820-4924-A - Work fine but no image on LCD

[GoodguyFR]

Hello, I have a A1502 with a 820-4924-A that is working well when plugged in Display Port on external display. With internal display plugged in I have no image on it (but still on external display). The Apple Logo on the back cover is ON when the OS boot is over and I have PPVOUT_S0_LCDBKLT = 40V, which supposed to mean that the LCD is not seen. The LCD is not cracked and both connector and cable looks good. The board also looks good.

So far, I have replace the LCD cable, the LCD assembly and finally the LCD connector, still have PPVOUT_S0_LCDBKLT = 40V

Here some measurement on J8300 :
- PPVOUT_S0_LCDBKLT = 40V
- PP3V3_S0_EDP_R = 3.3V
- PP5VR3V3_SW_LCD = 5V
- PP3V3_S0_LCD = 3.3V
- I2C_TCON_SCL = 0V
- I2C_TCON_SDA = 0V
- DP_INT_ML_P<0> = 0V as <1>, <2>, <3>
- DP_INT_ML_N<0> = 0V as <1>, <2>, <3>
- DP_INT_ML_C_P<0> = 0.46V as <1>, <2>, <3>
- DP_INT_ML_C_N<0> = 0.46V as <1>, <2>, <3>

No short on J8300, FL8300 to FL8303 seems fine, all DP_INT_ML lines have continuity. Could 40V on PPVOUT be a logic board problem or is it often because of the display/connector ?

Thank you for your help, I really hope the problem doesn't come from U0500.

 

[2informaticos]

Is retina display, so 40V is OK.
Check all C832x capacitors and traces.
Also try known good COMPATIBLE screen.

 

[GoodguyFR]

Ok so it's a good news if 40V is normal, all my power rails seems to be fine on the LCD connector. I'll try an other assembly as soon as I find an other one.

When you say "check all C832x", you mean check for a short on the pins or there is an other way to check a capacitor ? All traces between C832x and F830x are fine (bip in diode mode).

 

[2informaticos]

Check if no component is knocked off.
Also check diode mode to ground on these caps; on the CPU side.

 

[GoodguyFR]

Every components are present. Diode mode on these caps gives me 0.267. Does someone have a good 820-4924 to confirm me these values ?

Also, I measured EDP_BKLT_PSR_EN and EDP_PANEL_PWR_OR_PSR_EN on U8330, I have both 3.3V. I ordered a new assembly, I'll give you some news as soon as it arrive.

Finally, I'd like to correct my previous measurements on I2C_TCON_SCL and I2C_TCON_SDA, they are both 3.3V.