Battery Damage at J2

Thought for 31 sec

J2 is the speaker/output connector, not a battery input. It connects through ferrite beads directly to the NS4150B Class-D amplifier outputs: J2 pin 1 → FB1 → U2 VON, and J2 pin 2 → FB2 → U2 VoP.

If the tester connected a battery across J2:

Damage risk is moderate to high, especially if it was a Li-ion cell at ~3.7–4.2 V or higher.
There is no meaningful DC current limiting between J2 and the amplifier output pins; the ferrite beads are low-resistance at DC.
The NCF capacitors around J2 appear not fitted, so they likely did not absorb/protect much.
The most likely damaged part is U2, the NS4150B amplifier output stage. The ferrite beads could also be stressed, but U2 is the main concern.

Quick checks I’d do before powering normally again:

Measure resistance between J2 pins — look for a near-short.
Measure each J2 pin to GND and VCC with power off.
Power the board from a current-limited supply and watch for abnormal current.
If current is normal, test audio output at low volume first.
If output is dead, distorted, hot, or supply current is high, replace U2 first.

If it was only a very brief touch with a single Li-ion cell, it may have survived. If it was held connected, reversed repeatedly, or used a higher-voltage pack, I’d assume U2 is likely damaged.

Add protection and checks

Add J2 protection

Improve connector labeling

Run design checks

Create test procedure

C72

Capacitance

NC F

C74

Capacitance

NC F

C73

Capacitance

NC F

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