 |
| OnePlus Bullets Z2 E305A circuit details with BES2300 Bluetooth IC, SGM41513 charging section, battery and practical repair information. |
OnePlus Bullets Wireless Z2 E305A Circuit Details and Repair Guide.
The OnePlus Bullets Wireless Z2 is a popular Bluetooth neckband designed around a compact audio and power-management circuit. For repair technicians, identifying the main board, Bluetooth processor, charging section, battery circuit, crystal oscillator, microphone, control switch, and audio driver section can make troubleshooting much easier.
This guide focuses on the E305A board reference mentioned in the supplied repair data and explains how the major sections work together. It also separates board-level repair information from specifications officially published by OnePlus, because component markings and internal board revisions can differ between production batches.
According to OnePlus, the Bullets Wireless Z2 uses Bluetooth 5.0, a 12.4 mm driver, USB Type-C charging, a 220 mAh battery, up to 30 hours of playback at 50% volume, and a Bluetooth connection range of up to 10 meters. OnePlus also specifies 5V charging and a 10-minute charge for up to 20 hours of playback under its stated test conditions.
OnePlus Bullets Wireless Z2 E305A Board Information.
Model and board identification.
The repair reference supplied for this device identifies the model as OnePlus Bullets Z2 and the model number as E305A.
The reported board information is:
Model: OnePlus Bullets Z2
Model Number: E305A
Board Number: BTE326 / BTE-326
Board Version: 3.1
Bluetooth IC: BES2300
Reported Bluetooth IC Code: 24311049
Manufacture Code: F435321H
Crystal Reference: 26.000 MHz
These markings are useful when comparing a damaged PCB with a replacement board or when locating the correct circuit section during repair. Board markings should always be checked directly on the physical PCB before replacing components, because similar-looking boards can use different revisions or component values.
Main Circuit Architecture of the E305A Board.
The internal circuit can be viewed as several connected sections rather than one single circuit.
The USB Type-C input feeds the charging and protection stage. The charging section manages the lithium-polymer battery. Battery power is then distributed to the Bluetooth/audio processing section and other low-power circuits.
The Bluetooth processor acts as the central control and communication unit. It receives wireless audio data, processes the audio path, communicates with the microphone and control switch, and sends the processed signal toward the audio output stage.
A simplified signal flow can be understood as:
USB Type-C → Charging/Protection Section → Battery → Power Management → Bluetooth Processor → Audio Output / Microphone / Control Interface
This architecture is important during repair because a fault in one section can create symptoms that appear to come from another section.
Bluetooth Section and BES2300 Processor.
BES2300 Bluetooth IC.
The supplied board reference identifies the BES2300 as the main Bluetooth CPU or audio processor.
This section is responsible for the wireless communication path and a large part of the audio-processing workload. In practical repair work, problems around this section can appear as Bluetooth pairing failure, unstable connection, audio dropouts, no sound, abnormal current consumption, or complete loss of power if the processor's supply rail is missing.
The supplied circuit information associates the Bluetooth section with Bluetooth 5.0, a 2.4 GHz operating band, an approximately 10-meter connection range, and a 26 MHz crystal reference.
OnePlus officially specifies Bluetooth 5.0 and a connection range of up to 10 meters for the Bullets Wireless Z2.
26 MHz crystal oscillator.
The 26.000 MHz crystal is used as a timing reference for the Bluetooth system.
A crystal oscillator is important because wireless communication and digital audio processing require accurate timing. A damaged crystal, poor solder joint, shorted capacitor around the oscillator circuit, or missing oscillator supply can prevent the Bluetooth system from starting correctly.
When a device appears completely dead after the battery and charging section have been confirmed good, the oscillator area should be inspected carefully before assuming that the main Bluetooth IC itself has failed.
Audio Driver Section.
12.4 mm speaker drivers.
The Bullets Wireless Z2 uses 12.4 mm audio drivers. OnePlus officially lists the driver size as 12.4 mm and specifies a frequency response of 20 Hz to 20 kHz on its product information.
The driver section converts the electrical audio signal into sound. In the circuit, the audio path ultimately reaches the two speaker units through their respective connections.
If only one side has no sound, the fault may be caused by a damaged driver, broken wire, cracked solder joint, connector issue, or PCB trace rather than a failure of the Bluetooth processor.
Before replacing an IC, technicians should therefore check continuity from the audio output section to the driver connection.
Microphone and Control Switch Section.
SH-031 microphone.
The supplied repair data identifies an SH-031 microphone in the audio input section.
The microphone is used for voice capture during calls and voice-related functions. Its signal is handled by the main audio and Bluetooth processing circuitry.
A microphone fault may be caused by contamination, physical damage, a broken PCB trace, an open connection, or a problem in the microphone bias and signal path.
For a no-microphone complaint, checking the microphone itself first is normally more practical than immediately replacing the Bluetooth processor.
Four-pin mini switch.
The board is also described as using a four-pin mini switch for user controls.
Depending on the circuit implementation, button commands can be used for functions such as play/pause, track control, call handling, or other programmed operations.
A defective switch can create symptoms such as random commands, missing button response, or a control that permanently appears pressed.
A multimeter continuity test can help determine whether the switch contacts change state correctly when pressed.
Battery and Charging Circuit.
Battery specifications.
The supplied repair script identifies a BLE871 lithium-polymer battery with these board-reference markings:
Battery Model: BLE871
Battery Type: Lithium Polymer
Battery Code: 1ICP4/10/39
Reported Capacity: 129 mAh
Reported Energy Rating: 0.496 Wh
Nominal Voltage: 3.85 V
Full-Charge Voltage: 4.4 V
However, there is an important specification difference to keep in mind. OnePlus's official Bullets Wireless Z2 product information lists a 220 mAh battery for the retail product.
Therefore, the 129 mAh battery information should be treated as a specific board or battery reference from the supplied repair material rather than a universally confirmed specification for every Bullets Wireless Z2 unit.
This distinction matters during battery replacement. The safest approach is to match the original battery's physical dimensions, chemistry, nominal voltage, protection arrangement, connector or solder configuration, and PCB requirements rather than choosing a battery based only on capacity.
SGM41513 Power and Charging IC.
Charging IC reference.
The supplied board-level information identifies the SGM41513 as the main charging or power-management IC.
The reported markings are:
IC: SGM41513
Code: YTQF24
Manufacture Code: N21HC
In a repair context, this section is especially important when the neckband does not charge, draws abnormal current, shows no charging indication, or repeatedly disconnects from the charger.
The charging stage controls the electrical conditions required to charge the battery safely. A fault around this section can also affect the battery supply available to the Bluetooth processor.
CC/CV charging behaviour.
Lithium batteries are generally charged using controlled charging stages. The charging circuit regulates current during the earlier charging phase and manages voltage as the battery approaches its maximum charging level.
This is why a device should not be repaired by directly connecting a battery to a USB supply. The charging control circuitry is part of the battery safety system.
Thermal and protection functions.
The supplied repair information also associates the power-management section with protection against abnormal charging conditions, temperature problems, excessive voltage, and short circuits.
In practical repair work, these protections should not be bypassed. A temporary bypass can make a damaged board appear operational while creating a much greater battery or PCB safety risk.
USB Type-C Charging Section.
Charging connector.
The OnePlus Bullets Wireless Z2 officially uses a USB Type-C charging port. OnePlus also specifies a 5V charging input and states that its fast-charging performance is based on controlled test conditions.
The supplied repair notes describe a Type-C connector compatible in physical form with connectors used in some other mobile devices.
The connector itself is a common failure point because the neckband is frequently carried, bent, plugged in, and unplugged.
Typical physical problems include:
Broken or loose USB Type-C pins
Cracked solder joints
Damaged connector housing
Shorted power pins
Corroded charging contacts
Broken PCB traces near the connector
A connector should not be replaced solely because the device is not charging. First confirm whether the fault is actually at the USB input, protection stage, charging IC, battery, or system power rail.
D4 Diode and Charging Protection.
The supplied circuit information identifies a component marked D4 near the charging section.
A diode in this area can be part of the input or protection network, depending on the exact PCB design.
For repair purposes, the important point is that a shorted or open protection component can interrupt the charging path or create abnormal current behaviour.
Before replacing D4, compare its diode-mode readings with a known-good board or verify the circuit position and component specification. Replacing a protection diode with an arbitrary diode can alter the protection characteristics and may damage the charging circuit.
OnePlus Bullets Wireless Z2 E305A Circuit Repair Guide.
Problem: Neckband does not power on.
Start with the battery rather than the main Bluetooth IC.
Measure the battery voltage directly at the correct battery terminals. A lithium-polymer battery with an unexpectedly low voltage may indicate deep discharge, battery failure, or a protection circuit issue.
Next, inspect the USB Type-C connector and check whether the charging circuit receives the expected input.
If the battery has a reasonable voltage but the device remains completely dead, continue toward the power-management and system-supply rails.
The next checks should include:
Battery voltage
USB input voltage
Charging IC area
Protection components
Battery-to-PCB connection
Main power rails
Visible PCB damage
Corrosion or liquid contamination
Problem: No charging current.
First inspect the Type-C connector for mechanical damage.
If the connector is physically sound, verify that the input supply reaches the charging circuit. A damaged connector solder joint, broken trace, shorted diode, failed charging IC, or battery problem can all prevent normal charging.
The stated repair reference mentions approximately 5V input and charging current in the range of roughly 0.2A to 0.4A under its described conditions, while OnePlus officially documents 5V charging and fast-charge performance under specific laboratory conditions.
Charging current should not be used as a universal fixed value because the actual current changes with battery state, temperature, charger behaviour, protection circuitry, and load conditions.
Problem: Charging symbol appears, but battery level does not increase.
This situation often points to a battery-side or charging-control problem.
Check whether the battery voltage rises during charging. If the input side is correct but the battery voltage remains unchanged, inspect the charging IC, battery connection, protection path, and PCB traces.
A battery with increased internal resistance may also charge poorly or discharge immediately after the charger is removed.
Problem: Battery drains very quickly.
Fast battery drain can come from several causes.
A damaged battery is one possibility, but abnormal current consumption from the Bluetooth processor, a shorted capacitor, moisture damage, or another faulty component can create the same symptom.
A useful repair technique is to compare standby current with that of a known-good board. If the board consumes unusually high current while no audio is playing, locate the section that is becoming warmer or drawing excessive current before replacing the main IC.
The official product specification of up to 30 hours is based on OnePlus laboratory testing at 50% volume, so real-world battery life naturally varies with volume, wireless conditions, functions, software, and usage habits.
Problem: Bluetooth does not connect.
Inspect the Bluetooth section around the BES2300 and 26 MHz crystal reference.
Check the main power supply to the Bluetooth processor first. A processor that is not receiving a stable supply cannot establish a wireless connection.
Then inspect:
Crystal area
Crystal capacitors
Solder joints around the processor
Antenna or RF connection area
PCB damage
Corrosion
Previous repair work
If the board powers on normally but repeatedly loses connection, do not immediately conclude that the BES2300 is defective. Power instability, clock problems, RF damage, or mechanical PCB damage can produce similar symptoms.
Problem: One side has no audio.
Start at the affected driver.
Check the speaker resistance and the physical wire connection. Then inspect the solder joints and trace continuity between the audio output section and the driver.
If the driver itself is healthy, follow the signal path back toward the audio-processing section.
This method is safer and faster than changing the Bluetooth processor without evidence.
Problem: Both sides have no audio.
When Bluetooth pairing and button controls work correctly but there is no sound, inspect the audio supply and signal path.
Possible causes include an audio output-stage problem, disconnected driver wiring, damaged PCB traces, or a board-level power issue affecting the audio circuitry.
A known-good audio source can also help determine whether the problem is digital pairing related or located after the Bluetooth connection has already been established.
Problem: Microphone does not work.
Inspect the SH-031 microphone and its solder joints first.
Look for contamination, physical cracks, broken traces, or missing bias voltage where applicable.
When the microphone is electrically healthy but still produces no input, follow the signal path toward the Bluetooth/audio processor.
Problem: Buttons are not responding.
For a four-pin mini switch, test the switch with a multimeter.
The contact state should change predictably when the button is pressed. If it remains permanently open or permanently closed, the switch may be defective.
If the switch is working correctly, inspect the PCB trace and the processor input path.
Practical E305A Board Repair Workflow.
A structured repair sequence reduces unnecessary component replacement.
Step 1: Visual inspection.
Check the entire PCB under magnification.
Look for:
Liquid or corrosion
Burn marks
Missing components
Cracked solder joints
Broken traces
Damaged USB Type-C connector
Battery wire damage
Previous soldering work
Step 2: Check the battery.
Measure the battery before connecting unnecessary external power.
Do not force-charge an unknown or physically swollen lithium battery.
Step 3: Check USB input.
Confirm that the charging connector and input path are receiving the expected supply.
Step 4: Check protection and charging circuitry.
Inspect the D4 area and the charging IC section for shorts, open components, and damaged traces.
Step 5: Check system power rails.
If charging appears normal but the board does not boot, check whether stable voltage is reaching the Bluetooth/audio processing section.
Step 6: Check the 26 MHz crystal area.
For a no-boot or no-Bluetooth condition, inspect the oscillator network and its surrounding components.
Step 7: Test audio and microphone paths.
Once the processor and power system are confirmed operational, check the driver, microphone, switch, and associated PCB traces.
This sequence helps isolate the actual failure instead of replacing expensive ICs unnecessarily.
Important Circuit Repair Precautions.
The E305A board is a small, densely packed electronic assembly. Excessive heat can damage pads, flexible connections, microphones, nearby capacitors, or the main Bluetooth processor.
Battery-related repair deserves additional caution because lithium-polymer cells can become dangerous when punctured, overheated, shorted, or incorrectly charged.
Do not bypass charging protection to force a battery to charge.
Do not install an unverified charging IC or diode simply because the package looks identical.
Always compare the original component marking, PCB position, circuit function, and measurements before replacement.
Verified OnePlus Bullets Wireless Z2 Specifications.
For reference, OnePlus officially lists the Bullets Wireless Z2 with a 12.4 mm driver, Bluetooth 5.0, up to 10 meters of Bluetooth range, USB Type-C charging, a 220 mAh battery, up to 30 hours of battery life at 50% volume, and 10 minutes of charging for up to 20 hours of playback under the stated test conditions.
OnePlus also lists 20 Hz–20 kHz as the frequency response range. This corrects the “20 kHz” wording found in the supplied script, which is incomplete as a frequency-response specification.
The exact BES2300, SGM41513, BLE871, D4, and BTE326 markings discussed above should be treated as board-level repair references from the supplied E305A information and should be confirmed against the actual PCB before component replacement.
Note: This guide is intended for technical reference and board-level troubleshooting; always verify component markings, measurements, and PCB revision on the actual E305A board before carrying out a repair.
Disclaimer: The board-level IC numbers, component codes, battery markings, and repair observations in this article are based on the supplied repair reference and may vary by board revision or production batch. Official product specifications have been cross-checked with OnePlus, but internal circuit details should be verified from the physical PCB and reliable service documentation before replacement or modification. Lithium-polymer battery and mains/USB charging repairs should be performed with appropriate safety precautions.
