820-01041-A no backlight

Dozer

Member
i just work on this machine, no much experience with this model.

i can see the picture but no backlight

I bought a new display because i thought the problem is the backlight flex cable but same problem

so i measured the IPD_LID_OEPN, if closed has 0V if open has 1.8V
PP3V3_S0SW_LCD has 3.3V
PPVOUT_S0_LCD_BKLT is 0V

F8400 is ok and the area around u8400 looks normaly

all the board is first time out of case and no liquid or similar to see

is this a known comon problem?
 

Dozer

Member
when I start the machine and light a bright light on the screen i can see what happens. I see the apple logo and then the user account.
but now i saw that there is no touchbar activities. the tb should light up when comes up the user account isnt it?
 

Dozer

Member
still no progress in this case

EDP_BKLT_EN = 3.35V and R8442 is 0 Ohm
BKLT_SCL/SDA lines both have .529

external Display showing good
2 NEW Displays tested for working in other machine, working good, with this machine no backlight
 
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Dozer

Member
so, if PPVOUT_S0_LCD_BKLT is 0V then 8400 is not switching on or PPVOUT_S0_LCD_BKLT is short to GND

in diode mode PPVOUT_S0_LCD_BKLT to GND is .804

F8400 is ok

maybe LCDBKLT_EN_L is not working, how it is switching from U8400 SD-Pin? should be Low if turned on isnt it?
 

2informaticos

Administrator
Staff member
U8400 must pull down BKLT_SD.
But requires correct communication through I2C_BKLT bus; apart of high EDP_BKLT_EN.
 

Dozer

Member
checked now
PPVIN_S0SW_LCDBKLT_R is 12.93V, is ok in my opinion
LCDBKLT_EN_L is as well 12.93V should be zero i think?

ah ok, just read your post 2informaticos

so I checked R8450 and R8451 both 0 Ohm
and R8452 and R8453 both 1.8Ohm
 

Dozer

Member
i disconnected the display and checked pin 26 and 24 on the flex cable
both 5.01V but on scope no communication to see may be because display is not connected
 

Dozer

Member
ok. so i soldered now 2 cables on C8553 and C8554 build in the board and signals are there
scl has a clock and sda has data signals
 

2informaticos

Administrator
Staff member
If these signals, as BKLT_EN_R, arrive to U8400, you should have backlight.
If not, check all traces, solders and components around U8400.
 
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