EivoTech Laptop & Mobile Repair Master Course

Final Mobile Repair Technician Exam — Answer Key Part 3

Questions 81–120 Complete Answers

Section F — Display + Touch Continued

Question 81

Ghost touch sirf charging ke waqt hota hai. First comparison test kya hona chahiye?

Answer:

Sabse pehla test:

KNOWN-GOOD ORIGINAL / GOOD-QUALITY CHARGER + CABLE

use karke compare karo.

Reason:

Poor-quality charger electrical noise introduce kar sakta hai jo capacitive touch system ko disturb kare.

Diagnostic order:

Known-good charger
Known-good cable
Different power outlet/source
Screen/digitizer condition
Grounding/contact
Touch connector
Touch power filtering

Agar known-good charger ke saath ghost touch disappear:

Board touch IC ko first suspect nahi karna.

Golden Rule:

CHARGING-ONLY GHOST TOUCH → POWER SOURCE / NOISE FIRST

Question 82

MIPI high-speed lines par random long jumper kyun avoid karna chahiye?

Answer:

MIPI lines high-speed differential/signaling architecture use karti hain.

Unki performance depend karti hai:

Trace length
Impedance
Pair matching
Routing
Signal integrity

Random long jumper se:

Reflections
Data corruption
Display artifacts
Camera failure
Intermittent operation

ho sakti hai.

Rule:

HIGH-SPEED LINE KO NORMAL DC WIRE NAHI SAMJHNA

Gross open/short diagnose karo, lekin repair exact board design ke mutabiq honi chahiye.

Section G — Audio + Camera + Sensors

Question 83

Speaker diagnosis ka master formula likho.

Answer:

EXACT AUDIO FUNCTION → KNOWN-GOOD SPEAKER → CONNECTOR/PATH → AMP POWER → ENABLE → AUDIO BUS → AMP OUTPUT → SPEAKER

Simple version:

MODULE → POWER → CONTROL → DATA → OUTPUT

Question 84

Main speaker dead hai. Earpiece, mic aur Bluetooth audio normal. Known-good speaker same. Amp VIN/enable/audio bus good. Strong direction?

Answer:

Strong direction:

SPEAKER AMPLIFIER / AMP OUTPUT STAGE

Reason:

Known-good speaker ruled out
Amp power present
Enable present
Digital audio reaches amp
Other audio functions normal

Next check:

Amp output path
Connector/filter path
Amp itself

Diagnosis:

INPUTS GOOD + CONTROL GOOD + OUTPUT MISSING = OUTPUT/AMP STAGE STRONG SUSPECT

Question 85

Speaker output BTL/Class-D ho to scope safety ka important rule kya hai?

Answer:

Class-D/BTL speaker systems mein:

SPEAKER NEGATIVE TERMINAL GROUND NAHI HOTA

Normal earth-grounded oscilloscope ground clip ko speaker output terminal par blindly connect karna short create kar sakta hai.

Use:

Proper differential measurement technique
Suitable isolated/differential equipment
Manufacturer-recommended safe test point

Golden Rule:

BTL OUTPUT PAR GROUND CLIP BLINDLY MAT LAGAO

Question 86

Digital MEMS mic diagnosis ka formula likho.

Answer:

POWER → CLOCK → DATA → CODEC/SoC

Also inspect:

Mic module
Connector/path
Shared power
Clock/data lines

Question 87

One mic dead aur all mics dead mein diagnostic difference explain karo.

Answer:

One Mic Dead

Local fault stronger:

Specific mic
Local flex
Connector
Individual power/data path

All Mics Dead

Shared fault stronger:

Common power
Shared clock
Codec/SoC interface
Common audio control

Formula:

ONE FUNCTION DEAD = LOCAL FIRST

ALL RELATED FUNCTIONS DEAD = SHARED BLOCK FIRST

Question 88

Bottom mic charging sub-board par hai. Charging board replace karne ke baad call mic dead. First suspect?

Answer:

First suspect:

NEW CHARGING SUB-BOARD / MIC MODULE / CONNECTOR

Because fault immediately repair ke baad start hua.

Check:

Correct sub-board variant
Mic function
Board-to-board flex
Connector seating
Physical damage

Golden Rule:

FAULT AFTER REPAIR → TOUCHED / REPLACED AREA FIRST

Question 89

Camera master diagnostic formula likho.

Answer:

KNOWN-GOOD MODULE → POWER → RESET → CONTROL BUS → MCLK → HIGH-SPEED DATA → ISP/SoC

More specifically:

CAMERA → POWER → RESET → I2C → MCLK → MIPI CSI → ISP

Question 90

One rear camera dead hai, baqi cameras work. First diagnostic approach?

Answer:

Local subsystem first.

Order:

Known-good compatible camera
Connector inspection
Camera-specific power rails
Reset
I2C/control
MCLK
MIPI path later

Reason:

Baqi cameras working hone se shared camera system significantly prove hota hai.

Question 91

All cameras dead hain. Camera PMIC VIN present hai. All outputs missing hain. Enable/control absent. Root direction?

Answer:

Strong direction:

CAMERA PMIC ENABLE / UPSTREAM CONTROL PATH

Camera PMIC ko immediately replace nahi karna.

Because:

VIN good hai, lekin enable hi missing hai.

Trace:

Enable source
SoC/PMIC command
Pull-up/down
Control bus
Required power state

Rule:

VIN GOOD + EN MISSING = UPSTREAM CONTROL FIRST

Question 92

Camera power/reset/I2C good. MCLK missing. Kis stage ko diagnose karoge?

Answer:

Focus:

CAMERA MASTER CLOCK GENERATION / CLOCK ROUTING

Check conceptually:

MCLK source/control
Clock enable
Filter/path
Relevant safe test point

Camera module ko clock ke baghair proper image capture initialize karna mushkil ho sakta hai.

Question 93

Camera open karte hi phone restart karta hai. Known-good battery stable. Known-good camera fixes. Root cause?

Answer:

ORIGINAL CAMERA MODULE FAULT

Strong confirmation:

Original camera connected:

Restart.

Known-good camera:

Stable.

Possible original module:

Rail overload
Internal short/leakage
Bus fault

Lesson:

ISOLATION + KNOWN-GOOD REPLACEMENT = STRONG CONFIRMATION

Question 94

Camera after drop continuously shake karti hai. Known-good camera stable. Likely issue?

Answer:

Likely:

ORIGINAL CAMERA OIS / MECHANICAL CAMERA MODULE DAMAGE

Because known-good module solves issue.

Motherboard IC ko first suspect nahi karna.

Question 95

Sensor diagnosis ka master formula likho.

Answer:

POWER → RESET → CONTROL BUS → INTERRUPT → DATA/RESPONSE

For many sensors:

POWER → I2C/SPI → INTERRUPT → SoC

Question 96

Multiple sensors dead aur shared SDA stuck low. Ek sensor flex disconnect karne par bus normal. Root cause direction?

Answer:

Strong direction:

DISCONNECTED SENSOR / SENSOR FLEX PULLING SHARED BUS LOW

Because isolation se bus recover ho gayi.

Check:

Sensor module
Flex
Connector
Local ESD/protection

Question 97

Proximity sensor electrically good hai lekin screen replacement ke baad calls par screen wrong behave karti hai. Physical causes kya ho sakte hain?

Answer:

Possible physical causes:

Sensor alignment wrong
Sensor window blocked
Incorrect screen/frame
Adhesive blocking optical path
Dust
Missing/incorrect bracket
Wrong gasket
Protective layer interfering

Lesson:

SENSOR FAULT HAMESHA ELECTRICAL NAHI HOTA

Repair history important hai.

Section H — Wi-Fi + Bluetooth + GPS + NFC + Cellular

Question 98

Wi-Fi greyed aur weak Wi-Fi mein diagnostic difference explain karo.

Answer:

Wi-Fi Greyed / Unavailable

Feature initialize nahi ho rahi.

Focus:

DIGITAL SIDE

Power
Reset
Clock
Firmware
Digital bus
Combo IC later

Wi-Fi Available but Weak

System initialize ho chuka hai.

Focus:

RF / ANTENNA SIDE

Antenna contact
Coax
Filters
FEM
Matching network

Master Rule:

UNAVAILABLE = DIGITAL

AVAILABLE BUT WEAK = RF/ANTENNA

Question 99

Wi-Fi greyed + Bluetooth unavailable. First common blocks kaun se check karoge?

Answer:

Because Wi-Fi and Bluetooth commonly share combo subsystem:

Check:

Shared power rails
Reset
Reference clock
Digital communication path
Firmware/software
Combo IC only after prerequisites

Question 100

Wi-Fi ON hai but router sirf 1 meter ke andar milta hai. Strong direction?

Answer:

WI-FI RF / ANTENNA PATH

Check:

Antenna contact
Coax cable
Antenna module
RF filter/FEM
Physical frame/ground contact

Wi-Fi IC BGA first suspect nahi.

Question 101

2.4 GHz works but 5 GHz completely dead. Kis type ka fault possible hai?

Answer:

Strong possibility:

BAND-SPECIFIC RF PATH

Possible:

5 GHz filter
5 GHz FEM/LNA
Matching network
Antenna branch

Because shared digital Wi-Fi system works enough to operate 2.4 GHz.

Question 102

Wi-Fi/Bluetooth master formula likho.

Answer:

POWER → CLOCK → RESET → DIGITAL COMMUNICATION → RF FRONT-END → ANTENNA → FUNCTION

Question 103

GPS indoor test mein no lock. Kya GPS hardware fault conclude karoge?

Answer:

Nahi.

Indoor GPS/GNSS reception naturally weak ho sakti hai.

Correct first step:

OUTDOOR OPEN-SKY TEST

Known-good phone se same location compare karo.

Question 104

GPS proper outdoor test ka purpose kya hai?

Answer:

GNSS satellites se weak radio signals receive karta hai.

Buildings/roof/walls signal block ya attenuate kar sakte hain.

Outdoor test:

Better sky visibility
Fair known-good comparison
False diagnosis reduce

karta hai.

Question 105

GPS position correct hai but maps arrow wrong direction. GPS ya magnetometer?

Answer:

Strong direction:

MAGNETOMETER / COMPASS

GPS mainly position/movement provide karta hai.

Compass direction/orientation provide karta hai.

Question 106

NFC toggle works but tags detect nahi hote after back-cover repair. First inspect kya karoge?

Answer:

First:

NFC ANTENNA / REAR COIL / FLEX / CONTACTS

Because digital NFC controller likely initialize ho raha hai if feature available.

History points to rear assembly.

Question 107

NFC + wireless charging dono ek saath rear repair ke baad dead. Strong common cause?

Answer:

Strong common cause:

SHARED REAR COIL / FLEX / CONNECTOR ASSEMBLY

Many phones mein NFC aur wireless charging physically same rear assembly mein integrated ho sakte hain.

Question 108

No SIM aur No Service ka difference explain karo.

Answer:

No SIM

Phone SIM card/interface ko detect/read nahi kar raha.

Focus:

SIM SLOT / SIM INTERFACE

No Service

SIM detected hai but cellular network registration/signal nahi.

Focus:

MODEM / RF / ANTENNA / NETWORK

Question 109

No SIM master formula likho.

Answer:

KNOWN-GOOD SIM → SLOT → SIM VCC → RESET → CLOCK → DATA → MODEM

Question 110

SIM VCC, reset aur clock present. SIM data line abnormal low. Possible path?

Answer:

Focus:

SIM DATA LINE

Possible:

ESD/protection short
Filter fault
Connector contamination/damage
Trace fault
Modem-side issue later

Start from easiest/local protection path.

Question 111

SIM detected. Baseband info present. Manual network search mein operators nahi milte. Known-good phone same location mein operators find karta hai. Strong direction?

Answer:

Strong direction:

CELLULAR RECEIVE (RX) RF PATH

Check:

Antenna contacts
Coax
RF switch
Filters
LNA/FEM
Receiver/transceiver path later

Because modem is present and network environment is confirmed.

Question 112

Manual search operators find karta hai but phone register nahi karta. Receive ya transmit/account side? Explain.

Answer:

Manual search finding operators proves:

RECEIVE PATH WORKING SIGNIFICANTLY

Registration failure pushes direction toward:

SIM/account/carrier authorization
Transmit/TX path
Modem registration
Network compatibility

RX can still have imperfections, but it is no longer first suspect.

Question 113

Weak signal after frame replacement. First 4 physical checks kya honge?

Answer:

First physical checks:

Antenna spring contacts
Coax connectors/cables
Antenna flex/module
Frame grounding/antenna contacts

Also inspect:

Missing screws/contact brackets
Damage during frame change

Rule:

WEAK SIGNAL AFTER HOUSING WORK → PHYSICAL ANTENNA PATH FIRST

Question 114

Baseband/modem information itself missing hai. Antenna se pehle kis sequence ko check karoge?

Answer:

Digital baseband sequence:

POWER → CLOCK → RESET → FIRMWARE → COMMUNICATION

Check:

Baseband rails
Required reference clock
Reset
Firmware/system communication
Baseband IC/BGA only later

Antenna normally baseband information ko disappear nahi karti.

Question 115

IMEI/device identity ke repair mein professional security rule kya hai?

Answer:

ORIGINAL LEGITIMATE DEVICE IDENTITY PRESERVE KARO

Do not:

Clone
Spoof
Change identity for bypass
Copy another device's identifier

Repair ka goal original hardware/identity subsystem restore karna hai.

Question 116

4G works but 5G missing. Hardware se pehle kin 4 external conditions ko confirm karna hai?

Answer:

At least:

Device model/variant actually supports required 5G bands
SIM/carrier plan supports 5G
Area mein compatible 5G coverage
Software/network settings correct

Also:

Region variant
Carrier provisioning

Rule:

FEATURE SUPPORT + NETWORK CONDITIONS FIRST, BOARD REPAIR LATER

Section I — Battery Drain + Heating + Shutdown

Question 117

Battery drain master formula likho.

Answer:

KNOWN-GOOD BATTERY → SOFTWARE/LOAD → SLEEP STATE → WIRELESS COMPARISON → LEAKAGE/ACTIVE RAIL → ROOT CAUSE

More detailed:

BATTERY VERIFY → USAGE → SLEEP → AIRPLANE TEST → HEAT → RAIL → LOAD

Question 118

Standby drain aur active-use drain ka difference kya hai?

Answer:

Standby Drain

Phone idle/screen-off hone ke bawajood excessive power consume karta hai.

Possible:

Phone not sleeping
Background process
Network search
Hardware leakage

Active-Use Drain

High consumption only during normal heavy use:

Gaming
Camera
High brightness
Cellular activity

Some active drain can be normal.

Rule:

DRAIN KO PHONE STATE KE CONTEXT MEIN MEASURE KARO

Question 119

Battery 30% par phone off ho jata hai. First test?

Answer:

KNOWN-GOOD COMPATIBLE BATTERY

Because weak battery:

Software percentage show karne ke bawajood load par voltage sustain nahi kar sakti.

Then observe:

Load shutdown
Percentage stability
Charging behavior

Question 120

Battery health software 90% show karti hai lekin known-good battery se shutdown fix hota hai. Is se kya lesson milta hai?

Answer:

Important lesson:

SOFTWARE BATTERY HEALTH ESTIMATE FINAL HARDWARE PROOF NAHI

Battery may still suffer:

High internal resistance
Voltage sag under load
Intermittent internal fault

Known-good battery functional comparison stronger evidence hai.

Golden Rule:

BATTERY HEALTH NUMBER ≠ COMPLETE BATTERY CONDITION

Answer Key Part 3 — Questions 81–120 Complete ✅

Next — Answer Key Part 4

Questions 121–160 mein cover hoga:

Airplane-mode drain diagnosis
Hardware leakage
PMIC heat
Camera/call shutdown
Schematic + BoardView
Oscilloscope
First Falling Point
BGA
Sandwich board
Foldable phones
Dual batteries
Tablets
Final oral master questions

Uske baad Questions 1–160 ki complete theory answer key finish ho jayegi, aur phir 25 Final Advanced Practical Cases ki separate Answer Key bana sakte hain.