Macbook A1708 820-00840 No Backlight

[Instafixx]

Hello,
Confirmed NoB-ack Light. Display is fine - Checked on another machine - No Flexgate.
Voltage on PPVOUT_S0_LCDBKLT is 0V

Ohms Reading is keeps increasing and ultimately stops at 167.5 kOhms . Checked at C8473

 

[2informaticos]

Any history available?
Do you get image, only missing backlight?

Check 3V3/5V_S0SW_LCD and DP_INT_HPD voltage.

 

[Instafixx]

With display connected?? These are on the other side of the board

 

[2informaticos]

Nobody impede you to test the board on the desk, connecting a spare LCD assembly.

Also, if you plan to stay in this business, should get all necessary things which help your jobs.

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[Instafixx]

Thank you for guidance.

Yes i get image only Backlight missing. I can see the apple logo with a flashlight .

No history available. The board looks clean.

L7690 is a bit rusty but i get voltage there.

3V3 and 5V_S0SW is fine.

DP_INT_HPD is 3.28V

 

[2informaticos]

First step, check F8400.
Be sure all resistors around U8400 have correct ohm value (not to ground).
Pay atention to the resistors connected to SCL/SDA lines.
Also check voltage and diode mode to ground on these lines.

Post diode mode to ground readings at both pins of D8410.

 

[Instafixx]

Ohms Value ( Not to Ground)
F8400 1.1 Ohms

R8444 - 1.4 Ohms
R8410 - 13.4 Ohms
R8453 - 1.2 Ohms
R8452 - 1.2 Ohms
R8450 - 0.7 Ohms
R8451 - 0.7 Ohms
R8442 - 1.1 Ohms
R8445 - 0.7 Ohms
R8440 - 1.01 M Ohms
R8431 - 17 KOhms and keeps on increasing.
R8432 - 60K Ohms and keeps increasing ( Sometimes shows 3.8 M Ohms and decreases)

Diode Mode Reading (Red to Ground)
D8410
Pin 1 is .894
Pin 2 is 1.228

SCL/SDA line resistor is .557

 

[2informaticos]

For high value resistors, is normal to get lower readings measuring them onboard.
However, can't get short (1.2 ohm) for R8452/3.
Please, recheck their values.

 

[Instafixx]

The customer took away the device for some data backup. Will come back in a day or 2. Will update then.

 

[Instafixx]

R8444 - 0.9 Ohms
R8410 - 13.4 Ohms
R8453 - 1.34 KOhms
R8452 - 1.32 KOhms
R8450 - 0.7 Ohms
R8451 - 0.7 Ohms
R8442 - 0.9 Ohms
R8445 - 0.7 Ohms
R8440 - 1.01 M Ohms
R8431 - 17 KOhms and keeps on increasing.
R8432 - 60K Ohms and keeps increasing ( Sometimes shows 3.8 M Ohms and decreases)

Rechecked

 

[2informaticos]

"R8432 - 60K Ohms and keeps increasing ( Sometimes shows 3.8 M Ohms and decreases"
High value resistors must be measured disconnected from circuit.
Desolder one pin and check it then; is more easy to measure than out of board.

Also check all traces continuity.