a1502 820-4924-A Liquid Damage... no image, but boots when Magsafe plugged in

papalati

Member
I thought you wanted voltage on SCL what is SCKA? I posted SCL and SDA like 2-3 comments up. You said they had to be the same.

I2C_BKLT_SCL = 5V
I2C_BKLT_SDA = 3.3V

I don't see SCKA...
 

2informaticos

Administrator
Staff member
You should get similar values on both lines, you've posted a big difference.
That could be the reason of no backlight; as it is controlled through I2C_BKLT_SCL/SDA bus.
Are the last values taken with LCD connected?
In such case, pot voltages without LCD too.

R7050/51 must be 0 ohm and R7052/53 2.4K.

Sorry for misstyping, I meant SCL, not SCKA.
I can only use aprox 60% of my eyes...
 

papalati

Member
But I'm also not getting any internal DP because the 2 displayports on the side are not exporting any image. Only the HDMI on the other side of the laptop is working.

I will get you the other measurements this evening.

Thanks again for all your help
 

2informaticos

Administrator
Staff member
Internal LCD is connected through eDP (Embedded Display Port), which is not related with external DP going through Thunderbolt.

As DP_INT_HPD stays high, and you get steady 5V at pins 28-30, PCH detects internal LCD correctly.
Very likely image is there, but not easy to detect.

Think what you did on the board, recheck all your job.
You had correct BKLT_SDA with 0V before.

The big difference on I2C_BKLT_SCL/SDA lines blocks the backlight now.
 

papalati

Member
Well, I went back to check my work and as I was checking continuity on the lcd connector pins, it looks like i have a short to ground on I2C_BKLT_SCL.

Going to have to backtrack and try to find it. I'll try to tomorrow as it isn't my work as I removed the lcd connector and jumper wires and the short was still there.

Going to sleep it's been a long day.
 

papalati

Member
So the short was bothering me. Backtracked it to U7700. Removed U7700 and the short was gone. Gonna order a replacement.
 

papalati

Member
u7700 replaced and short is now gone.

l2C_BKLT_SCL = 5V
I2C_BKLT_SDA = 5V (was 3.3v)

R7752/53 are not 2.4K they are 1.59k
R7750/01 are 0.3 ohm

still no backlight
 

2informaticos

Administrator
Staff member
"R7752/53 are not 2.4K they are 1.59k"
Is normal to get lower value indications for onboard measurments.

An o-scope can show if there is activity on I2C_BKLT_SCL/SDA and EDP_BKLT_PWM lines when backlight keys are pressed.
At least check if EDP_BKLT_PWM DC level varies.

DP_INT_HPD stays high?
 
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