PILOT RUN ISSUE LOG

Product: TWS Charging Case (Model TC-100)
Pilot Run Date: September 8-10, 2026
Pilot Run Quantity: 200 units
Location: Production Line 3, [Factory Name]
Document Owner: Li Wei, Production Engineer
Contributors: Zhang Ming (Quality), Chen Hao (R&D), Wang Lei (Line Supervisor)

Issue Log Overview

Critical Issue #1 – Line Stopped

Logged by: Wang Lei (Line Supervisor)
Time: September 8, 2026, 10:42 AM
Status: Resolved

Description:
Line stopped at Station 7 (hall switch calibration). The hall switch was not triggering consistently. 12 out of 30 units failed the lid-open detection test. The lid-open detection is used to wake the earbuds when the case is opened. Failure means the earbuds do not wake up.

Investigation:
Chen Hao (R&D) inspected the failed units. The hall switch is a magnetic sensor. It detects the magnet in the lid. When the lid is closed, the magnet is near the sensor. When the lid is open, the magnet moves away. The sensor triggers.

The issue was the magnet position. The magnet is glued into the lid. The glue thickness varies. In some units, the magnet is 0.5mm further from the sensor than in others. The sensor sensitivity threshold is not being met.

Root Cause:
Magnet positioning tolerance is too loose. The glue dispenser is not calibrated. The magnet position varies by ±0.8mm. The sensor requires ±0.3mm.

Fix:

1. Calibrate the glue dispenser. (Completed September 8, 2:00 PM)

2. Add a fixture to hold the magnet in position during curing. (Implemented September 9)

3. Add a 100% hall switch functional test at Station 7. (Implemented September 9)

Verification:
After the fix, 50 consecutive units passed the hall switch test. The line resumed at 3:30 PM on September 8.

Responsible: Chen Hao (R&D), Wang Lei (Line Supervisor)
Closed: September 9, 2026

Major Issue #2 – Wireless Charging Intermittent

Logged by: Zhang Ming (Quality)
Time: September 8, 2026, 3:15 PM
Status: Resolved

Description:
Wireless charging test at Station 12 showed intermittent charging. 8 out of 50 units failed to initiate charging on the first attempt. The units would charge after repositioning on the charging pad.

Investigation:
The wireless charging coil is mounted on the bottom of the case. The coil is aligned with the charging pad. The alignment tolerance is ±1.5mm. If the case is placed slightly off-center, the charging does not initiate.

The issue was the coil position. The coil is held in place by a plastic bracket. The bracket was not fully seated in some units. The coil was tilted by 2-3 degrees. The tilt reduced the coupling efficiency.

Root Cause:
Bracket seating issue. The bracket is press-fit. The press-fit force is not controlled. Some brackets are not fully seated.

Fix:

1. Add a visual inspection step to confirm bracket seating. (Implemented September 9)

2. Add a fixture to press the bracket into position with controlled force. (Implemented September 10)

3. Increase the wireless charging test time from 5 seconds to 10 seconds. (Implemented September 10)

Verification:
After the fix, 100 consecutive units passed the wireless charging test on the first attempt.

Responsible: Li Wei (Production), Zhang Ming (Quality)
Closed: September 10, 2026

Major Issue #3 – Battery Connector Loose

Logged by: Li Wei (Production)
Time: September 9, 2026, 9:30 AM
Status: Resolved

Description:
Battery connector at Station 4 showed intermittent contact. 5 out of 50 units failed the battery voltage test. The voltage reading fluctuated.

Investigation:
The battery connector is a pogo pin connector. The pogo pins contact the battery terminals. The pins are spring-loaded. The issue was the spring tension. The springs were not compressed enough. The contact was intermittent.

The spring tension is specified at 0.5N ± 0.1N. The incoming inspection records showed that the springs were within specification. But the connector housing was slightly out of tolerance. The housing depth was 0.15mm too deep. The extra depth reduced the spring compression by 0.15mm. The reduced compression reduced the contact force.

Root Cause:
Connector housing tolerance issue. The housing supplier's tolerance was too loose. The housing depth varies by ±0.2mm. The specification is ±0.05mm.

Fix:

1. Reject the current housing batch. (Completed September 9)

2. Require the housing supplier to tighten the tolerance. (Implemented September 10)

3. Add a 100% battery voltage test with a 5-second load test. (Implemented September 10)

Verification:
After replacing the housing batch, 100 consecutive units passed the battery voltage test.

Responsible: Li Wei (Production), Chen Hao (R&D)
Closed: September 10, 2026

Major Issue #4 – Lid Open/Close Detection False Trigger

Logged by: Zhang Ming (Quality)
Time: September 9, 2026, 2:00 PM
Status: Resolved

Description:
Hall switch false trigger at Station 8. The hall switch triggers when it should not. The lid is closed but the sensor detects "open." The earbuds wake up when they should not.

Investigation:
The hall switch is a magnetic sensor. The magnet is in the lid. The sensor is in the case. The sensor detects the magnetic field. The magnetic field strength varies with temperature. The hall switch threshold is fixed. At high temperature, the magnetic field strength decreases. The sensor may not detect the magnet.

But the issue was not temperature. The issue was the magnet polarity. The magnet is a disc magnet. The polarity is not marked. The magnet can be installed with either polarity facing the sensor. One polarity works. The other polarity does not. 5% of the magnets were installed with the wrong polarity.

Root Cause:
Magnet polarity not controlled. The magnet is symmetrical. The installer cannot tell which side is which. The polarity is random.

Fix:

1. Mark the magnet with a colored dot to indicate polarity. (Implemented September 9)

2. Add a visual inspection step to confirm polarity. (Implemented September 9)

3. Add a functional test at Station 8 to verify hall switch operation. (Implemented September 10)

Verification:
After the fix, 100 consecutive units passed the hall switch test.

Responsible: Wang Lei (Line Supervisor), Chen Hao (R&D)
Closed: September 10, 2026

Minor Issue #5 – Cosmetic Scratch on Case

Logged by: Zhang Ming (Quality)
Time: September 8, 2026, 11:20 AM
Status: Open

Description:
Cosmetic scratches on the outer case. 12 out of 100 units have visible scratches on the top surface. The scratches are fine but visible under light.

Investigation:
The scratches are caused by the handling process. The cases are placed in a bin after molding. The bin is plastic. The cases rub against each other. The rubbing causes scratches.

Root Cause:
Inadequate protection during handling. The cases are not separated. They are in a common bin.

Proposed Fix:

1. Add separators to the bin. (Proposed September 9)

2. Use soft foam liners in the bin. (Proposed September 9)

3. Add a visual inspection step after molding. (Proposed September 10)

Status: Pending approval from production manager.

Responsible: Wang Lei (Line Supervisor)

Minor Issue #6 – LED Indicator Brightness Variation

Logged by: Li Wei (Production)
Time: September 9, 2026, 10:15 AM
Status: Open

Description:
LED indicator brightness varies between units. Some LEDs are bright. Some are dim. The variation is visible when units are side by side.

Investigation:
The LEDs are sourced from a single supplier. The LED forward voltage varies by ±0.15V. The LED driver circuit uses a fixed resistor. The current varies with forward voltage. The brightness varies.

Root Cause:
LED forward voltage tolerance too wide. The specification is ±0.1V. The supplier's actual variation is ±0.15V.

Proposed Fix:

1. Require the LED supplier to tighten forward voltage tolerance. (Proposed September 10)

2. Add a binning step to sort LEDs by forward voltage. (Proposed September 10)

3. Use a constant-current LED driver instead of a fixed resistor. (Proposed September 10)

Status: Pending R&D review.

Responsible: Chen Hao (R&D)

Minor Issue #7 – Case Lid Alignment

Logged by: Wang Lei (Line Supervisor)
Time: September 9, 2026, 3:45 PM
Status: Resolved

Description:
Case lid does not align flush with the case body. The gap on one side is 0.3mm. The gap on the other side is 0.8mm. The lid appears tilted.

Investigation:
The lid hinge is a plastic living hinge. The hinge is molded with the case. The hinge thickness varies. The hinge is thinner on one side. The thin side flexes more. The lid tilts.

Root Cause:
Mold wear. The hinge cavity in the mold is worn. The hinge thickness is not uniform.

Fix:

1. Repair the mold. (Completed September 10)

2. Add a lid alignment check at Station 3. (Implemented September 10)

Verification:
After mold repair, 50 consecutive units passed the lid alignment check.

Responsible: Wang Lei (Line Supervisor)
Closed: September 10, 2026

Summary of Pilot Run Findings

Critical Issues Resolved: 1 of 1
Major Issues Resolved: 3 of 3
Minor Issues Resolved: 12 of 43
Minor Issues Open: 31 of 43

Most Significant Finding:
The hall switch issues (critical and major) were both caused by magnet positioning and polarity. Both issues were resolved with process controls and fixtures. The design was not changed.

Second Most Significant Finding:
The wireless charging intermittent failure was caused by a bracket seating issue. The fix required a fixture and a longer test time. The design was not changed.

Third Most Significant Finding:
The battery connector loose issue was caused by a housing tolerance problem. The fix required a new housing batch and a tightened tolerance. The design was not changed.

Observation:
Most of the pilot run issues were process-related, not design-related. The design is sound. The production process needs improvement.

Next Steps:

1. Complete the remaining minor issues before the next production run. (Target: September 20)

2. Update the process control plan with the fixes implemented during the pilot run. (Target: September 15)

3. Schedule a second pilot run for 500 units. (Target: September 25)

4. Review all open minor issues with the production manager. (Target: September 20)

Prepared By:
Li Wei, Production Engineer
September 11, 2026

Reviewed By:
Chen Hao, R&D Engineer
September 11, 2026

Approved By:
Zhang Ming, Quality Manager
September 11, 2026

This log is for internal use only. Distribution to third parties is prohibited without the written consent of the Quality Department.

Pilot run notes from the production floor. The issues nobody told you about. The one that stopped the line. And the fix

47 issues logged during the pilot run. 3 critical. 1 stopped the line. Production floor notes from a TWS charging case pilot run. Real issues, real fixes.

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