Lenovo Flex not charging

[koby058]

Hi people!

The board is LC57-IAU MB 213062 -1M.

Here is High res board picture, i could not find a schematic

what i have:

the board is working on battery, without battery type c remains on 5v with battery it is changing to 20v (0A pulled by board), but it powers on.

charging IC was replaced with same results.

attached pictures of what i have so far and also the PD controller

can you please help me understand why no charging ?

[mon2]

Hi. Same PU4401 appears on other Flex 5 schematics so they can be used for reference to debug.

[koby058]

Thanks mon2 for you reply, in this schematic it looks like a bq25710 chip not southchip

Also, how would you suggest me to continue the debug?

Is thee a post/video that explains how main power rail is created in this kind of circuit ?

[Sametbey]

The charging circuit whose measurements I recorded before. It may help.

[koby058]

I can see that on pin4 CHRG_OK is missing, also on the left dual mosfet i see 12.5v or 5v when no battery, what is changing the voltage to 12.5v from 20v?

Can any one advise?

[mon2]

Attached. If PWR_CHG_ACOK = 0v then review this circuit and also if the mosfet is open or closed @ PQ4404. It appears to be enabled so this is pulling the PWR_CHG_ACOK line to 0v.

Short answer is that, the gate voltage should be 0v or ground from the EC. Only if the gate is OFF = 0v, then you will have a voltage @ PWR_CHG_ACOK.

[koby058]

The gate is shorted to ground,
I am not sure i understand you on this line:
Short answer is that, the gate voltage should be 0v or ground from the EC. Only if the gate is OFF = 0v, then you will have a voltage @ PWR_CHG_ACOK.

[mon2]

This mosfet is disabled. If the mosfet is off, there must be a voltage at the circled point. Confirm the voltage on each side of resistor @ PR4432.

[koby058]

I cannot find it, i measure the one on the attached pic (red dot)
left side 0.4v right side 0v
I can also see that on the charger IC pin7 vdda looks shorted with only 1.6ohms

[mon2]

We have different boards for this Flex 5. Let check others.

[mon2]

PQ4404 on my shared partial schematic is most likely not the same PQ4404 on yours unless we can confirm the wiring back to the charger IC. For my shared schematic, the PWR_CHG_ACOK pin is linked to this mosfet.

[mon2]

Attached is what may be a similar datasheet for the part on your board.

Manufacturer: Southchip (my first time hearing of this company out of China).

[koby058]

so i found that the charger ic was shorted, i have replaced it again and now i have charging light but still not charging
on pin 22 i can see that i have batt voltage

ican see that batdev is 0

can yoo advise on how i can continue here ?

[koby058]

CHRG_OK is 2.8v and i understand it must be 3.3, is this correct ?

pin detail from chip schematic

Open drain active high output. CHRG_OK outputs logic high indicating VBUS is in the range of 3.5V
to 24V and no fault occurs

[jadao]

Attached is what may be a similar datasheet for the part on your board.

Manufacturer: Southchip (my first time hearing of this company out of China).

Hello, just to let you know the chip SOUTHCHIP SC8885L found in a NM-E211 rev 1.0 board (Lenovo Thinkpad E14 Gen 4) was perfectly replaced by a BQ25710, The boardview and schematics show a BQ25710 but the reality on the board is a southchip SC8885L. All surrounding component and their values were exactly as per the schematic.

So i gave a try and it worked perfect, it seems to be an equivalent.
Datasheet for BQ25710 is available, for southchip SC8885L I only found SC8885C.

The original southchip on the board suffered from liquid damage, its internal LDO on the REGN pin 28 was 5.1V instead of 6V.

I hope this may help someone.

[mon2]

jadao, awesome find!! Thanks for sharing.

[koby058]

Thanks for your reply
i have replaced the two switching mosfets and now i get charging light but the board pulling 0.3-0.5A fluctuating
but now i hear clicking sound from the mosfets /chatger IC area, i have tried another SC8885L and i am getting the noises as well
I only have BQ25700A in stock and i cannot believe the customer will wait for an order
do you think it can come instead of BQ25710 ?
Any other suggestion ?

[mon2]

I would be concerned with the mv step resolution as shown in the following comparison chart:

https://e2e.ti.com/support/power-man...with-a-bq25700