Hello everyone. After repairing dozens of TWS Bluetooth earbud PCBs, I’ve summarized several common issues with on-board Flash programming and their solutions to help fellow enthusiasts avoid these pitfalls:
1. The Main Controller Circuit Causes the Flash to Be Unrecognized
Issue: The CS pin of the on-board Flash is pulled low by the main controller, preventing the programmer from putting the chip into read mode.
Solution: Use a jumper wire to connect the Flash’s CS pin directly to VCC, temporarily disconnecting it from the main controller. Reestablish the connection after reading is complete.
2. PCB trace interference causing read error checksums
Issue: The
earbud PCB has limited space, and SCK/SIO traces cross the antenna and power layers, causing signal interference
Solution: Use shielded probe cables; during reading, position the antenna section of the earbud PCB away from the programmer, or add a 104 filter capacitor to the Flash power supply pin
3. On-board power circuit pulls down the supply voltage
Issue: The headphone’s lithium-ion battery power circuit pulls down the 3.3V supply provided by the programmer to the Flash, causing unstable reading
Solution: Disconnect the headphone’s battery ribbon cable during programming to have the programmer supply power directly to the Flash, or use an external independent 3.3V auxiliary power supply
4. Poor contact with mini-package Flash probes
Issue: The pin pitch of WLCSP/QFN-packaged Flash is extremely small, making it difficult for standard probes to make stable contact
Solution: Use a dedicated probe holder with a positioning fixture, or secure the PCB with high-temperature tape to ensure even probe pressure
5. Encrypted Flash cannot be read directly
Issue: Some headphone brands have Flash memory with built-in encrypted firmware; attempting to read it directly results in garbled data
Solution: In this case, data can only be read via the main controller’s ISP interface or using the original manufacturer’s dedicated programmer; generic programmers cannot read it directly
Translated with DeepL.com (free version)
