820-02443 - No power 5V 0.010A

[joesklar]

Hi there,

I have a faulty board. The meter is reading anywhere between 5.020 - 5.040V and 0.000 - 0.030A. The amp reading seems to suggest it is power cycling somewhat...

I tested U5700 and I'm getting the correct voltages. In fact I am getting PPBUS_AON.
Around U5200 PPDCIN_AON_CHGR_R I am getting only 5V. Does this suggest an issue with the CD32 chips?

I tested all USB-C connectors with the same readings.

Any help is appreciated!

 

[2informaticos]

Any history available?
What about 3V8_AON and U8100's LDOs?

 

[joesklar]

I originally replaced the screen. Since replaced, sold on eBay. The customer returned it after 1 month, when I got it back it is in this state. There were no known issues with the board.

3V8_AON - 3.8V

I'm not sure what to probe around U8100. What is an LDO? If you can tell me what to test I can provide the readings.

Many thanks

 

[2informaticos]

Low Drop Output (LDO) rails are clearly marked on pages 42 (Master PMU) & 38 (Slave PMU).

BTW, don't bother with the ones marked "NC" (Not Connected)!

 

[joesklar]

Thanks for the explanation!

Here are the voltages I think I have them all covered.

U7700:
PP1V8_S2 - 0.3-0.4V fluctuating
PP1V2_S2 - 0.3-0.4V fluctuating
PP3V8_AON_SPMU_ISNS - 3.8V
PP1V5_AON_VCORE_SPMU - 1.5V
PP1V2_AON_SPMU - 1.2V
PP1V8_AON_SPMU - 1.8V
PP1V2_AWAKESW_BLC - 0.0V
PP0V72_S2_VDDLOW - 0.140 - 0.170V fluctuating

U8100:
PP3V8_AON_MPMU_ISNS - 3.8V
PP0V8_S2_CLVR_VDDDIG - 0.200 - 0.240 fluctuating
PP3V3_AON - 1.7 - 1.9V fluctuating
PP1V8_S2SW_CLVR_VDDC1_LDO - 0.380 - 0.460V fluctuating
PP3V3_S2 - 0.9 - 1.1V fluctuating
PP1V2_S2 - 0.360 - 0.460V fluctuating

 

[2informaticos]

Check PMU_VDDHI behavior.
Also check diode mode to ground on U8100's missing LDOs; disconnect any power first.

 

[joesklar]

Hi,

PMU_VDDHI
R8170 pin 1: 12.340V, pin 2: 2.580V
R8171 pin 1: 2.580V, pin 2: 0.0V

U8100 diode mode readings
PP0V8_S2_CLVR_VDDDIG - 0.313
PP3V3_AON - 0.423
PP1V8_S2SW_CLVR_VDDC1_LDO - 0.517
PP3V3_S2 - 0.413
PP1V2_S2 - 0.294

 

[2informaticos]

2.58V at PMU_VDDHI is good enough; if you don't detect any drop on it.
I asked about its behavior just to confirm if is stable.

In this case, all U8100 LDOs should also be stable.
You may need to replace it.

 

[joesklar]

Thanks for the feedback.
I have never replaced a BGA chip this large before. Even if I could perform the work, where can the chip be sourced from? Does it need to come from a donor board or can it be ordered online?
In your experience is specialised equipment needed or can it be done with a standard microsoldering set up?

Thanks

 

[2informaticos]

Such chip replacement, needs good practice.
Is very easy to damage the chip, even the mainboard.
14" and 16" models have interchangeable PMUs.