The switch sees the charger but does not charge

Hi guys! I am trying to repair a switch (hac-cpu-10) after a bad repair. The problem is the battery won’t charge. I installed a new M92T36 but it didn’t help. The console shows that the charger is connected (lightning icon), but not charging. All capacitors are good, I did not find a short circuit. The USB connector is visually intact.

I used the pinout from the M92T30 / 34/50, and this is what happens:
Pin6 VSVR - 3.3V
Pin5 VCCIN - 3.28V
Pin18 VDDIO - 1.8V
Pin36 VCONN_IN - 1.72V
Pin28 VEX - 0.75mV
Pin9 VB - 5.49V

What can I do? Perhaps we can advise me on other test points that will make it clear what is wrong.

I see that the BQ24 VBUS pin is only 64mV when the charger is connected.

It looks like one of the field-effect transistors is broken and is ringing in both directions.

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Which N-MOSFET is right?

I changed it to a pre-serviceable one, but the console still works in a strange way. The transistor does not open, and on pin1 of BQ24xxx is about 500 mV. Sometimes it opens and 5.4 volts appears on this pin, then the battery is charged. I still can’t figure out what the problem is.


THIS is the BQ Vbus trace, I believe you need to double check M92t


This is how I envisioned tracing. True, I have a variant of the CPU-10 board, and the transistors are slightly different. I marked the control circuit for this transistor. It’s embarrassing that charging works “from case to case.” Today it works, tomorrow it doesn’t, the day after tomorrow it works again.
I have four more spare chips, but I don’t have a soldering station, so I don’t want to risk overheating the board.

Fixed the same issue by replacing bq ic

A strange thing is happening. The console is now charging again. I measured the voltage at the gate of the transistor, and it is 11 volts. I have a non-original charger, it does not give out more than 5.4 volts, and now they go to the VBUS BQ. Slowly, but the charge goes.

Can anyone measure the gate voltage?