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| HJX-112-DC Di-i11 V4.0 TWS charging board details showing the charging connector, 2R2 inductor, ZK406, SY3408 and battery circuit. |
HJX-112-DC / Di-i11 V4.0 TWS Charging Board Overview.
The HJX-112-DC / Di-i11 V4.0 is a compact charging and power-management board designed for TWS earbuds charging cases. Its job is to accept external USB power, charge the internal battery, and then distribute stored battery power to the left and right earbuds through the charging contacts.
The board contains a charging connector, a 2R2 power inductor, ZK406 charging IC, SY3408 earbuds charging IC, a mini switch, rechargeable battery connections, and supporting resistors and capacitors.
Because small TWS charging boards can have different PCB revisions, exact component functions should always be confirmed from the physical board, PCB traces, and measured voltages before replacing parts.
HJX-112-DC / Di-i11 V4.0 Component Overview.
The reported board information is:
Board Number: HJX-112-DC / Di-i11
Board Version: V4.0
Application: TWS Earbuds Charging Case
Charging Connector: USB Type-C or Micro-USB depending on board version
Power Bank Charging IC: ZK406
Earbuds Charging IC: SY3408
Power Inductor: 2R2
Battery: Reported 250mAh rechargeable cell
Control: Mini Push Switch
Supporting Components: Resistors and Capacitors
The circuit can be divided into three practical sections: input and battery charging, battery-to-earbuds power distribution, and control/stability components.
HJX-112-DC TWS Charging Circuit Working Principle.
The charging process starts when a USB charger is connected to the charging connector.
The external supply enters the PCB and reaches the charging and power-management section. The ZK406 is reported as the main power-bank charging IC responsible for managing the internal battery charging path.
The 2R2 inductor is part of the switching power stage and helps with voltage conversion and current regulation.
Once the internal battery stores energy, the SY3408 section supplies controlled power to the earbuds through their charging contacts.
A simplified power flow is:
USB Input → Charging Circuit → 2R2 Inductor / Power Stage → Internal Battery → SY3408 → Earbud Charging Contacts
The exact topology may vary by PCB revision, so the diagram above should be treated as a functional representation rather than a manufacturer schematic.
Charging Connector and Power Input.
The charging connector is the entry point for external power.
Depending on the board version, the connector may be USB Type-C or Micro-USB. The connector supplies the charging circuit with the external DC input required to charge the internal battery.
Charging Connector Repair Checks.
When the case does not charge, inspect the connector before testing the ICs.
A damaged connector can cause complete loss of charging even when the charging IC and battery are healthy.
Check for:
Broken or loose connector pins
Cracked solder joints
Damaged PCB pads
Corrosion
Missing 5V input
Short circuit on the input rail
A multimeter can be used to verify whether the expected charger voltage reaches the PCB after the connector.
2R2 Power Inductor.
The reported inductor marking is 2R2, corresponding to a nominal inductance of approximately 2.2µH.
The supplied specifications include:
Inductance: 2.2µH
Maximum DC Current: 4.1A
DC Resistance: 16.7mΩ
Tolerance: ±20%
Package: 0735
Construction: Shielded
Core: Ferrite
Operating Temperature: -40°C to +125°C
Reported Dimensions: 7.6 × 7.6 × 3.5mm
The original script does not provide a complete self-resonant-frequency value, so that parameter should not be assumed.
What the 2R2 Inductor Does.
The inductor is commonly used in a switching DC-DC converter or power-regulation stage.
It stores magnetic energy during switching and releases that energy in a controlled way as the switching circuit operates. This allows the power-management section to convert or regulate voltage efficiently.
The low DC resistance helps reduce conduction losses, while the shielded construction can help limit electromagnetic interference.
Inductor Repair Symptoms.
A damaged inductor can cause:
No battery charging
Unstable charging
Low or missing output voltage
Excessive heating
Intermittent power
Complete failure of the switching stage
Before replacing a 2R2 inductor, check whether the associated charging or switching IC has developed a short. Replacing only the inductor may not solve the original fault.
ZK406 Power Bank Charging IC.
The reported main battery charging IC is ZK406.
Its supplied information includes:
IC Number: ZK406
Serial/Marking: 1930
Pin Count: 6
This IC is described as the controller for charging the internal battery of the TWS charging case.
ZK406 Charging Function.
The charging IC receives power from the USB input and manages the battery charging process.
In a typical single-cell lithium battery charging arrangement, the charging system controls current and voltage according to the battery's charging requirements rather than applying the USB voltage directly to the cell.
The exact charging characteristics depend on the IC configuration and the supporting components used on the PCB.
The statement that ZK406 alone provides every battery protection function should not be assumed without the exact datasheet and schematic. Protection may also be provided by additional circuitry or a protected battery pack.
ZK406 Repair Guide.
When the charging case does not charge the battery, measure the circuit in stages.
First verify the USB input. Then check the charging IC supply and the surrounding components.
After that, check the battery connection and charging voltage.
If the input is present but the charging section produces no expected output, inspect the ZK406, its surrounding resistors and capacitors, the inductor, and possible short circuits.
SY3408 Earbuds Charging IC.
The reported earbud charging controller is SY3408.
The supplied board information lists:
IC Number: SY3408
Other Marking: 2150AD
Manufacturer Code: K3419B
Pin Count: 8
The function described for this IC is to manage power delivered to the charging contacts for the earbuds.
How the SY3408 Section Works.
After the internal battery has stored energy, the earbuds charging section distributes controlled power toward the left and right earbud contacts.
The IC and its surrounding circuit are responsible for controlling the charging path. The exact method used to detect a connected earbud and terminate or regulate charging depends on the design of the particular PCB.
This stage is important because the charging case must provide power to very small rechargeable batteries while maintaining appropriate electrical conditions.
SY3408 Repair Checks.
If the case battery is charged but the earbuds do not charge, inspect the SY3408 section rather than immediately replacing the battery.
Check the IC supply, charging-contact continuity, PCB traces, nearby passive components, and the charging contacts themselves.
Dirty or oxidised earbud contacts can also create a no-charge condition even when the charging board is functioning correctly.
Battery: 250mAh Rechargeable Cell.
The supplied information identifies a 250mAh battery and reports 4.2V.
For a single-cell lithium-ion or lithium-polymer system, 4.2V is commonly associated with the full-charge voltage rather than the nominal operating voltage. The actual battery label should therefore be checked before servicing or replacement.
Battery Function in the TWS Case.
The internal battery stores energy from the USB charging circuit.
When the case is disconnected from the charger, this stored energy is supplied to the earbuds through the power-management section.
Battery runtime depends on the actual cell capacity, battery condition, charging efficiency, earbud battery levels, conversion losses, and the number of charging cycles.
Battery Repair Checks.
A TWS charging case that shows no output may have a deeply discharged or degraded battery.
Measure the battery carefully and check the connector and solder joints.
A swollen, damaged, punctured, or unusually hot lithium battery should not be reused.
Never replace the cell with one having an unsuitable voltage, polarity, or charging specification.
Mini Switch and User Control.
The mini switch provides a physical user-control input.
Depending on the firmware and board design, it may be used for:
Power control
Battery status indication
Case reset
Wake-up or control functions
Pressing the switch sends a control signal into the logic or power-management section.
The exact behaviour depends on how the switch is connected to the PCB and controller, so it should not be assumed that every HJX-112-DC board uses it for the same function.
Mini Switch Repair.
If the charging case responds intermittently to the button, inspect the switch mechanically first.
Check for:
Worn switch contacts
Broken solder joints
Damaged PCB pads
Open signal trace
Incorrect pull-up or pull-down resistance
A simple continuity test can determine whether the switch is physically operating.
Resistors and Capacitors in the Charging Circuit.
Resistors and capacitors may be small, but they are essential to reliable operation.
Resistor Function.
Resistors can be used for current limiting, voltage division, signal biasing, feedback networks, pull-up or pull-down functions, and LED current control.
A failed resistor can change the operating conditions of an IC even when the IC itself is healthy.
Capacitor Function.
Capacitors store electrical energy and help stabilise supply rails.
In a TWS charging board, capacitors can reduce power-supply noise, support transient current requirements, and filter unwanted fluctuations around switching and charging circuits.
A shorted capacitor can cause a power rail to collapse, while an open or degraded capacitor can lead to unstable operation.
Problem and Solution: TWS Charging Board Repair.
Problem: TWS Case Does Not Charge.
First verify the USB charger and cable.
Then check the charging connector for mechanical damage and verify whether the input voltage reaches the PCB.
If the input is available, inspect the ZK406 charging section, 2R2 inductor, supporting components, and battery connection.
A missing charging output can be caused by a faulty charging IC, short circuit, damaged inductor, or failed battery.
Problem: Charging LED Does Not Turn On.
Do not assume the LED itself is the only problem.
First verify whether USB power reaches the board.
If the board is receiving power, inspect the LED, current-limiting resistor, charging-state signal, and related control circuitry.
Problem: Battery Charges but Earbuds Do Not Charge.
This symptom points toward the secondary charging section.
Check whether the battery has a reasonable voltage and whether the SY3408 receives its required supply.
Then inspect the charging contacts, PCB traces, and passive components around the earbud output stage.
Dirty spring contacts are another simple but common cause.
Problem: Only One Earbud Charges.
When one earbud charges and the other does not, the battery charging board may still be functioning.
Inspect the charging contacts and the corresponding PCB trace for the affected side.
A mechanical contact problem, damaged spring terminal, broken solder joint, or local component fault can isolate one charging path.
Problem: Charging Starts and Stops Repeatedly.
Intermittent charging can be caused by an unstable USB connection, damaged connector, poor battery connection, thermal protection, unstable power regulation, or a failing battery.
Measure the voltage while the charging process is active rather than checking it only when the board is idle.
Problem: 2R2 Inductor Becomes Hot.
An unusually hot inductor can indicate excessive current or a fault in the switching power stage.
Check for short circuits around the inductor and the charging IC.
Do not install a higher-current or physically different inductor simply because its rating appears larger. The inductance, saturation behaviour, resistance, package, and circuit requirements all matter.
Step-by-Step TWS Charging Board Troubleshooting.
For practical board repair, follow the power path instead of replacing components randomly.
Inspect the PCB for damage, corrosion, and burnt components.
Verify the USB input voltage.
Check the charging connector and its solder joints.
Measure the charging IC input.
Inspect the 2R2 inductor and surrounding switching components.
Check battery voltage and battery connections.
Verify the supply reaching the SY3408 section.
Inspect left and right charging contacts.
Check the mini switch and related control circuit.
Test resistors and capacitors around the faulty stage.
This method helps isolate the fault into the input section, battery charging section, power conversion stage, earbud charging section, or control circuit.
Key Circuit Reference.
| Section | Component | Reported Marking | Main Function |
|---|---|---|---|
| Input | Charging Connector | Type-C / Micro-USB | External power input |
| Power Conversion | Inductor | 2R2 / 2.2µH | Switching energy storage and voltage regulation |
| Battery Charging | Charging IC | ZK406 | Internal battery charging control |
| Earbud Charging | Charging IC | SY3408 | Earbud charging power management |
| Control | Mini Switch | — | User control or reset function |
| Power Storage | Battery | 250mAh, reported 4.2V | Stores energy for the case |
| Support | Resistors | Various | Current limiting, feedback and biasing |
| Support | Capacitors | Various | Filtering and power supply stabilisation |
Important Repair Precautions.
TWS charging boards work with lithium-based rechargeable batteries, so careless testing can create a serious safety risk.
Avoid shorting the battery terminals.
Do not apply an unknown voltage directly to the battery.
Use the correct charging input and verify polarity before applying external power.
When testing a board outside its original enclosure, keep conductive tools away from exposed battery and power terminals.
Note: Exact charging behavior can vary by PCB revision, so verify IC markings, battery specifications, and voltage readings on the actual HJX-112-DC / Di-i11 V4.0 board before repair.
Disclaimer: The component details in this guide are based on the supplied board information and general electronics principles; confirm the actual PCB circuit, component specifications, and battery ratings before modification or repair.
