NM-A901 Lenovo Yoga

[limxrich]

Hope someone can help.

Kinda confused about the power delivery of this unit. Instead of the normal 20V,, being delivered, only 5V is delivered to ADIN_1 in JP8, where the USB port board NS-A901 is connected. I used a USBC Tested connected in series, FYI.

Can someone explain how 20V or 5V is negotiated, and in this case, what circuit decides that? I was initially looking at PU3 (PMIC) but can't really understand where power is negotiated. Then looked at the SIO chip, however, how can the SIO chip negotiate if +3VALW_EC is not present. And saw that +3V_ALW is then produced by the the PU3 chip.

The USB3 DCIN board, the PU3, is quite an expensive gamble if replaced, while I have no idea how to program the SIO chip or even the thought of programming it is correct, given that the +3v power is non-existent.

I would really appreciate if someone could explain thoroughly.

Thanks!

MOD Edit: Link to schematic - https://www.badcaps.net/forum/showthread.php?t=81087
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[reformatt]

Re: NM-A901 Lenovo Yoga

Forget about 20V at this point since that comes a lot later in the sequence. The ISL9237 will run off the 5V initially, as it's a NVDC design (buck/boost converter). You should get at least 9V on Vin, which is needed to run the PMIC. If that is valid, this should produce +3PMIC to get the ball rolling for enables to +3VALW (which is needed to run the EC).

From the block diagram, USB-C power is via the Left IO board.

[limxrich]

Re: NM-A901 Lenovo Yoga

Forget about 20V at this point since that comes a lot later in the sequence. The ISL9237 will run off the 5V initially, as it's a NVDC design (buck/boost converter). You should get at least 9V on Vin, which is needed to run the PMIC. If that is valid, this should produce +3PMIC to get the ball rolling for enables to +3VALW (which is needed to run the EC).

From the block diagram, USB-C power is via the Left IO board.

Thanks for the input! 5V goes in to ISL9237 which then outputs 4.6V to PR57 and drain of PQ16, but no 9V is produced for Vin (0V). Looks like replacing ISL9237 is a good option, I guess? No shorts tested for the mosfets in the line.

[reformatt]

Re: NM-A901 Lenovo Yoga

Renesas charger IC troubleshooting is the same as TI BQ chips. Check for a short or low impedance on Vin, check first two MOSFETS PQ10/11, DCIN present on pin 17, ACDET (ACIN) > 0.8V etc. And obviously check U101/PQ15, PQ19, PQ20, PQ8.

ACOK dependant on +3VALW, which won't be there till you have some volts on Vin. If all that checks out, then change out the ISL.