A1989 820-00850-A no backlight

Hi,

I have an A1989 820-00850-A, that after display replacement, it losed the backilght. I've tried with the old screen (broken display but full working), and now it also dosen't have backlight with the old display.

It boots to the loading bar with normal backlight, but after a while, before the bar full loads, and just before the login screen appears, the backlight decreases.

Probably something went wrong on the replacement, but I can't see nothing damaged.

Can you help?
 
Last edited:

2informaticos

Administrator
Staff member
So you can't increase the backlight with touchbar controls?
Did PRAM and SMC reset?
May have a problem with the ALS.

Just in case, try DFU revive.
 
Hi,

I can increase the backlight with touchbar, but it is not enough. It can't even notice but I can see the bar increase.
The strange think is that when I boot the Mac in diagnostic mode, the backlight stays on (OK) until I shutdown the Mac. I tried living it on for 2 hours and it always was normal for that time.
 

2informaticos

Administrator
Staff member
"Did PRAM and SMC reset?"
???

"May have a problem with the ALS."
You should try another known good LCD assembly.
At least change security settings and test booting Windows from USB.
 
Hi,

I already disabled the Automatic Light Sensor on macOS settings, and tried with an USB macOS, with the same result. Already done NVRAM and SMC reset without success.
Booting from a Windows USB always fails, and already tried WIN7 and WIN 10.
 
Hi,

I saw in some forums that this model has problems with the serialization (don't know if makes sense). Can it be something related with that?
 

2informaticos

Administrator
Staff member
Something happened in the screen replacement process.
I didn't hear someone else to get similar problem.
Shouldn't be software issue; even more, after DFU restore and macOS reinstallation.
 

2informaticos

Administrator
Staff member
The strange thing is that problem appears only when macOS load drivers.
That makes me think about ALS.
Any error comes up starting in diagnostic mode?

Check for knocked of components, or broken traces.
 
HI,

Yes, the problem only appears when Mac load drivers (just before the ending of the loading bar, and always at the same point). If left on the diagnostics mode, the backlight stays normal forever.
The diagnostic mode doesn't present any error.

I've done a lot of checking, several times, and I can't see any knocked components or broken traces, or anything damaged.

Any other ideas?
 
HI,

Right now, the display isen't recognized any more. When I connect an external display, it doesn't recognize the internal display, and the login screen appears on the external display.
 

2informaticos

Administrator
Staff member
So you've lost image on internal LCD even before loading macOS?
DP_INT_HPD no present anymore?
Check 3V3/5V_S0SW_LCD, at least in the first seconds.
 
Yes, the macOS loads directly to the external display. No image shown on internal LCD.

I don't have DP_INT_HPD (0V), but I have 1.7V on XDP_ DP_INT_HPD (not sure if it matters).

3V3_S0SW_LCD = 3.3V
5V_S0SW_LCD = 5.1V
 
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