A1990 820-01814-01 no boot

[hgoncalves]

Hi,

I have an A1990 820-01814-01 with no boot.

It powers on, I have 20V on ampmeter, and it goes to 4A with battery, and 0.609A with the board on the desk alone.

Already tried revive and restore DFU with no sucess.

It has fan spin, CPU gets hot, but have no USB activity.

On big coils I get:

LA350 = 0.902V
LA300 = 1.351V
LA650 = 0.902V
LA640 = 0.903V
LA340 = 0.903V
L7231 = 0V
L7330 = 0V
L7221 = 0V
L7211 = 0V
L7420 = 0V
L7410 = 0V

Can you help?

 

[2informaticos]

Any history available?
DFU ends with error?

Compare diode mode on the coils with good board.; especially the ones without voltage.

Did you check L7700/1 and L8102 voltage?

 

[hgoncalves]

Hi, No history. It stoped working overnight client says.
DFU finishes without any message at all. Just goes to the blocket lock image after finishing the restore step 4.
Unfortunently I have no other board to test...

L7700 = 2.489V
L7701 = 1.201V
L8102 = 0.954V

 

[2informaticos]

Inspect all components around U7100.
You may have PCH, or CPU problems.
CPU_VR_EN_R comes high?

 

[hgoncalves]

Hi,

Right now it started to reboot by it self. It reaches 1.5A and power cycles.

However, now, I get 0.939V on L7231, L7221, L7330 and L7211. The only ones that remains with 0V are L7410 and L7420

Components around U7100 seam ok. CPU_VR_EN_R comes to 1.0V.

I notice that U1200 and UA600 gets hot on thermal cam, and not know if it is relevant. Is it?

 

[2informaticos]

L7410/20 correspond to iGPU; don't expect to get voltage there yet.
CPU core should drop to 0.6V aprox, when board boots.
Starts with 0.939V and never drops a bit?

How much time to reboots?

 

[hgoncalves]

It takes around 40 seconds to reboot.

Actualy, on CPUCORE SW1/2 Î get 1.125V and on CPUCORE_SW3 I have 1.248V.

On PPVCC_CPU_PH1/3 I have 0.939V and stays like that until reboot.

 

[2informaticos]

Why do you check in front of buck converter coil (SW side)?
There is no real DC voltage; check ALWAYS at the output pin of the coil, for DC voltage.
And, in case like this with 2-3 coils tied together, why do you need to check all of them?

Reflash U4770 and try again DFU restore.

 

[hgoncalves]

HI, tks, and sorry for the ignorance. Still learning...

I've never flashed U4770. I suppose that I can Use the BY-T200 to do it, but I don't have the file to flash. Do you have it?

 

[2informaticos]

You can use any BIOS programmer, with correct adapter for 1.8V and small package.
Try this one...

A1990 T2 Unlock Data.BIN

drive.google.com

 

[hgoncalves]

Hi, I managed to program U4770 with the new file. However, when restoring in DFU I get an error, and full fan spin.
Any idea?

 

[2informaticos]

Try again flashing back original SoC ROM.

 

[hgoncalves]

Hi,
Same error in DFU restore, after restoring original Soc ROM, but I just realize that now, I only get 5.16V from ampmeter.

 

[hgoncalves]

Hi,
Should I give up on it?

 

[2informaticos]

Nor even Apple has a clear response for T2 error messages.