Samsung S20 FE G780 Repair - Not Charging / Charges Slowly

🛠 Difficulty: 🟢🟡⚪️

⏰️ Repair time: 40 minutes.

Today a Samsung S20 FE came in for repair with a charging issue. It was charging very slowly — only about 0.3 amps.

When the phone was completely discharged, it wouldn’t start charging at all until the battery was “boosted” or partially charged directly using a special power supply.

We disassemble the phone and first check the D+ and D- lines - these often cause problems.

But here everything looks fine: no short circuit, and the resistance values are normal.

Just to be sure, we connect a different (known-good) sub-board for testing.

We remove the motherboard.

It’s unlikely that the problem is caused by the OVP (Over Voltage Protection) circuit, because in those cases charging doesn’t work at all, or there’s a short on the input line.

So we’ll start by replacing the power management IC - the MAX77705C.

This controller is commonly used in many Samsung smartphone models, including G970F / G973F / G975F / G980F / G985F / G988B / G991B.

Carefully cut out a small section of the metal shield to access the power controller.

Using a soldering station, we install a new controller and place the motherboard back in the housing for testing.

The tester now shows that when a regular charger is connected, the phone draws 1.2A.

We check the fast and super-fast charging modes - everything works properly.

After verifying the main phone functions, we can reassemble the device.