820-01598 pulsing rails

dudipupan

Member
Hi,

I'm working on a MBP 820-01598 with pulsing rails. All rails up to PMU_ONOFF_L seem to pulse. PMU_ON_OFF_L itself is stable at 3.3V. PPBUS_G3H is cycling from 12.6V to 12.3V. PP3V3_S5 and following rails are steady 0V.
Resistances on big coils seem to be good.
No signs of lliquid on the board. It had some burnt components on PP5V_G3S_ALSCAM that i replaced. Already checked rails for short to grounds but didn't found anything obvious.
Any ideas what's going on here?

Thanks
 

dudipupan

Member
I did checked the voltages when the Board was all allone when I recognized the rails are pulsing.
Didn't checked USB activity yet.
 

2informaticos

Administrator
Staff member
If power rails are pulsing even on board alone, I doubt you can get USB activity.

Do you have steady 20V on USB-C ports?
All AWAKE and SLPS2R voltages present and stable?
If yes, try DFU...
 

dudipupan

Member
Yes I'm getting steady 20V on bozh USB-C ports.
Checked only PP1V8_AWAKE (since the other probe points are hidden under the T2 shield next to the SSD and i want to avoid removing it and raflowing the SSD acidentally) and this rail is pulsing too.
 

dudipupan

Member
Took a closer look on PP3v3_G3H and PP5V_G3H. PP3V3_G3H is present and stable. PP5V_G3H is dropping to 4.7V every few seconds, rising up to 5.1V again.
 

dudipupan

Member
I know but unfortunately the shield goes over T2 and U7800 - including the coils.
But I was able to measure PP1V8_SLPS2R and PP1V8_AWAKE on QE000 and QE001.

Yes I did but was not able to enter DFU mode.
 

2informaticos

Administrator
Staff member
Be sure to follow all the steps in the tutorial; use correct USB-C port.
Try with Catalina and Big Sur on second Mac.
If still not recognized, then you have a problem with T2, or some AWAKE, or SLPS2R voltage is missing.
 

dudipupan

Member
Checked only PP1V8_AWAKE (since the other probe points are hidden under the T2 shield next to the SSD and i want to avoid removing it and raflowing the SSD acidentally) and this rail is pulsing too.
I already know that PP1V8_AWAKE and PP1V8_SLPS2R are missing/pulsing. I dont think the others are stable. Sorry for the badly readable post!
 

dudipupan

Member
After many many tries I was able to enter DFU mode. Think it just needed to be perfect timing because of the pulsing rails.
I revived it but it aborted with error message "Unexpected device state "DFU" expected "Recovery"".
But rails are not pulsing anymore now. Got all rails stable up to PP3v3_S5. All S5 rails are missing.
 

2informaticos

Administrator
Staff member
Try restore instead and reinstall macOS.
Be aware, this will erase internal SSD.
Ask the client if has important data, or security copy done first.
 

dudipupan

Member
Already asked that - no important data to save on this board :)
I'm getting the same error message when trying to restore.
It takes constant 0.17 amps now. I can't power it off - it just restarts after a second.
 

dudipupan

Member
PPVCCQ_ANI_SSD0: 1.8V
PP0V9_SSD0: 0.9V
PP2V5_NAND_SSD0: 2.56V
SSD0_VR_P2V5_PGOOD: 2.5V
SSD0_PMIC_RESET_L: 1.8V

All stable... seem to be good.
 
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