Surface laptop 3 charging problem

[arashmoayyedizadeh]

Hello dear experts
I have a surface laptop 3 that doesnt charge the battery or turn on with adapter
Only turns on with battery
I was working on charging circuit and noticed that chgr_ok pinof bq25713 is fluctuating between 1.4 and 1.7 volts
It should be 1.8 volts because its pulled up to 1.8v by a 200k resistor
The strange thing is if i inject 1.8 volts or jump the pullup resistorfor a second it will start charging and works perfect
If i disconnect the charger and reconnect it i should inject or jump again
Any idea?
There is no other component there
Only charging ic , io and pullup resistor

[mon2]

Re: Surface laptop 3 charging problem

In general, do not jump or inject till more is known about the circuit and possible issues.

What is the history of the unit?

With care, measure the voltage of the pull-up side of the resistor that is mated to 1v8. What is the voltage? Is it a stable 1v8?

If not, that is of concern.

Next, remove all power. Meter in resistance mode. Measure the resistance to ground of this signal chgr_ok.

This signal is open-drain. This means the charger IC will be able to pull-down the signal but for a logic high ('1'); the line is open or floating. For this reason, the 200k resistor must be present to pull up this floating line to the soft logic high value.

If the pull-up voltage is stable @ 1v8 and this signal is fluctuating then the charger IC is believing the voltage in from the adapter is not stable or it is also fluctuating. Confirm if the adapter is suitable for this laptop. Confirm if this voltage is stable while attached to this laptop.