820-02020 PPBUS_AON missing

[ugamazing]

Board had no history of liquid; unsure of drop history, but no signs of damage of any kind worth noting.

Charger sitting at 5v/0a. PPBUS is at 1.9v-0.9v steady cycle (peaks, drains, loops). Confirmed CHGR_EN_MVR is missing, but DCIN was reaching ISL just fine, so replaced ISL--no change at all. Confirmed pp3v8_aon is also missing--and being unsure *exactly* which signal appears first (or if they are simultaneous), I inspected PMU/U8100 area and found no shorts, but also found PP3V8_AON_MPMU_ISNS_VIN missing (not shorted). Replaced U8100 just in case (have had them fail in weird ways), but no change.

Went back to inspecting CD3217 area because everything else seemed fine; I replaced them "just in case" to see if there would be *any* change at all, but there wasn't. Same exact behavior.

A bit lost here, as I've never had a missing-ppbus issue be anything other than things mentioned above, especially when it isn't shorted. The cycling of ppbus (between 1.9v and 0.9v) made me think there was a short on an auxiliary line, but I can't find anything amiss on any of the main rails. Have checked all caps for shorts to be sure.

Any help appreciated!

[mon2]

With no power, no battery, what is the exact resistance to ground on fuse F5200?

Attach the power adapter, measure the voltage to ground of:

I2C_SMC_PWR_1V8_SCL
I2C_SMC_PWR_1V8_SDA

I2C_SMC_PWR_3V3_SCL ; at the battery BMS connector
I2C_SMC_PWR_3V3_SDA

[ugamazing]

Thanks, Mon!

PPBUS diode is .478

I2C_SMC_PWR_1V8_SCL: 0v
I2C_SMC_PWR_1V8_SDA: 0v

I2C_SMC_PWR_3V3_SCL: 0v
I2C_SMC_PWR_3V3_SDA: 0v

[mon2]

PPBUS diode mode is ok and not shorted.

Test the following in diode mode (with no power to the board & no battery attached):

I2C_SMC_PWR_1V8_SCL
I2C_SMC_PWR_1V8_SDA

I2C_SMC_PWR_3V3_SCL
I2C_SMC_PWR_3V3_SDA

[ugamazing]

Thanks, Mon!

I2C_SMC_PWR_1V8_SCL .530
I2C_SMC_PWR_1V8_SDA .520

I2C_SMC_PWR_3V3_SCL .499
I2C_SMC_PWR_3V3_SDA .500

[mon2]

These lines are not shorted but you appear to be missing the pull-up voltages on each side of the level shifter. Can you confirm? The 1v8 and 3v3 rails are missing? They will be tied to the high side of the pull-up resistors on these SMBUS lines.

[ugamazing]

How are you concluding that specifically? The diode readings provided appear to match a working board; is it simply because the signals are missing that you've concluded this? Sorry if I'm confused in your question, lol.

[mon2]

SMBUS is an open-drain specification. That is, the SMBUS device / master can pull the line low but there is no high level. Instead, when a high signal is desired, the line is made to be open or floating. For this reason, you will see a local pull-up resistor to park the floating line to the high voltage. In the level shifter, one side is to 1v8 and the other to 3v3 if all is well.

So when the SMBUS lines are floating, the external voltages must be present else you will read 0v on these lines. The other possibility is that the bus master is pulling both lines low to 0v but do not think so.

Measure the voltage to ground on the pull-up resistors @ RD202 / RD203 and also RD200 / RD201.

RD200 ; should be 1V25 on pin # 1
RD201

RD202 ; should be 1V8 on pin # 1
RD203

RD207 ; should be 3v3 on pin # 1
RD208