820-4924-A No Backlight

[machelper]

Hello everybody;

I m working on 820-4924 (Retina 13" 2015) no backlight problem, No liquid damage or drop. Tried another known good LCD and data cable.

- F7700 = ok and 12.5V
- Replaced U7700 nothing change
- BKLT_EN_R = 3.3V
- PPVIN_S0W_LCDBKLT_R 12.5V ok
- LCDBKLT_EN_L is 12.5V ( it must be low i think)
- PPVIN_S0SW-LCDBKLT is 0v
- SMC_LID = 3.32V

where can i check next step?

 

[dukefawks]

Are you absolutely sure you have an image on the LCD?

 

[machelper]

Yes Duke. When i put the light behind lcd i can see image.

 

[dukefawks]

Check data lines continuity from LCD connector pin 3 and 4 to U7700. Check voltage on pin 8 on LCD connector.

 

[machelper]

Hi Duke,

LCD pin 3 and 4 shows 5V; LCD pin 8 is 0v; EDP_BKLT_EN is 3.3V

 

[dukefawks]

Read my question again and post your findings.

 

[machelper]

When checked dataline pin 3 and 4 connecting to u7700 without problem.

 

[dukefawks]

Are you sure you checked with a known good panel from a 2015+ model? Anything else does not work.

 

[machelper]

I dont have full case.. but i have 2015 13" LCD and old models LCD data cable its same problem no backlight
Can i put DC to DC converter like this ( http://www.aliexpress.com/item/1pc-...r-Supply-Buck-Converter-Step/32582253910.html ) and inject backlight voltage directly?

 

[machelper]

Hi again ;
I tested board with know good 2015 LCD and cable also no backlight. When checked PPVOUT_S0_LCDBCKLT to ground resistance its 72ohm is it normal? İ think its too low

Where can i check next step?