This is the circuit board for the USB connection to the speakers.

Inspect the five solder points for a broken wire connection. They are labeled SP-, M-, M+, R-, and R.

If any connections are broken, re-solder the wires. Use this image as a reference for correct wiring.

Carefully test the headset. Avoid touching the internals while the device is plugged in.

If your speaker is now working, skip to the conclusion.

Reinforcing the wires with electrical tape before reassembly is recommended.