EivoTech Laptop & Mobile Repair Master Course
Mobile Repair Course — Part 25
Smartphone Audio + Mic + Speaker + Earpiece Advanced Fault Workflow
Chapter 25: Audio Fault ko “Speaker Kharab Hai” Kehne ke Bajaye Exact Audio Path Diagnose Karna
Smartphone audio system ek single circuit nahi hota.
Phone mein alag-alag audio functions ho sakte hain:
Main loudspeaker
Earpiece / receiver
Bottom microphone
Top microphone
Rear microphone
Noise-cancellation microphone
Headset/USB audio
Bluetooth audio
Isliye sabse pehla rule:
PEHLE EXACT AUDIO FUNCTION IDENTIFY KARO
Master formula:
EXACT AUDIO FUNCTION → MODULE → POWER → CONTROL/BUS → AMP/CODEC → OUTPUT
Microphone ke liye:
MIC → POWER/CLOCK → DATA → CODEC/SoC → SOFTWARE
1. Audio Fault ko Categories Mein Divide Karo
Customer complaint ko exact likho:
1. Main Speaker Dead
2. Earpiece Dead
3. Mic Dead
4. Low Volume
5. Distorted Sound
6. Crackling / Noise
7. Call Audio Dead
8. Recording Dead
9. Speaker Works but Earpiece Dead
10. Bluetooth Works but Internal Audio Dead
Ye classification diagnosis ko bohat narrow karti hai.
2. Speaker aur Earpiece Same Circuit Nahi
Phone ka:
Main bottom speaker
aur
Call earpiece
alag output paths use kar sakte hain.
Agar sirf ek dead hai:
Shared codec se pehle us specific output path ko check karo.
3. Audio Input vs Audio Output
Output
Speaker
Earpiece
Headphones
Input
Microphones
Diagnosis dono ki separate rakho.
4. Main Loudspeaker Basic Path
Simplified:
SoC / AUDIO CODEC → DIGITAL AUDIO BUS → SPEAKER AMP → SPEAKER
5. Earpiece Basic Path
Possible:
CODEC / AUDIO AMP → RECEIVER / EARPIECE
Exact design model-specific.
6. Microphone Basic Path
For digital MEMS mic:
MIC POWER → MIC CLOCK → MIC DATA → CODEC/SoC
7. Audio Codec Kya Hai?
Codec:
Coder / Decoder
Audio system mein ye analog/digital conversion aur audio routing perform kar sakta hai.
Modern phones mein codec:
Separate IC
PMIC/audio IC ke andar
SoC architecture ke saath integrated
ho sakta hai.
8. DAC
DAC:
Digital to Analog Converter
Digital audio ko analog signal mein convert karta hai.
9. ADC
ADC:
Analog to Digital Converter
Analog microphone signal ko digital form mein convert karta hai.
10. Digital Audio Phones
Modern phones mein bohat se microphones directly digital MEMS type hote hain.
Isliye traditional analog mic testing har phone par apply nahi hoti.
11. MEMS Microphone
MEMS:
Micro-Electro-Mechanical System
Very small microphone module.
Could contain internal electronics.
12. Multiple Microphones Kyun?
Phone multiple mics use karta hai for:
Voice calls
Video recording
Noise cancellation
Beamforming
Voice assistant
Camera recording
13. One Mic Dead vs All Mics Dead
One Mic Dead
Strong suspects:
Specific mic
Local power
Local data/clock
Sub-board
Connector
All Mics Dead
Strong suspects:
Shared clock
Shared power
Codec
SoC audio subsystem
Software
14. Main Speaker Dead Workflow
First:
Known-good speaker module.
↓
Contacts.
↓
Amp power.
↓
Amp enable/control.
↓
Digital audio bus.
↓
Amp output.
15. Known-Good Speaker
Before board repair:
Exact compatible known-good speaker test karo.
Speaker modules frequently fail due:
Liquid
Dust
Mechanical damage
Coil damage
16. Speaker Contact Pins
Many phones spring contacts use karte hain.
Check:
Bent contacts
Corrosion
Dirt
Missing pressure/contact
17. Speaker Mesh
Low volume ka simple reason:
Blocked speaker mesh.
Especially:
Dust.
Liquid residue.
Adhesive.
18. Low Volume ≠ Audio IC Fault
Always first check:
Speaker.
Mesh.
Housing seal.
Audio settings.
19. Speaker Resonance Chamber
Phone housing speaker acoustics ka part hoti hai.
Loose/missing gasket:
Sound weak/distorted kar sakta hai.
20. Speaker Amp
Main loudspeaker ko drive karne ke liye amplifier.
Modern phones:
Smart Amp / Class-D Amp
use kar sakte hain.
21. Smart Amp
Can monitor:
Speaker impedance
Temperature
Protection
Output load
depending design.
22. Amp Power Path
Master formula:
VIN → ENABLE → DIGITAL AUDIO → BOOST/OUTPUT → SPEAKER
23. Amp VIN Missing
Upstream power.
Do not replace amp first.
24. Amp Enable Missing
SoC/codec/control side.
25. VIN + Enable Good
Now check:
Digital audio activity.
26. Digital Audio Bus
Common interfaces:
I2S
TDM
SoundWire
PCM
Exact platform-specific.
27. I2S
Common digital audio interface.
May include:
Bit clock
Frame/word clock
Data
28. TDM
Time Division Multiplexing.
Multiple audio channels share digital bus.
29. SoundWire
Modern digital audio/control bus used in some smartphones.
30. PCM
Another digital audio communication concept.
Often used in voice/baseband contexts.
31. Digital Bus Present?
Scope can help check:
Clock/activity during audio playback.
If amp power good but no digital audio:
Amp may not be root cause.
32. Amp Output Safety
Important:
Modern Class-D speaker outputs often differential/BTL hote hain.
SPEAKER NEGATIVE TERMINAL KO GROUND ASSUME MAT KARO
33. BTL
BTL:
Bridge-Tied Load
Speaker ke dono terminals actively driven ho sakte hain.
34. Grounded Oscilloscope Warning
Grounded scope probe ka ground clip speaker output par lagane se:
Short create ho sakta hai.
Use proper differential/isolation measurement if required.
35. Multimeter on Speaker Output
Static DC reading alone audio output health prove nahi karti.
Audio is dynamic signal.
36. Speaker Amp Heating
Warm amp during loud playback can be normal.
Very abnormal heat + no audio:
Check load/amp rail.
37. Speaker Short
Speaker coil/module fault amp protection trigger kar sakta hai.
Known-good speaker first.
38. Amp Protection
Smart amp may shut output if:
Overcurrent
Thermal issue
Load abnormal
Protection ko bypass mat karo.
39. Earpiece / Receiver Fault
If loudspeaker works but earpiece dead:
Shared main audio system likely partially working.
Focus:
Receiver module
Contacts
Receiver-specific amp/path
Flex/connector
40. Known-Good Earpiece Test
First-line test.
41. Earpiece Low Volume
Common causes:
Dust
Mesh blockage
Liquid
Receiver weakness
Housing alignment
42. Earpiece Distortion
Possible:
Damaged receiver.
Moisture.
Loose fit.
Output-path issue.
43. Call Audio Routing
During phone call:
Audio may route differently depending:
Earpiece mode
Speakerphone mode
Bluetooth mode
Use this to isolate.
44. Call Works on Speakerphone but Not Earpiece
Strong direction:
Earpiece path.
45. Earpiece Works but Speakerphone Dead
Main speaker/amp path.
46. Bluetooth Audio Works
This proves:
Phone can generate/process audio at software/SoC level to a significant extent.
Internal output path becomes stronger suspect.
47. Bluetooth Audio Dead Too
Could be:
Software.
Audio service.
Codec/common system.
But classify carefully.
48. Headphones Work, Speaker Dead
Again speaker/amp path.
49. USB Audio Works, Internal Speaker Dead
Same idea.
50. Mic Fault Categories
Bottom Mic Dead
Top Mic Dead
Rear Mic Dead
All Mics Dead
Call Mic Dead but Recording Works
Recording Dead but Calls Work
Each gives different clue.
51. Voice Recorder Test
Very useful.
Test recording.
Then compare with call behavior.
52. Camera Video Mic Test
Front/rear camera recording may use different microphone combination.
Useful for locating specific mic fault.
53. Call Mic vs Video Mic
Do not assume same physical mic always used.
OEM may use different combinations.
54. Mic Location Mapping
Use service documentation/BoardView to identify exact microphone for:
Calls
Video
Noise cancellation
55. Bottom Mic on Sub-Board
Many Android phones bottom mic charging sub-board par hota hai.
If:
Charging port board recently changed
and mic dead:
Sub-board strong suspect.
56. Known-Good Sub-Board
Quickly isolates:
Mic/sub-board vs main board.
57. Mic Hole Blockage
Dust or adhesive:
Mic electrically healthy but sound low/muffled.
58. Mic Gasket
Correct acoustic seal matters.
Misaligned gasket:
Weak/muffled recording.
59. Digital MEMS Mic Power
Mic needs correct supply.
If missing:
No output.
60. Digital Mic Clock
Mic may need clock supplied from codec/SoC.
No clock:
No data.
61. Digital Mic Data
Mic outputs digital data stream.
Scope can show activity clue.
62. Mic Formula
POWER → CLOCK → DATA → SoC/CODEC
63. Mic Power Good + Clock Missing
Focus upstream audio control/clock.
64. Power + Clock Good + No Data
Possible:
Mic.
Signal path.
Connector.
65. Mic Data Present but No Recording
Then later:
SoC/audio routing/software
investigate.
66. Analog Mic
Some designs/accessories may use analog mic.
Path:
Mic bias
↓
Mic signal
↓
Codec ADC.
67. Mic Bias
Analog mic requires bias voltage.
Exact value model-specific.
68. Mic Bias Missing
Check codec/PMIC audio supply/control.
69. Noise Cancellation Mic
A secondary mic may help remove environmental noise.
If dead:
Calls may sound poor even if main mic works.
70. One Mic Failure Can Affect Call Quality
Symptoms:
Voice cuts
Voice sounds distant
Noise cancellation poor
71. All Mics Dead
Before codec replacement:
Check common:
Mic supply
Clock
Shared digital bus
Software
Flex/connector architecture
72. Audio Codec Power
Codec may have multiple rails:
Analog supply
Digital supply
I/O supply
Exact design-specific.
73. Codec Diagnosis Formula
POWER → RESET → CONTROL BUS → AUDIO CLOCK/BUS → RESPONSE
74. Codec Reset
If codec held reset:
Multiple audio functions can fail.
75. Codec Control Bus
Could be:
I2C.
SoundWire.
Other proprietary bus.
76. Shared Audio Failure
If:
Speaker + earpiece + all microphones
all dead:
Common codec/audio system becomes stronger.
77. But Software First?
If hardware measurements normal:
Software/audio service/settings may matter.
Don't replace codec solely on multiple symptoms.
78. Audio after Firmware Update
If fault immediately after update:
Test software/official firmware evidence before board work.
79. Audio after Drop
Physical first:
Speaker contact
Earpiece
Mic
Connector
Flex
Board crack
80. Audio after Liquid
Very common.
Check:
Speaker module
Mic
Mesh
Sub-board
Connector corrosion
Audio amp area
81. Water in Speaker
Can cause muffled/distorted sound.
Module may require replacement if physically damaged.
82. Liquid-Damaged MEMS Mic
Mic can fail internally.
Known-good module/sub-board comparison useful.
83. Corroded Audio Connector
Can create intermittent:
Speaker.
Mic.
Earpiece.
84. Audio after Screen Repair
Front earpiece/sensor flex may have been disturbed.
Check recent work first.
85. Audio after Charging Port Repair
Bottom mic often linked to same assembly.
86. Audio after Battery Repair
If unrelated audio fails after repair:
Inspect disturbed connectors/components before IC diagnosis.
87. Crackling Sound
Possible:
Damaged speaker
Poor contact
Amp instability
Audio data issue
Moisture
Known-good speaker first.
88. Distortion at High Volume Only
Could be:
Speaker damage
Poor housing/gasket
Amp/load
Battery/power stability
89. Distortion at All Volumes
Speaker/module first.
Then amp/data.
90. Speaker Very Quiet
Check:
Mesh
Speaker module
Acoustic chamber
Amp output limitation
91. No Sound but Vibrations Work
Haptic system separate.
Doesn't prove audio amp.
92. Haptic / Vibration Circuit
May involve:
Haptic driver
Vibration motor
SoC control
Separate from main audio.
93. Ringtone Silent but Media Works
Could be:
Settings
Software
Audio routing
Not hardware first.
94. Media Works but Calls Silent
Check call routing:
Earpiece.
Baseband/audio interface.
Software.
95. Calls Work but Media Silent
Main media speaker/output path.
96. One App Audio Dead
Likely software/app.
97. All Apps Speaker Dead
Hardware/system-level stronger.
98. Audio Codec vs Speaker Amp
Codec generates/routes audio.
Speaker amp provides power to speaker.
A dead speaker amp doesn't necessarily kill microphones.
99. Amp Failure Clue
Main speaker dead.
Earpiece and mics fine.
Amp supply/path strong direction.
100. Codec Failure Clue
Multiple audio input/output paths fail together.
But verify power/reset/bus first.
101. Power Rail Short in Audio Amp
Could cause:
No audio.
Restart.
Main rail load.
depending architecture.
102. Audio Amp on Main Battery Rail
Some high-power amps directly use battery-class supply.
Internal short can affect whole phone power.
103. Audio Fault Causing Restart
Phone stable until loudspeaker activated.
Then restart.
Check:
Speaker load
Amp
Amp supply
Battery stability
104. Restart at High Volume
Weak battery can mimic audio amp fault.
Known-good battery.
105. Mic Causes Boot Problem?
Some phones may depend on peripheral communication during boot.
But mic itself is not a default boot-loop diagnosis.
Need evidence.
106. I2C Audio Bus Stuck
If codec/control bus shared and stuck low:
Multiple devices can fail.
Use schematic and isolation where possible.
107. Digital Bus Testing with Scope
You can check activity presence.
But:
Activity ≠ correct data.
108. Logic Analyzer
Can help decode digital audio/control protocols if hardware supports them.
But not required for basic repair.
109. Audio Amp Enable Scope Test
Play audio.
Observe amp enable.
If enable never asserts:
Upstream routing/control.
110. Amp Enable Present but No Bus Activity
Audio source/control side.
111. Bus Activity Present but No Speaker Output
Known-good speaker tested?
If yes:
Amp/output stage stronger suspect.
112. Speaker Resistance
Standalone speaker coil resistance can be checked when disconnected, where appropriate.
But exact value varies by module.
Known-good comparison better.
113. Speaker Reads Open
If known-good should show finite coil path:
Open speaker could be faulty.
114. Speaker Reads Very Low
Could be abnormal short.
Compare same model.
115. Earpiece Resistance
Same principle.
Don't use universal ohm number.
116. MEMS Mic Resistance Testing
Digital MEMS mic ko simple resistance test se health prove nahi kar sakte.
Need power/clock/data/function.
117. Audio Diode Mode
Connector lines can be compared with known-good board.
Useful for:
Mic connector
Speaker control
Earpiece flex
118. Audio Connector Diode Abnormal
Could indicate:
ESD/filter/trace/component fault.
119. Audio Filter
Some mic/speaker control lines pass through filters.
Open filter can kill signal.
120. ESD Protection
External mic/headset/port circuits may use ESD devices.
Shorted ESD can pull signal low.
121. Headphone Jack Systems
Older phones may use 3.5mm jack.
Faults:
Headphone detect stuck
Audio routed away from speaker
Dirty jack
122. Stuck Headphone Mode
Phone thinks headset connected.
Internal speaker may be muted.
Physical detect/software path check.
123. USB-C Audio
Digital/analog accessory behavior depends model.
Port/data/CC configuration important.
124. Bluetooth Comparison Test
Very useful diagnostic:
Bluetooth sound good
Internal speaker bad.
→ Internal hardware path.
Bluetooth also bad
Software/common audio path possible.
125. Call Audio Comparison Matrix
Speakerphone good + earpiece bad
Earpiece path.
Earpiece good + speakerphone bad
Main speaker/amp.
Both outputs good but caller can't hear you
Mic path.
Bluetooth fully good while internal audio fails
Internal hardware strongly indicated.
126. Mic Comparison Matrix
Calls bad, voice recorder good
Call routing/specific mic possible.
Calls good, rear video bad
Rear/top mic specific.
All recording/calls bad
Common mic clock/power/audio system.
127. Case Study 1 — Main Speaker Dead
Known-good speaker tested.
Amp VIN good.
Amp enable good.
Digital audio activity missing.
Direction:
Upstream audio bus/control.
Not speaker amp first.
128. Case Study 2 — Speaker Amp Fault
Known-good speaker.
VIN good.
Enable good.
Digital audio activity present.
Amp output absent.
Direction:
Amp/output stage.
129. Case Study 3 — Low Speaker Volume
Board electrically normal.
Speaker mesh heavily blocked.
Root:
Physical acoustic blockage.
130. Case Study 4 — Distorted Speaker
Known-good replacement speaker sounds normal.
Root:
Speaker module.
131. Case Study 5 — Earpiece Dead
Main speaker works.
Known-good earpiece works.
Root:
Original receiver module.
132. Case Study 6 — Earpiece Still Dead
Known-good earpiece same.
Receiver power/path open at connector.
Direction:
Earpiece board path.
133. Case Study 7 — Bottom Mic Dead
Calls voice missing.
Rear video audio okay.
Known-good charging sub-board fixes.
Root:
Bottom mic/sub-board.
134. Case Study 8 — All Mics Dead
Mic power present.
Common mic clock missing.
Direction:
Audio clock/control.
135. Case Study 9 — One Digital Mic Dead
Power and clock present.
Mic data absent only on one mic.
Known-good mic/module works.
Root:
Mic.
136. Case Study 10 — Ghost Noise While Charging
Audio noisy only with poor charger.
Known-good charger fixes.
Direction:
External charger/noise/ground interaction.
137. Case Study 11 — Restart at High Volume
Phone reboots when speaker volume high.
Known-good speaker same.
Battery rail sags before reboot.
Known-good battery stable.
Root:
Battery.
138. Case Study 12 — Audio Dead After Water
Speaker and bottom mic fail.
Charging sub-board corrosion visible.
Known-good sub-board restores mic but speaker still dead.
Speaker module then tested faulty.
Lesson:
Liquid can create multiple audio faults.
139. Case Study 13 — No Call Audio Only
Media speaker works.
Voice recorder works.
Bluetooth call audio works.
Direction:
Call routing/baseband-audio path/software.
140. Case Study 14 — All Audio Dead After Previous Repair
Multiple audio rails missing.
Microscope finds missing tiny power-filter component near codec supply.
Root:
Common codec power path.
141. Case Study 15 — Crackling After Drop
Speaker contact spring bent.
Pressure changes sound.
Root:
Mechanical contact.
142. Main Speaker Diagnostic Worksheet
Phone Model: __________
Known-Good Speaker: __________
Speaker Contact: __________
Mesh/Housing: __________
Amp VIN: __________
Amp Enable: __________
Digital Audio Activity: __________
Amp Heating: __________
Output Evidence: __________
Final Direction: __________
143. Earpiece Worksheet
Known-Good Receiver: __________
Contacts: __________
Mesh: __________
Power/Path: __________
Main Speaker Works: __________
Bluetooth Works: __________
Final Direction: __________
144. Microphone Worksheet
Affected Mic: __________
Call Test: __________
Voice Recorder: __________
Front Video: __________
Rear Video: __________
Mic Power: __________
Mic Clock: __________
Mic Data: __________
Known-Good Module: __________
Sub-Board Tested: __________
Final Direction: __________
145. Codec Worksheet
Codec Power Rails: __________
Reset: __________
Control Bus: __________
Audio Clock: __________
Speaker Path: __________
Earpiece Path: __________
Mic Paths: __________
Bluetooth Comparison: __________
Final Direction: __________
146. Audio Fault Decision Tree
Exact function identified?
NO → classify first.
YES ↓
Known-good module tested?
NO → module first.
YES ↓
Physical contacts/mesh okay?
NO → repair physical.
YES ↓
Power present?
NO → power path.
YES ↓
Control/clock/bus present?
NO → upstream control.
YES ↓
Output still absent?
Amp/codec/load path.
147. Speaker Decision Tree
Known-good speaker?
↓
Amp VIN?
↓
Amp enable?
↓
Digital audio activity?
↓
Output stage?
148. Mic Decision Tree
Correct mic identified?
↓
Mic power?
↓
Clock?
↓
Data?
↓
Codec/SoC/software.
149. All Audio Dead Decision Tree
Software/routing check.
↓
Codec/common power.
↓
Reset.
↓
Control bus.
↓
Audio clock.
↓
Major IC conclusion last.
150. Low Volume Decision Tree
Mesh blocked?
↓
Known-good speaker/earpiece.
↓
Housing/gasket.
↓
Amp/output limitation.
151. Distortion Decision Tree
Known-good module.
↓
Contact/housing.
↓
Power stability.
↓
Amp/data.
152. Audio Restart Decision Tree
Trigger specific to loud audio?
YES ↓
Known-good speaker.
↓
Battery stable?
↓
Amp supply stable?
↓
Amp/load.
153. Common Beginner Mistake 1
No sound = speaker IC bad.
154. Common Beginner Mistake 2
Known-good speaker test skip karna.
155. Common Beginner Mistake 3
Blocked mesh ko motherboard fault samajhna.
156. Common Beginner Mistake 4
All microphones ko same physical mic samajhna.
157. Common Beginner Mistake 5
Digital MEMS mic ko simple continuity se diagnose karna.
158. Common Beginner Mistake 6
Speaker negative terminal ko ground samajhna.
159. Common Beginner Mistake 7
Grounded scope directly Class-D/BTL speaker output par lagana.
160. Common Beginner Mistake 8
Amp warm = amp faulty.
161. Common Beginner Mistake 9
Bluetooth comparison use na karna.
162. Common Beginner Mistake 10
Codec ko major fault bolna before power/reset/bus verification.
163. Speaker Golden Rules
1. Known-good speaker first.
2. Mesh aur contacts inspect karo.
3. Amp diagnosis = VIN → Enable → Audio Bus → Output.
4. Class-D/BTL output ko ground referenced mat samjho.
5. Restart at high volume mein battery bhi test karo.
164. Microphone Golden Rules
1. Exact mic identify karo.
2. One mic dead aur all mics dead separate diagnosis hain.
3. Digital mic = Power → Clock → Data.
4. Sub-board mic fault common ho sakta hai.
5. Mic hole/gasket acoustic system ka part hai.
165. Codec Golden Rules
1. Codec ko common audio controller samjho, magic speaker IC nahi.
2. Power → Reset → Control Bus → Audio Bus follow karo.
3. Multiple audio faults common codec path ko point kar sakte hain.
4. Software/routing evidence ko ignore mat karo.
5. Major codec replacement last-stage evidence-based decision ho.
166. Part 25 Quick Revision
Audio Codec
Audio conversion/routing/control system.
DAC
Digital to analog conversion.
ADC
Analog to digital conversion.
MEMS Mic
Tiny integrated microphone technology.
Smart Amp
Speaker amplifier with control/protection features.
Class-D
Efficient switching audio amplifier.
BTL
Speaker ke dono terminals actively driven.
I2S
Digital audio interface.
TDM
Multiple channels sharing timed bus.
SoundWire
Digital audio/control bus.
167. Part 25 ka Sabse Important Lesson
Audio repair mein “sound nahi aa rahi” enough diagnosis nahi.
Pehle exact function identify karo:
SPEAKER?
EARPIECE?
MIC?
CALL AUDIO?
RECORDING?
Phir comparison karo:
INTERNAL AUDIO vs BLUETOOTH
Speaker ke liye:
MODULE → AMP POWER → ENABLE → AUDIO BUS → OUTPUT
Mic ke liye:
POWER → CLOCK → DATA → CODEC/SoC
Aur agar main speaker dead hai lekin:
Earpiece works
Mics work
Bluetooth works
to poore codec ko blame karna logical nahi.
Sabse important safety rule:
CLASS-D / BTL SPEAKER OUTPUT KA KOI BHI TERMINAL AUTOMATICALLY GROUND NAHI HOTA.
Professional audio repair ka rule:
EXACT AUDIO PATH DHOONDO — “AUDIO IC” KO DEFAULT ANSWER MAT BANAO.
Mobile Repair Course — Part 25 Complete
Next — Mobile Part 26: Smartphone Camera + Sensor Advanced Fault Diagnostic Workflow
Part 26 mein hum Part 10 ko real repair workflow mein convert karenge:
One camera dead
All cameras dead
Black camera preview
Camera app crash
Camera shake
Autofocus fault
OIS fault
Flash not working
Front/rear camera switching problem
Camera power rails
Camera PMIC
Reset
I2C
MCLK
MIPI CSI
Shared camera bus
Proximity/ALS
Gyroscope/accelerometer
Compass
Hall sensor
Sensor-related boot/restart faults
Master formula:
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