Since you’ve already ruled out the cable and the computer, the issue is definitely within the MP3 player’s hardware, likely at the Micro-USB port or the data lines. Here is a step-by-step diagnostic flow:
1. Physical Inspection & Cleaning
Check inside the Micro-USB port with a magnifying glass and a bright light. Look for bent pins or debris. Clean the port using 90% Isopropyl Alcohol and a fine brush. Even a tiny piece of lint can prevent the data pins from making a proper connection.
2. Check for Cold Solder Joints (Reflow)
Open the device and inspect the 5 pins of the Micro-USB port where they meet the PCB. Because these ports take a lot of physical stress, the solder joints for Pin 2 (Data-) and Pin 3 (Data+) often crack.
- Action: Even if they look okay, it is best to reflow the pins with a fine-tip soldering iron and a bit of fresh flux.
3. Measure Data Line Voltages (Crucial Step)
While the device is plugged into a powered USB port, use a multimeter to measure the voltage on the Data lines (Pin 2 and Pin 3) relative to Ground (Pin 5).
- Expert Insight: You should typically see a small voltage (often between 2V to 3V) on these lines when the device attempts to 'handshake' with the computer.
- Analysis: If you see 0V on both data lines while power (5V) is present on Pin 1, there is either a break in the circuit traces or the main controller chip is not initiating the data transfer.
4. Continuity Test
Set your multimeter to Continuity mode (Beep). Test from the actual metal pin inside the USB port to a component further down the trace on the motherboard. This confirms that the signal is actually traveling from the connector into the circuit
crwdns2934105:0crwdne2934105:0
crwdns2934113:0crwdne2934113:0
crwdns2915270:0crwdne2915270:0
crwdns2889612:0crwdne2889612:0
0
2 
400 
1,5crwdns2936485:0crwdne2936485:0 