820-01700 - No power - 20V 0.8A

[ronaldo]

Hi.
Got this Mac to repair which has no signs of liquid. No previous history.
Battery is dead, but I tested with a good working battery and still same.
PPBUS_G3 - 12.7V
PP3V3_G3H_RTC - 3.38V
PP1V8_SLPS2R - 1.8V Cycling.
T2 is glowing from one side and cycling.
SLPS2 and Awake is all cycling.

PP1V2_S3 - 0.082 On a good board it measures 0.160 and FlexBV 0.223

Do you think that would be an issue with the RAM modules?
Thanks

 

[2informaticos]

Test board (0.160) has the same RAM capacity?
You may have lower reading for 32GB than 16GB.

All U7800 LDOs cycle?

 

[ronaldo]

• LDO0: 0.8V Cycling
• LDO1: 3.0V Cycling
• LDO2: 1.2V Cycling
• LDO3: 1.8V ~ 1.78V
• LDO_RTC: 1.5V Stable
• VOUT_RTC: 3.3V ~ 2.69V
• LDO_CORE: 1.5V

 

[2informaticos]

Did you check diode mode to ground on all coils?
Don't forget L9080/580.

 

[ronaldo]

I forgot to mention at the beginning.
I've checked all the coils in diode mode and all seems fine.

 

[2informaticos]

You may have problems with T2, or U7800.

 

[ronaldo]

U7800 replaced an same issue.
Revive gets stuck on Installing system.
Do you think the T2 ic itself is faulty or it still could be software?

 

[ronaldo]

In DFU mode before staring Revive option all the power lines mentioned above are stable.
As soon as I press Revive or Restore it starts to cycle again.

 

[2informaticos]

Be sure to connect battery with some charge on it.
Possibly problem appears when DFU try to power SSD.

 

[ronaldo]

Good battery. Tried revive and still same.

 

[ronaldo]

Is it possible to replace the T2 on this?

 

[2informaticos]

Is possible, but think if is worth the job.
You also need to get the WiFi chip from same donor board; with its ROMs.
Of course SSD data is lost.

 

[ronaldo]

Data is not important on this device.
Shop is dead at the moment just a few jobs.
I will try that and post back.
Thanks for you help.

 

[ronaldo]

Could it be an issue with the T2 ROM?

 

[ronaldo]

T2 and it's ROM replaced.
Exactly same behaviour.

I also tried to flash another firmware into the ROM chip and with a firmware from another board it goes to DFU and when I try to Revive it. the LDOs cycle once and then Revive fail.
I try to change the firmware with the original board SN and same as mentioned above. I use the Mac EFI Toolkit.
So flashed the original firmware and back to LDOs cycling.

 

[2informaticos]

No need to flash another dump onto SoC ROM.
Good enough to erase it; should be reflashed in DFU process, if completes.

Go for restore, instead of revive.
Be sure to connect a battery holding some charge and good trackpad also.

 

[ronaldo]

I have tried with a second known good battery and another trackpad and presents same behaviour.

 

[2informaticos]

Bad NANDs maybe...