A1989 820-00850 weird issues

[waterchill]

Good day friends,

I have actually this board here and I don't really know where to start to search. Sometimes it power on with apple logo and it is booting with full fan speed and very slow. Sometimes it is drawing current about 600-700mA fan full speed and nothing happens no screen. Tried to make diagnose but it hangs in the last minute. When it not turns on I leave it over night, then I can turn on 2-3 times. Also not possible turn on with battery. Sometimes when turn on a questionmark appears for 1-2 second and the it is booting. So maybe something wrong with ssd. I checked

PPBUS_G3H_SSD0 = 12,6V
PP2V7_NAND_SSD0 = 2,55V
PP1V8_SSD0 = 1,8V
PP0V9_SSD0 = 0,9V

 

[2informaticos]

Tried to start in safe mode?
Did you try with known good battery?

Full fans speed is usually sign of triggered temperature sensor.
Some machines may have this symptom when battery is not detected; maybe not in this case.

Check resistance over C7020/23 (ohm scale).
Also check SMC_AVREF voltage.

 

[waterchill]

I tried this mainboard in complete functional top case and still same. Also tried a working one in this top case, is also working. So it looks like it is a mainboard problem. C7020 and C7023 is both about 2,5 ohms. SMC_AVREF = 1,25V

Bott in safe not possible, it is loading till 70% and then it stuck. Today I got it one time to boot up to login screen of course with fan full speed and very slow everything. So far with this problem I was always able to boot up and check with software which sensor is bad. Without booting this will be hard

 

[2informaticos]

Try DFU revive.
If no important data, try restore too; it will erase SSD.

 

[waterchill]

Juist managed to login and started TG pro. It says GPU and hard drive temperature sensors may not be working properly. But temperatures looks ok.

 

[waterchill]

I'm also missing the point "Enclosure"

 

[2informaticos]

Are these errors reported starting in diagnostic mode?