820-00840 not turning on

[chedda]

Hi,

This is what i gathered so far about this board:
- No liquid damage visible
- No image, no chime, no trackpad clicking, no caps led
- No image on external monitor
- 20V at USB-C Voltmeter, The current goes to ~500mA at first, after a couple of seconds goes down to ~220mA and stays there
- ALL_SYS_PWRGD is 3.19V, PPBUS_G3H and _S0 rails mostly present, only found these suspicious:
PPVCC_S0_CPU is 1V, then drops to 0.6V when current goes down to 220mA,
PPVCCSA_S0_CPU is 1V, then drops to 0.8V, when current goes down to 220mA,
PPVCCGT_S0_CPU is 0V (no display attached)
- On thermal camera:
CPU cooler around 43°C (no fan attached)
U2800 around 55°C
U3900 around 50°C

Are U2800 and U3900 damaged or are these temperatures normal? How would I rule them out (don't have a donor board at hand)?
Where should I go from here?
Thanks
BR

 

[2informaticos]

First of all, welcome to the forum!

"PPVCC_S0_CPU is 1V, then drops to 0.6V when current goes down to 220mA,
PPVCCSA_S0_CPU is 1V, then drops to 0.8V, when current goes down to 220mA"
Looks like CPU starts working.

"PPVCCGT_S0_CPU is 0V"
iGPU voltage will not appear until high load graphics.

There should be some fault history.
Check for USB activity (not only power), as described in the forum (several times).
Test the board alone on the desk, just for USB activity; no other shell device connected.

 

[chedda]

Thanks.
If I plug in a battery powered controller on the second port with the voltmeter, it shows 4.7V and 0.4A.
I assume this is what you mean by activity (didn't really find a description)

 

[2informaticos]

NO!
Use a pendrive (or external SSD) with macOS preinstalled.
If Link LED (must have one) flashes, USB activity is confirmed 100%.

 

[chedda]

I created an external drive with macOS as you said and don't have USB activity (blinking Link LED) on this board.
What now?

 

[2informaticos]

Drop voltage on CPU coils looks normal, like booting.
Seems that board gets stuck.

You didn't say anything about how the fault appeared yet.

 

[chedda]

Unfortunately i don't have any info. The seller on ebay doesn't reply.

 

[chedda]

OK, i Just got a reply. It fell on the floor.

 

[2informaticos]

Drop machine is a nightmare.
Probably broken traces/solders under some BGA chip (CPU?)...

 

[chedda]

Any way to find out which BGA chip or which to rule out?
Or isn't it worth the trouble?

 

[2informaticos]

Looks like hopeless project.

 

[chedda]

Ok, thanks