820-00840 missing CPU VCore, fan spins no post

bcherdak

Member
Hi guys, I have a here a 820-00840 missing ppvcccpu_s0g

The USB-C meter is going from 5V to 20.5V and is pulling around .12A

The fan spins, and the trackpad starts to click when pressed but is unable to boot

I am getting USB activity, when plugging in a usb-c adapter with a apple mouse the usb is showing activity with the red laser. (on a western digital easystore it blinks the light)

CPU is getting very little warm,

and also U3900 is getting a little warm, it is under-filled and looks very clean.

U3100 -
CPUVR_VCC - 13V
CPUVR_IN - 5V
ALL_SYS_PWRGD - 3.22V
PM_PGOOD_CPUVCC - 0V
CPUVR_FCCM - 0V
CPUVR_PWM1 - 2.52V
CPUVR_PWM2 - 2.52V
VR_HOT_L - 0.9V
------

PPBUS_G3H - 13.05V
PPDCIN_G3H - 20.37V
PP5V_S5 - 5.11V
PP3V3_G3H - 3.41V
PP1V_S3 - 1V
PP3V1_RTC - 3.1V
PP3V3_S5 - 3.32V
PP1V8_S0 - 1.8V
PP3V3_S0 - 3.3V

PPVCCCPU_S0G - 0V

Any ideas? I am planning to replace the u3100 as I watched other videos from Rossmann and he replaced it, (even tho it is edgebonded all around) and it allowed the machine to work.

Please let me know what other measurements you would like me to give.

Photos attached.
 

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Last edited:

bcherdak

Member
External video? If no, probably the usual dead CPU

its not fully booting up so there cannot be external video??

also, if theres usb activity, such as light, doesn't that mean that cpu is not dead, but instead another chip not fully activating it?

Are there are chips or points I should test?
 

2informaticos

Administrator
Staff member
I doubt the board is working with 0.12A only.
Uneless your meter doesn't show real values.
If you really get Link lED flashing on bootable USB, board should be starting.
In such case, why not checking for external video too?
But again my doubt, how the board will work without VCORE (PPVCCCPU_S0G)???
 

bcherdak

Member
I doubt the board is working with 0.12A only.
Uneless your meter doesn't show real values.
If you really get Link lED flashing on bootable USB, board should be starting.
In such case, why not checking for external video too?
But again my doubt, how the board will work without VCORE (PPVCCCPU_S0G)???

Its the same usb c meter that rossmann uses and sells on his website. (https://store.rossmanngroup.com/inde...amp-meter.html)

Thats what I am confused by, there is a faint light on the mouse, not super bright.

I just checked for external video and there is none.

I am not sure why there is no vcore.

Are there any other rails I should post voltages or ohms readings for more information?

I am thinking about replacing u7100 just incase.
 
Last edited:

JohnB8812

New member
No VCore is going to be bad ISL95828 aka the picture you showed or bad CPU especially with no liquid. My bet is CPU as USBC Macs happen to often be trash
 

2informaticos

Administrator
Staff member
As you get S3 and S0 votages, U7100 is OK, don't touch it.
Apart of CPU VCORE, which other coils have no voltage?

20V/0.3A is other thing; normal value for working board.
Check VCORE at the same time, if pulse at least.

I didn't complain about meter; it fluctuates and you probably can't read all values...
 

bcherdak

Member
No VCore is going to be bad ISL95828 aka the picture you showed or bad CPU especially with no liquid. My bet is CPU as USBC Macs happen to often be trash

I will purchase from his store the chip and replace it, there was some liquid damage around the backlight area that was repaired, mostly the caps were burnt.

R3772,R3771, U3780, were replaced. C8461 (and the other big ones were replaced)

Another spot that gets hot is the u3900, not hot but slightly warm with the FLIR. with your fingers its not recognizingly hot.
 

2informaticos

Administrator
Staff member
"there was some liquid damage around the backlight area"
That's sounds like dead CPU.
There are many CPU data lines, which can be affected; even inside the board (internal copper layers).
 
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