00928 image but no backlight

[grmacs]

I've tested this with known good screen and also different LCD cable. At first I thought simple U8400 issue so replaced. No change as LCDBKLT_EN_L is not getting pulled down. SDA/SCL lines diode tests good and resistors are good.

No edp_bklt_en. Discovered cap broken but still present next to U8500. Replaced it C8504 and U8500. Getting 5V on pin 6 U8500.

Also diode of L8410 .8 with screen connected.

Checked resistance R9827 it is good.no signs of liquid or anything odd at SMC.

 

[2informaticos]

Tried PRAM and SMC reset?

Lid sensor problem should block image too, but is better to check U5255 signals.
Also check R8450-53 and their traces.
Post voltage and diode mode on SCL/SDA lines.

Be sure to get 5V at pin 45 of J8500.
Use schematic for refference.
I don't see U8500 pin 6 and C8504 there.

 

[grmacs]

Pin 6 of U8500 is PP5V_S0SW_LCD also I do get 5V at J8500-45 I misread my notes the cap that was broken off solders but still next to them that i replaced =C8509

I get 3V42 for left and right SMC_LID

Neither resets helped R8450-3 all check out. Diode for SDA/SCL @U8400 = .504 for both.

 

[2informaticos]

You may have problems with U9800, or PCH.
EDP_IG_BKLT_EN goes high?

 

[grmacs]

No, I mentioned in original post that EDP_IG_BKLT_EN is not present.

 

[2informaticos]

Are you really sure???
"No edp_bklt_en"
Pay atention to signal names...

 

[grmacs]

Ahhh. got it thanks. Nothing there either. I checked diode is .62 there.

 

[grmacs]

I swapped U9800 and still image no backlight. Is this one a lost cause you think?

 

[2informaticos]

Seems that U9800 doesn't receive backlight enable from PCH.
This is strange, if you get image on its LCD.
There may a bad communication between PCH/SMC/U9800 and T-CON.

 

[grmacs]

Is there another signal I could use to trigger backlight instead? Customer would be happy if I could get backlight working even if it changed power consumption or it stayed on when it normally wouldn't. Could I pull enable on U8500 from LID or wake signal?

 

[2informaticos]

No way like that.
Backlight requires more than simple enable signal.
U8400 must talk with T-CON through I2C bus; J8500 pins 24 & 26.
PWM backlight adjust lines go from T-CON to U9800 and SMC; pins 14 & 16 of J8500.