin 4 and pin 3 it is verry low.
pin 4 = 12,62v
pin 3 = 12,52v
C8400 =1,00 nf (1000pf)
R8401 = 80.6k
R8402 = 63.4k

You need to have around 5,6v on The gate(pin 3) of Q8400 for it to open.

did u check continuity mode from R8402(pin2) to the IC(u8400) pin 11? You might have a broken trace. check pls

Did u change the IC(u8400) from another motherboard same series? it needs to be the same IC, same year etc.
 
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