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?

 

[dukefawks]

So you are using a 2013 LCD cable.......yeah I'm not sure that will work, actually I'm pretty sure they are different, look at the pinout between the boards. Stop messing around and get proper test parts.

 

[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?