Lenovo a285 no power can't charge power button no response

[ss45]

Hi guys

I don't know how to solve this

Plugging USB c gave reading 19v in but battery not charging. Using other laptop battery charges just fine

With no battery and USB c adapter plugged in Vsys is around 9v. With battery only Vsys is equal to battery voltage. With battery and adapter plugged in Vsys is around 12v. So unlikely that bq 25700 is damaged nor the MOSFETs it controls

tps51285b supplies 3 and 5v. 3.3v present. 5v present if only enabled.

Closest schematic I could find is one for x270. In x270 3v enable and 5v enable are tight together, but in a285 they are not. So currently only 3.3v present (en around 2.7v), no 5v (en 0v)

Also in a285 the voltage controller for CPU is isl62771

No activity on bios cs pin, but 1.8v VCC present
I believe this is caused by amd integrated PCH in APU not getting v supply maybe ? Since the voltage controller isl62771 isn't getting 5v vcc which supplied by TPS ic mentioned above

3.3v on power button, pressing it pulls down the voltage
1.8v and 3.3v present on caps around thinkengine ic.

So that's it..... If anyone know where to check next

Thanks in advance

[mon2]

Re: Lenovo a285 no power can't charge power button no response

Hi. So BQ25700 is the charger IC ?

With the adapter & battery connected, measure the voltage on

pin # 19 (SRN)
pin # 20 (SRP)

BATDRV# pin # 21

SCL (pin #13)
SDA (pin #12)

CELL_BATPRESZ (pin # 18)


Post each reading.

[ss45]

Re: Lenovo a285 no power can't charge power button no response

Hi. So BQ25700 is the charger IC ?

With the adapter & battery connected, measure the voltage on

pin # 19 (SRN)
pin # 20 (SRP)

BATDRV# pin # 21

SCL (pin #13)
SDA (pin #12)

CELL_BATPRESZ (pin # 18)


Post each reading.

Hi. Here is the measurements

SCL sda 3.3v
Cell batpresz 3.459v
Sen srp 12.85v
Batdrv 13v

Vdda REGN 6V
Vbus 20
CHG ok 3.3

Upon plugging battery without ac adapter No activity on SCL SDA pin confirmed with oscilloscope

There is 1.8v and 3.3v at thinkengine ic tho

[mon2]

Re: Lenovo a285 no power can't charge power button no response

Review figure 40 of the above charger IC datasheet.

With no power, compare if you have a similar resistor based voltage divider on your logic board for the CELL_BATPRESZ pin.

With no power, check the resistance across the high side and low side resistors for this pin.

The posted voltage, from the datasheet, does not look correct.

What voltage do you see for CELL_BATPRESZ on the other laptop that is working?

If you charge this battery in the other laptop, does this battery work to power this logic that is not charging?

[ss45]

Re: Lenovo a285 no power can't charge power button no response

Review figure 40 of the above charger IC datasheet.

With no power, compare if you have a similar resistor based voltage divider on your logic board for the CELL_BATPRESZ pin.

With no power, check the resistance across the high side and low side resistors for this pin.

The posted voltage, from the datasheet, does not look correct.

What voltage do you see for CELL_BATPRESZ on the other laptop that is working?

If you charge this battery in the other laptop, does this battery work to power this logic that is not charging?

Well battery confirmed working. Sadly Currently no other laptop of similar model, previously there was, but already fixed and returned, different problem

Anyway the resistor 58.5 kohm to vdda 75.5 kohm to gnd
So the math checks out, ~3.4 is around 55% of 6v which according to the datasheet will configure the chip to charge 3s battery. The battery nominal voltage is 11.5 which also strengthen it is indeed 3s bat.

Hope is running thin, maybe dead mec (Lenovo superior) m

[tomodachi]

Re: Lenovo a285 no power can't charge power button no response

What is the current draw on ampermeter ?

by the way A285 appears to be same design with Thinkpad X280, hope it helps you

[ss45]

Re: Lenovo a285 no power can't charge power button no response

What is the current draw on ampermeter ?

by the way A285 appears to be same design with Thinkpad X280, hope it helps you

0.02 virtually 0 amp?

Yeah thanks for pointing that out.

[mon2]

Re: Lenovo a285 no power can't charge power button no response

by the way A285 appears to be same design with Thinkpad X280, hope it helps you

Excellent and many thanks !! Have the schematic in my database for this one.

See attached for the first DUAL MOSFET in a single package datasheet.

Remove all power. Meter in resistance mode.

Check the resistance between the following:

source & drain (review the datasheet on which pin is which on this package)
source & gate
gate & drain

post the readings for the 1st and then the 2nd mosfet inside this package.

[ss45]

Re: Lenovo a285 no power can't charge power button no response

All MOSFETs are fine, ie q1-q4, batfet all no short. Checked waveform on all gates, they are also fine and each conducts when proper signal is fed,

Acn aCP vbus around 19.9v
CHG ok around 3v if adapter is plugged in, 0v otherwise

The only suspicious thing is Output from nvdc system is around 9v without bat
Usually with nvdc it tries to match nominal cell voltage, right ?

Edit
Not necessarily, I have X1 carbon equipped with same ic, output without battery is around 10v, so....

That's it guys thanks for helping. I give up