820-01958 - No power - Power cycling 20V 1.7A

[ronaldo]

Hi. Please I really need help with this.
Can't figure out the issue.

Here I have an 820-01958 that came with no power.
After my first diagnostics found U7800 getting very hot.
The voltage on the charger was 20v, varying from 2W to 3W and 0.200A.

After replacing U7800 the voltages are.
With battery
20.9V
34.59W
1.700A
But the voltage on the charger keeps cycling for a minute before it stays steady.

All these rails keep cycling for about 1 minute, then stays on.
The voltage on the charger port also keeps cycling,

L9060 - PVCCSSD0_PHASE - 2.53V
L7670 - PP5V_G3S - 5.10V
L7690 - P3V3G3H - 3.29V
L7030 - CHGR_PHASE1 - 12.7V
L7400 - VCCINAUX_RTN - 1.82V
L7230 - PPVCC_CPU_PH3 - 1.8V
L7220 - CPUCORE_SW2 - 1.8V
L7210 - CPUCORE_SW11.8V
L8410 - PPVIN_SW_LCDBKLT_SW - 0V
L8100 - P1V1_PHASE - 0.68V

All these rails keep cycling for about 1 minute, then stays on.
The voltage on the charger port also keeps cycling,

I've tried to revive it in DFU and it goes all the process without problem, restarts, and shows the Lock sign on the other Mac.
Power Cycling video from USB-C charger

 

[ronaldo]

PPBUS_G3H = 12.66V NOT CYCLING
PP3v3_G3H = 3.28V NOT CYCLING
PP1V8_SLPS2R = 1.8V CYCLING FOR A MINUTE
PP1V8_AWAKE = 1.8V CYCLING FOR A MINUTE
PP1V1_SLPS2R = 1.1V CYCLING FOR A MINUTE
PP0V8_SLPS2R = 0.79V CYCLING FOR A MINUTE
PP3V3_AWAKE = 3.29V CYCLING FOR A MINUTE
PP1V2_AWAKE = 1.2V CYCLING FOR A MINUTE
PMU_PVDDMAIN_EN = 2.03V NOT CYCLING
P3V3MAIN_PGOOD = 3.03V NOT CYCLING
PP3V3_G3H_RTC = 3.28V NOT CYCLING
PCH_RTC_RESET_L = 3.0V NOT CYCLING
P5VG3S_EN = 1.8 V CYCLING FOR A MINUTE
PP5V_G3S = 5.10 CYCLING FOR A MINUTE

PP3V3_S5 = 3.29V CYCLING FOR A MINUTE

PP1V8_SSD = 1.8V
PP0V9_SSD = 0.90V
SSD0_RESET_L = 1.80V

 

[2informaticos]

Any history available?
Inspect audio board/flex and touch ID for corrosion.

Test the board disconnecting audio flex.
Check USB activity, or Caps Lock reaction.
Also ckeck if gives external video; w/ and w/o internal LCD connected.

 

[ronaldo]

The customer stated that it suddenly stops to turn on.
Trackpad clicks, but no display.

No external video.
All voltages were taken w/o the audio board connected.
Caps lock has no reaction.
USB activity (Light on the USB Stick turns on, but keeps cycling same as the board is doing)

 

[2informaticos]

Do you get 1.7A from charger without battery connected?
Which big coils get voltage?

 

[ronaldo]

Fan spins for a second while it's cycling for a minute.
After it stays on 20V, 1.9A.

But sometimes if connect battery and power it will not cycle and goes straight to 20v, 39W, 1.945A

All this coils.
L9060 - PVCCSSD0_PHASE - 2.53V
L7670 - PP5V_G3S - 5.10V
L7690 - P3V3G3H - 3.29V
L7030 - CHGR_PHASE1 - 12.7V
L7400 - VCCINAUX_RTN - 1.82V
L7230 - PPVCC_CPU_PH3 - 1.8V
L7220 - CPUCORE_SW2 - 1.8V
L7210 - CPUCORE_SW11.8V
L8410 - PPVIN_SW_LCDBKLT_SW - 0V
L8100 - P1V1_PHASE - 0.68V

 

[2informaticos]

1.9A without battery is really high current.

Check DC voltage on output pin of the coils, not on SW side.
Compare voltages with good working board.
PLT_RST_L goes high?

 

[ronaldo]

Sorry, I mixed the context above.
1.9A is with battery connected.

PLT_RST_L - 0V - Without battery always 0V - With battery connected it happened once after a few minutes 1.8V cycles for less than a sec and on DC was 0.9 A.
PP1V8_PRIM_PCH - 1.02V

 

[ronaldo]

I left it plugged to DC and battery for about 10 minutes. (I was with a customer and I forgot to disconnect)
Now on DC I'm getting 20V and 2.02A.
Heat Sink and surrounding is burning hot.

 

[2informaticos]

PLT_RST_L must be high to boot the board.

Did you left the board on in the shell, with fan connected?
Which is CPU core voltage, when heatsink gets hot?

 

[ronaldo]

When left it in shell, it had the fan connected.

CPU core voltage when it's hot is 1.8V and PLT_RST_L also 1.8V

 

[ronaldo]

There is a different behaviour today, but I haven't done anything yet.

It has now a power cycling on PLT_RST_L.
It stays cycling for a few minutes and on the other mac where I have the Apple Configurator it keeps showing lock sign and cycling.

 

[2informaticos]

I suspect bad CPU.
The fan doesn't help too much on these machines.
It doesn't blow the air through the CPU heatsink.

 

[ronaldo]

OK. This will be a donor board for now.
Thanks for your help.