820-00281 no display

BCN_Techs

Member
Got mbp 15 A1707 touchbar with water damage. There was damage near lcd area and short on U7220. Changed it and now machine seems to start ( 20V 1,5-2,5Amps). No shit on lcd connector and FPC:


I checked and see that EDP_BKLT_EN is 0V so it's not enabling backlight , right?


This signal is generated by U9800 checked and it's not generating 0V on R9827.


The problem is that it doesnt start even with external monitor. I dont know what this machines do when you connect external monitor and boot them.


Also it's strange that CPU is getting just warm and GPU stays cold.


Any idea?
 

BCN_Techs

Member
P.S. SOme additional details:

Seems that machine is not getting in S0:

Once it's "on" i can listen battery charging sound when reconect charger. also touchbar is off.
 

BCN_Techs

Member
All previous message is nothing.


I was checking about S0 and see that:


PPVCC_S0_CPU - is shorted to ground. Same thing happens with PPVCCGT_S0_CPU.

P.S: PPVCCIO_S0_CPU is ok and PPVCCSA_S0_CPU is ok too.


Dead CPU?

???????Can fans sping if the cpu is dead?
 

2informaticos

Administrator
Staff member
"PPVCC_S0_CPU - is shorted to ground. Same thing happens with PPVCCGT_S0_CPU."
I'll be not so sure.
Probably very low values as normal; compare with similar board.

However, overvoltage via U7220 is a good reason to have a dead CPU now...
 

BCN_Techs

Member
I dont have known good logic board just donor one and resistance to ground is 300Ohms, with one i am repairing is 0,5V so i think it's shorted. What if i inject 1V there? Anyway if it can be only dead cpu there is nothing to loose.


Anyway it's first time i see that logic board with dead cpu is starting fans, getting 2 amps and cpu is getting warm. is that normal?


P.S: PPVCC_S0_CPU is getting 0,02 V :D
 

2informaticos

Administrator
Staff member
CPU has several power rails.
It can get warm even without VCORE.
If is really bad, then will heat abnormal without its main power.
Resistance (ohm mode) at VCORE should be at least 1 ohm; maybe much more for this board...
 

2informaticos

Administrator
Staff member
"Which line is Vcore?
-----------------------
PPVCC_S0_CPU"
We use VCORE as generic term for CPU core power...
 

2informaticos

Administrator
Staff member
Less than 1 ohm at VCORE (ohm scale) is very bad; usually dead CPU.
Lift one side of all CPU coils and check where the low value remains...
 
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