EivoTech Laptop & Mobile Repair Master Course

Final Mobile Repair Technician Exam — Answer Key Part 2

Questions 41–80 Complete Answers

Section C — No Power + PMIC Continued

Question 41

Standby rails good hain. Power-button press par power-key signal change nahi hota. Likely diagnostic block kaunsa hai?

Answer:

Strong direction:

POWER BUTTON / SIDE-KEY FLEX / PWR_KEY SIGNAL PATH

Check:

Physical button
Side-key flex
Connector
PWR_KEY line continuity/path
Pull-up/pull-down network
Relevant protection component

Agar known-good side-key flex se signal change start ho jaye:

Fault local flex/button side par confirm hota hai.

Question 42

Power-key signal correct change karta hai lekin startup rails appear nahi hoti. Kis stage ko investigate karoge?

Answer:

Ab power-button stage pass ho chuki hai.

Next direction:

PMIC STARTUP CONTROL / POWER-SEQUENCING STAGE

Check:

PMIC required inputs
Startup command/control
Required always-on supplies
PMIC communication/control where applicable
First expected startup rail

Formula:

PWR_KEY GOOD → START REQUEST → PMIC SEQUENCE → STARTUP RAILS

Question 43

Startup rails briefly appear aur phir disappear. Is case mein sabse important concept kya hai?

Answer:

FIRST FALLING POINT

Ye identify karo:

Kaunsi rail ya control signal sabse pehle collapse hoti hai?

Sequence:

Rail A

↓

Rail B

↓

Rail C

Agar Rail B pehle girti hai aur baqi uske baad:

Rail B/load/control direction stronger hoti hai.

Question 44

First Missing aur First Falling mein difference explain karo.

Answer:

First Missing

Startup sequence mein jo expected signal/rail kabhi appear hi nahi hui.

Example:

1.8V present.

1.2V present.

0.9V expected but absent.

Then:

0.9V = FIRST MISSING

First Falling

Rail initially appear hoti hai but cycling/restart mein sabse pehle collapse karti hai.

Example:

Rail A stable.

Rail B rises then collapses.

Uske baad Rail C off.

Then:

RAIL B = FIRST FALLING

Master Rule:

NO START = FIRST MISSING

CYCLING/RESTART = FIRST FALLING

Question 45

PMIC hot hai. Kya PMIC automatically faulty hai? Kam az kam 3 alternative explanations likho.

Answer:

Nahi.

Possible alternatives:

PMIC ka downstream output rail shorted hai.
External module excessive load le raha hai.
Main rail par another load problem hai.
Board boot repeatedly cycle kar raha hai.
PMIC normal power conversion ki wajah se warm ho raha ho.
Liquid leakage downstream excessive current cause kar rahi ho.

Golden Rule:

HOT PMIC = CLUE, PMIC FAULT PROOF NAHI

Section D — Boot Loop + RAM + Storage

Question 46

Logo-loop phone mein first 5 checks kya hone chahiye?

Answer:

Recommended first checks:

Known-good battery
Main power stability
Recovery/boot mode behavior
Recent history — update/drop/liquid/repair
Removable peripheral isolation where relevant

Then:

Firmware
Storage rails
RAM/storage deeper diagnosis

Question 47

Phone recovery mode mein stable hai lekin normal OS boot loop karta hai. Is se kya clues milte hain?

Answer:

Stable recovery suggests:

SoC significantly working
RAM significantly working
Storage at least partially accessible
Power system reasonably stable
USB/display functions may be working

Normal OS loop therefore pushes diagnosis toward:

Firmware/system partition
Driver
Peripheral initialization
Storage later-stage fault

Important:

Recovery stable hona full hardware-health proof nahi.

Question 48

Recovery mode bhi restart karta hai. Hardware suspicion kyun increase hoti hai?

Answer:

Recovery normal OS se simpler environment hota hai.

Agar recovery bhi unstable:

Software-only explanation weaker hoti hai.

Possible:

Battery/power instability
RAM
Storage hardware
Peripheral short/load
Thermal/hardware fault

Formula:

NORMAL OS + RECOVERY BOTH UNSTABLE → HARDWARE DIRECTION STRONGER

Question 49

UFS diagnosis ka master formula likho.

Answer:

POWER → RESET → CLOCK → HIGH-SPEED COMMUNICATION → RESPONSE

Then:

BOOT/FLASH BEHAVIOR

Question 50

UFS rail missing hai. Kya UFS chip bad conclude karoge?

Answer:

Nahi.

Missing UFS rail itself can prevent UFS from working.

Check:

Regulator VIN
Enable
Output rail resistance
Coil/bead/path
PMIC/control signal

Only after supply/control proven should UFS itself become suspect.

Question 51

UFS power/reset/clock correct hain. Official restore repeated same stage par fail hota hai. Cable/PC/software/power ruled out. Ab kis direction ka suspicion strong hota hai?

Answer:

PHYSICAL STORAGE / UFS HARDWARE / BGA PATH

stronger suspect banta hai.

Still major BGA work se pehle:

Board history
Connector/peripheral effects
Relevant storage signals
Data importance

consider karo.

Question 52

Ek flashing error aate hi UFS dead kehna wrong kyun hai?

Answer:

Flash error ki wajah ho sakti hai:

Bad cable
USB port
Computer issue
Wrong firmware
Power instability
Software tool issue
Connection drop

Isliye:

ONE FLASH ERROR ≠ UFS DEAD

Repeated reproducible evidence required.

Question 53

RAM fault aur storage fault symptoms overlap kyun kar sakte hain?

Answer:

Dono boot-chain ke critical parts hain.

If RAM fails:

Bootloader/kernel properly execute nahi kar sakta.

If storage fails:

Required boot code/data load nahi hoti.

Dono cause kar sakte hain:

No boot
Logo loop
Restart
Crash

Isliye power + boot-stage evidence needed.

Question 54

Boot loop sirf new camera module connect karne ke baad start hota hai. Camera disconnect karne se phone stable. Root-cause direction kya hai?

Answer:

Strong root direction:

CAMERA MODULE / CAMERA POWER OR BUS LOADING

Because isolation test ne direct relationship prove kar diya.

Camera module compatibility
Connector
Camera rail resistance
Shared I2C
Known-good camera

Question 55

Side-key power signal permanently active-low hai. Phone repeated restart karta hai. Kis part ko first isolate karoge?

Answer:

SIDE-KEY / POWER-BUTTON FLEX

Power removed state mein disconnect karke behavior compare karo.

Agar signal normal ho jaye:

Flex/button fault confirmed direction.

Section E — Charging System

Question 56

Charging system ka complete source-to-battery master formula likho.

Answer:

CHARGER → CABLE → PORT → DETECTION/CC → PROTECTION → CHARGER/POWER PATH → BATTERY

USB data separate path ho sakta hai:

PORT → ESD/FILTER → USB PHY/MUX → SoC

Question 57

No-charging phone par motherboard open karne se pehle kin external cheezon ko test karna hai?

Answer:

First:

Known-good charger
Known-good cable
Port physical inspection
Connector fit
Dirt/debris
Known-good battery where relevant

External-first testing unnecessary board work avoid karta hai.

Question 58

VBUS port par present hai. Protection IC ke input par present hai. Output absent. Downstream resistance normal. Diagnostic direction?

Answer:

Protection stage itself becomes strong suspect.

Because:

Input reaches it
Output should pass
Downstream not hard-short
Output absent

Still check:

Enable/control if applicable
Exact operating state

Question 59

Protection output absent hai aur downstream hard short hai. Protection IC ko faulty kehna kyun jaldi hoga?

Answer:

Protection IC may be doing its job:

BLOCKING A FAULTY DOWNSTREAM LOAD

Correct order:

Power remove
Downstream short verify
Net map
Root short find
Repair
Re-test protection path

Question 60

USB-C phone ek cable orientation mein charge karta hai aur doosri mein nahi. Strong suspect area kaunsa hai?

Answer:

CC1 / CC2 + USB-C PORT PATH

Check:

Port pins
CC1
CC2
ESD/protection
Connector solder/path

Question 61

CC1 aur CC2 ka purpose kya hai?

Answer:

USB-C Configuration Channel lines help with:

Cable orientation detection
Source/sink role detection
Basic current capability
Power-delivery communication framework

Simple concept:

CC LINES DEVICE KO BATATI HAIN KE USB-C CONNECTION KAISE ESTABLISH HUI HAI

Question 62

Normal charging works lekin fast charging nahi. Diagnostic order likho.

Answer:

Confirm device supports fast charging
Known-good compatible charger
Known-good compatible cable
Battery temperature/state
USB-C port condition
CC1/CC2 path
Negotiation/protocol support circuitry
Charger/power controller

Rule:

Normal charge working means complete charging system dead nahi.

Question 63

Charging icon aa raha hai lekin battery percentage increase nahi hoti. Kam az kam 5 possible reasons likho.

Answer:

Possible:

Weak charger
Bad/high-resistance cable
High system load
Weak battery
Battery temperature issue
Charging-path resistance
Charger/power IC issue
Battery communication/detection problem

Important:

ICON ≠ ACTUAL NET CHARGING GAIN

Question 64

Phone wired charging se dead hai lekin wireless charging works. Kis path ko diagnose karna chahiye?

Answer:

Wired charging-specific path:

USB SOURCE → PORT → CC/DETECTION → PROTECTION → WIRED CHARGING INPUT

Wireless charging working proves:

Battery and at least some downstream power-management parts are functional.

Question 65

Phone charge hota hai but PC detect nahi karta. Power path ya data path?

Answer:

USB DATA PATH

stronger suspect.

Because charging proves:

VBUS power path works significantly.

Check:

D+/D− or high-speed data path depending device
ESD/filter
USB mux/PHY
Port pins

Question 66

PC detect karta hai lekin battery charge nahi hoti. Kis subsystem ki direction strong hai?

Answer:

USB data path working significantly.

Focus:

CHARGING POWER PATH / CHARGER / BATTERY SIDE

Check:

VBUS power flow.

Protection.

Charger/power-path.

Battery detection.

Question 67

Battery temperature reading invalid hai. Charging par kya effect aa sakta hai?

Answer:

Phone may:

Refuse charging
Charge slowly
Disable fast charging
Show battery warning

Because charging controller needs safe battery temperature information.

Question 68

Damaged/swollen lithium battery ke saath technician ko kya karna chahiye?

Answer:

STOP NORMAL POWERED TESTING

Battery ko:

Puncture nahi
Compress nahi
Heat nahi
Open nahi
Direct-charge nahi

Use safe replacement/service procedure.

Question 69

Battery cell ko direct charge ya BMS bypass kyun nahi karna chahiye?

Answer:

Because lithium battery protection system manages:

Overcharge
Overcurrent
Temperature
Safe limits

Bypass/direct charging can create:

Overheating
Battery damage
Fire risk

Rule:

BATTERY MODULE KO REPAIR TEST OBJECT NAHI — SAFE COMPLETE MODULE SAMJHO

Question 70

Fast charging ko test karte hue manually higher USB-C PD voltage force karna wrong kyun hai?

Answer:

USB-C PD voltage normally device/source negotiation se select hoti hai.

Blindly higher voltage apply karna:

Protection bypass
Port damage
Charging IC damage
Board damage

cause kar sakta hai.

Use compatible supported charger/protocol only.

Section F — Display + Touch

Question 71

Black-screen phone ko no-power kehne se pehle boot kaise prove karoge?

Answer:

Check safe indicators:

Incoming call
Vibration/haptic
Notification sound
PC/USB detection
Recovery/service mode detection
Known-good display

If board responds:

No-power diagnosis wrong ho sakti hai.

Question 72

LCD aur OLED mein backlight difference explain karo.

Answer:

LCD

LCD pixels khud light emit nahi karte.

Separate:

BACKLIGHT SYSTEM

required hota hai.

OLED

OLED pixels self-emissive hote hain.

Traditional LCD-style backlight nahi hoti.

Question 73

LCD black hai but flashlight se faint image visible. Strong direction kya hai?

Answer:

BACKLIGHT PATH

Image/data path significantly working.

Check:

Backlight VIN
Driver
Enable/PWM
LED output/path

Question 74

LCD backlight master formula likho.

Answer:

BACKLIGHT INPUT → DRIVER → ENABLE/PWM → BOOST/OUTPUT → LED PATH

Question 75

OLED black screen ka master diagnostic flow likho.

Answer:

BOOT PROVE → KNOWN-GOOD OLED → CONNECTOR → PANEL POWER RAILS → RESET → MIPI/DATA

Remember:

OLED mein traditional backlight diagnosis nahi.

Question 76

Known-good display bhi black hai. Panel power missing. Next direction kya hai?

Answer:

DISPLAY POWER GENERATION/PATH

Check:

Display regulator VIN
Enable
Positive/negative bias where used
Filter/bead
Connector power pins

Not MIPI first.

Question 77

Display rails good hain. Reset stuck low hai. Kya MIPI ko first suspect karoge?

Answer:

Nahi.

Reset is earlier prerequisite.

First diagnose:

Reset source
Pull-up/down
Control IC/SoC command
Shorted reset line

Sequence:

POWER → RESET → DATA

Question 78

Vertical green line after drop. Known-good display perfect. Root cause?

Answer:

ORIGINAL DISPLAY / OLED PANEL DAMAGE

Known-good display isolation confirms motherboard path significantly okay.

Question 79

Touch completely dead. Image perfect. Known-good screen same fault. Touch power good. SDA stuck low. Screen disconnect karne ke baad SDA normal. Likely root-cause direction?

Answer:

If screen disconnect karne se SDA normal:

SCREEN/TOUCH MODULE IS PULLING BUS LOW

Strong suspect:

Touch panel/controller
Display flex
Connector-related module path

Motherboard shared bus is less likely because disconnect recovered it.

Question 80

Partial touch dead hone par digitizer/panel stronger suspect kyun hota hai?

Answer:

Touch controller communicate kar raha hota hai, lekin screen ke ek specific physical region ka sensing grid fail ho sakta hai.

Possible:

Digitizer trace damage
Panel internal damage
Flex damage

If entire bus/controller dead hota:

Often larger/full touch failure expected hota.

Practical Rule:

PARTIAL TOUCH = PANEL/DIGITIZER FIRST

especially after drop/screen damage.

Answer Key Part 2 — Questions 41–80 Complete ✅

Next — Answer Key Part 3

Questions 81–120 cover honge:

Ghost touch
MIPI
Audio
Microphones
Cameras
Sensors
Wi-Fi/Bluetooth
GPS
NFC
SIM/Baseband/RF
Battery drain
Random shutdown

Part 3 mein Question 81 se continue karenge.