EivoTech Laptop & Mobile Repair Master Course

Final Mobile Repair Technician Exam — Answer Key Part 1

Questions 1–40 Complete Answers

Section A — Smartphone Architecture

Question 1

Smartphone motherboard ka complete basic power-to-boot sequence likho.

Answer:

Basic sequence:

BATTERY → MAIN POWER RAIL → PMIC → STANDBY/ALWAYS-ON RAILS → POWER REQUEST → STARTUP RAILS → SoC → CLOCK + RESET → RAM → STORAGE → BOOTLOADER → OS

Simplified:

Battery main power provide karti hai.
Main battery rail PMIC tak jati hai.
PMIC always-on rails generate karta hai.
Power-key/start request receive hota hai.
PMIC startup rails sequence mein enable karta hai.
SoC power receive karta hai.
Required clocks active hote hain.
Reset release hota hai.
RAM initialize hoti hai.
SoC storage se boot data read karta hai.
Bootloader run hota hai.
Kernel/OS load hota hai.
Display, network, audio aur baqi peripherals initialize hote hain.

Master Formula:

POWER → CLOCK → RESET → RAM → STORAGE → EXECUTION

Question 2

PMIC ka main role kya hai? Minimum 5 functions likho.

Answer:

PMIC:

Power Management Integrated Circuit

Main functions:

Main battery/input power receive karna.
Different voltage rails generate karna.
Rails ko correct sequence mein ON/OFF karna.
Always-on/standby power provide karna.
SoC, RAM, storage aur peripherals ko supply dena.
Power-key/startup requests handle karna.
Power-state transitions manage karna.
Protection/thermal monitoring mein role.
Kuch designs mein reset/power-good coordination.
Dynamic voltage scaling support karna.

Golden Rule:

PMIC ka matlab sirf:

“3V/5V banana”

nahi.

Ye complete power-sequencing system ka central part hai.

Question 3

SoC aur simple CPU mein kya difference hai?

Answer:

CPU primarily instructions execute karta hai.

SoC:

System on Chip

ek single chip mein bohat se subsystems integrate karta hai.

SoC ke andar ho sakta hai:

CPU
GPU
Memory controller
ISP
NPU
Display engine
USB controllers
Security engine
Modem-related logic
Audio/DSP blocks

Isliye smartphone mein “CPU” bolne par practically aksar SoC ki baat ho rahi hoti hai.

Question 4

Modern SoC ke andar kam az kam 6 major blocks ke naam likho.

Answer:

Examples:

CPU cores
GPU
Memory controller
ISP — Image Signal Processor
NPU/AI accelerator
Display engine
DSP
USB controller/PHY
Security engine
Modem/baseband-related subsystem on integrated platforms

6 likhna enough tha, lekin technician ko overall architecture samajhni chahiye.

Question 5

CPU/SoC boot karne ke liye basic 5 requirements kya hain?

Answer:

Core master requirements:

POWER → CLOCK → RESET → RAM → STORAGE

Power

Required SoC rails present.

Clock

Timing/reference clocks present.

Reset

SoC reset state se release.

RAM

Working memory initialize.

Storage

Boot firmware/data accessible.

In mein se koi critical stage fail:

Boot stop ho sakta hai.

Question 6

RAM aur UFS/eMMC/NAND ka difference explain karo.

Answer:

RAM

Temporary working memory.

Phone ON hone ke waqt:

OS
Apps
Active data

temporarily RAM mein process hota hai.

Power OFF:

RAM data normally retain nahi karti.

UFS/eMMC/NAND

Permanent/non-volatile storage.

Ismein:

Bootloader
OS
Apps
User data

store hota hai.

Power OFF ke baad bhi data rehta hai.

Simple Formula:

RAM = WORKING MEMORY

STORAGE = PERMANENT DATA

Question 7

Boot ROM kya hota hai aur kahan located hota hai?

Answer:

Boot ROM SoC ke andar built-in immutable/low-level boot code hota hai.

Power-up ke baad early execution yahan se start hoti hai.

Iska basic kaam:

Early hardware initialization
Boot source locate karna
Next boot stage load karna
Secure boot verification start karna

Location:

SoC ke andar

Question 8

Android boot sequence Boot ROM se Android OS tak likho.

Answer:

Simplified Android boot:

BOOT ROM → STORAGE ACCESS → BOOTLOADER → RAM INITIALIZATION → KERNEL → SYSTEM/VENDOR COMPONENTS → ANDROID FRAMEWORK → HOME SCREEN

Platform-specific sequence differ kar sakti hai.

Detailed:

SoC Boot ROM executes.
Storage boot data access hota hai.
Primary/secondary bootloader stages run.
RAM initialize/train hoti hai.
Kernel load hota hai.
Hardware drivers initialize.
Android system partitions mount/load.
Android framework/services start.
User interface/home screen.

Question 9

iPhone boot sequence Battery se iOS tak simplified sequence likho.

Answer:

BATTERY → MAIN POWER → PMIC → APPLE SoC → CLOCK/RESET → RAM → BOOT ROM → NAND → SECURE BOOT STAGES → iOS

Important:

Apple architecture strongly secure-boot based hai.

SoC, NAND aur security subsystem closely integrated hote hain.

Question 10

No Power aur No Boot mein exact difference kya hai?

Answer:

No Power

Phone basic startup attempt hi nahi kar raha.

Possible:

Main rail missing
Standby missing
Power-key not recognized
PMIC startup failure

No Boot

Phone electrically power-up karta hai but OS tak nahi pohanchta.

Possible:

CPU execution
RAM
Storage
Firmware
Peripheral issue

Simple Difference:

NO POWER = STARTUP SEQUENCE START NAHI

NO BOOT = START HUI, COMPLETE NAHI HUI

Question 11

No Boot aur No Display mein difference kya hai?

Answer:

No Boot

Phone OS/boot sequence complete nahi karta.

No Display

Phone boot kar sakta hai but screen image nahi dikha rahi.

No-display phone may still:

Ring
Vibrate
Receive calls
PC detect
Play notification sounds

Rule:

BLACK SCREEN KO NO-BOOT MAT SAMJHO JAB TAK BOOT PROVE/FAIL NA HO

Question 12

Logo appear hone se technician ko kaun se major clues milte hain?

Answer:

Logo means significant early stages already work kar chuki hain:

Main power
PMIC startup
SoC execution
Clock/reset
RAM significantly initialized
Storage se at least some boot data read
Display path significantly working

Logo ke baad loop:

Later-stage power, storage, firmware ya peripheral fault ki direction strong karta hai.

Question 13

Always-On rail aur switched rail mein difference explain karo.

Answer:

Always-On Rail

Phone standby/off-like state mein bhi required ho sakti hai.

Used for:

PMIC logic
Power button detection
RTC
Always-on controller

Switched Rail

Specific power state/function mein hi ON hoti hai.

Examples:

Camera rails
Display rails
RF transmit rail
CPU high-performance rail

Lesson:

Switched rail par phone idle state mein 0V normal ho sakta hai.

Question 14

Rail ka 0V reading kab normal ho sakta hai?

Answer:

Jab rail us test state mein:

OFF EXPECTED HO

Examples:

Camera rail when camera app closed.

Backlight output when display asleep.

PA power when phone RF transmit nahi kar raha.

Golden Rule:

0V ≠ FAULT UNTIL RAIL EXPECTED ON

Question 15

Power-state-aware measurement kya hoti hai?

Answer:

Measurement ko phone ki current state ke context mein interpret karna.

Example:

Camera rail check karni hai:

Camera app open honi chahiye.

PA rail check:

Call/data transmit state relevant ho sakti hai.

Display bias:

Screen wake/display-enable state.

Formula:

NET + EXPECTED STATE + MEASUREMENT = CORRECT INTERPRETATION

Section B — Multimeter + Component Testing

Question 16

Resistance mode powered board par kyun normally use nahi karni chahiye?

Answer:

Resistance mode meter apna small test signal/current apply karta hai.

Powered circuit ki external voltage:

Incorrect reading
Meter confusion
Possible damage/risk

create kar sakti hai.

Normally resistance:

POWER REMOVED / BATTERY DISCONNECTED

state mein test karo.

Question 17

Continuity beep ko confirmed short kyun nahi keh sakte?

Answer:

Continuity mode meter ek threshold ke neeche resistance par beep karta hai.

Low resistance naturally ho sakti hai:

CPU rail
GPU rail
Ground path
Coil
Ferrite bead
Low-ohm circuit

Therefore:

BEEP = LOW RESISTANCE CLUE

not:

BEEP = CONFIRMED SHORT

Question 18

CPU VCORE rail par very low resistance milti hai. Kya direct CPU short conclude karoge?

Answer:

Nahi.

CPU VCORE naturally very low resistance ho sakti hai because SoC mein bohat large transistor network hota hai.

Correct process:

Exact rail identify.
Resistance measure.
Known-good same model compare.
Boot behavior observe.
Rail voltage/state check.

Agar known-good bhi similar:

No short.

Question 19

Diode mode ka smartphone repair mein best use kya hai?

Answer:

Best use:

NET SIGNATURE COMPARISON

Especially:

Display connector
USB
SIM
Camera
Touch
Sensor lines

Diode mode abnormal:

Short
Open
ESD fault
Connector/path fault

ka clue de sakti hai.

Question 20

Known-good diode comparison ke liye same model, polarity aur condition kyun useful hain?

Answer:

Diode readings depend kar sakti hain:

IC architecture
Parallel paths
Meter design
Probe polarity
Board revision

Isliye apples-to-apples comparison chahiye.

Best:

Same model + same board revision + same meter + same polarity + power removed.

Question 21

Ek rail ke 20 capacitors continuity beep de rahe hain. Kya 20 capacitors shorted hain?

Answer:

Nahi.

Agar sab same net par hain:

Ek single shorted component poore net ke sab capacitors par same low reading dikhayega.

Correct workflow:

NET IDENTIFY → RAIL RESISTANCE → BOARDVIEW → BRANCHES → CONFIRM COMPONENT

Random caps remove mat karo.

Question 22

Zero-ohm resistor ka role kya ho sakta hai?

Answer:

Zero-ohm resistor almost jumper/link jaisa hota hai.

Uses:

Signal routing
Power branch routing
Configuration
Branch isolation
Manufacturing options

It can also be useful diagnostic separation point.

Question 23

Pull-up resistor kya karta hai? I2C example ke saath explain karo.

Answer:

Pull-up resistor signal line ko positive logic supply se weakly connect karta hai taa ke idle state mein line:

HIGH

rahe.

I2C mein:

SDA aur SCL open-drain type behavior use kar sakte hain.

Pull-up resistor lines ko high state provide karta hai.

Agar pull-up missing/open:

Bus proper high state achieve nahi kar sakta.

Question 24

Current-sense resistor ko bypass kyun nahi karna chahiye?

Answer:

Current-sense resistor system ko current measurement provide karta hai.

Possible uses:

Charging control
Battery monitoring
Protection
Power management

Bypass karne se:

Incorrect current sensing
Protection loss
Unsafe behavior
Wrong charging control

ho sakta hai.

Rule:

CORRECT PART REPAIR KARO — BYPASS NAHI

Question 25

Ferrite bead aur normal power coil mein basic functional difference kya hai?

Answer:

Power Inductor/Coil

Switching regulator mein energy store karta hai.

Example:

Buck converter.

Ferrite Bead

Primarily high-frequency noise filtering/isolation ke liye.

DC par typically low resistance.

Difference:

COIL = POWER CONVERSION/ENERGY STORAGE

FERRITE = NOISE FILTERING

Question 26

Ferrite bead par continuity beep normal kyun ho sakti hai?

Answer:

Ferrite bead ka DC resistance usually bohat low hota hai.

Continuity meter ko wo near-wire jaisa lag sakta hai.

Isliye:

FERRITE BEEP = OFTEN NORMAL

Fault mainly tab:

Open path.

Source-side voltage present but load-side missing.

Question 27

Fuse open mile to next check kya hona chahiye?

Answer:

Sabse important:

DOWNSTREAM SHORT / OVERLOAD CHECK

Because fuse often reason se open hota hai.

Workflow:

Power remove.
Fuse output-side resistance-to-ground.
Downstream net map.
Fault find.
Root cause repair.
Correct fuse restore.

Question 28

Fuse ko bridge karna wrong repair kyun hai?

Answer:

Fuse protection component hai.

Bridge karne se:

Overcurrent protection remove
Shorted circuit ko direct current
Board damage/fire risk

increase hota hai.

Professional rule:

FUSE KA CAUSE FIX KARO, FUSE BYPASS NAHI

Question 29

MOSFET diagnosis ka master formula likho.

Answer:

INPUT → GATE/CONTROL → OUTPUT → LOAD

Also:

Power off par D-S/body-diode comparison useful ho sakti hai.

Question 30

Input MOSFET: input good, gate/control good, output missing, downstream resistance normal. Next direction?

Answer:

MOSFET itself becomes:

STRONG SUSPECT

Because:

Input exists
Drive/control exists
Load not shorted
Output not passing

Still confirm schematic/pinout and measurements before replacement.

Question 31

LDO ka formula likho.

Answer:

VIN → EN → VOUT

Some LDOs may additionally have:

PGOOD
Feedback/control

Question 32

Buck regulator ka simplified diagnostic formula likho.

Answer:

VIN → EN → SWITCHING → INDUCTOR → VOUT → FEEDBACK/PGOOD

Question 33

VIN good, EN missing, OUT missing. Kya regulator replace karna chahiye?

Answer:

Nahi.

Regulator output na dena expected hai if enable missing.

Investigate:

ENABLE / UPSTREAM CONTROL

Possible:

SoC/PMIC command
Pull-up/down
Reset/state condition
Control bus

Question 34

VIN good, EN good, output missing, output resistance normal. Strong suspect?

Answer:

Regulator/LDO itself stronger suspect hota hai.

Reason:

Required input good
Enable command good
Load not obviously shorted
Expected output absent

Still support components/feedback check karo.

Question 35

Crystal ko continuity mode se healthy prove kyun nahi kar sakte?

Answer:

Crystal ka function:

OSCILLATION/FREQUENCY GENERATION

hai.

Continuity sirf DC path check karti hai.

Crystal electrically continuous na hote hue bhi correct oscillator component ho sakta hai.

Correct test:

Oscillation/clock activity appropriate scope/equipment se.

Section C — No Power + PMIC

Question 36

Completely dead phone ka master diagnostic sequence likho.

Answer:

KNOWN-GOOD BATTERY/INPUT

↓

BATTERY CONNECTOR

↓

MAIN RAIL

↓

MAIN RAIL SHORT CHECK

↓

PMIC INPUT

↓

ALWAYS-ON/STANDBY RAILS

↓

POWER-KEY SIGNAL

↓

STARTUP RAILS

↓

CPU/RAM/STORAGE POWER

↓

CLOCK/RESET

↓

BOOT ACTIVITY

Question 37

Known-good battery test no-power diagnosis mein important kyun hai?

Answer:

Weak battery mimic kar sakti hai:

No power
Boot loop
Random restart
Logo loop
Load shutdown

Open-circuit battery voltage normal dikh sakti hai but load par sag kar sakti hai.

Known-good battery fast separator hai:

BATTERY FAULT vs BOARD FAULT

Question 38

Main battery rail missing hai. PMIC se pehle kin stages ko inspect karoge?

Answer:

Check:

Battery itself
Battery connector
Main positive path
Fuse/protection
Input MOSFET/load switch
Broken/open trace

PMIC tab relevant hai jab power actually PMIC tak pohanch rahi ho.

Question 39

Main rail present, PMIC input present, always-on rails absent. Direction?

Answer:

Focus:

PMIC STANDBY GENERATION / ALWAYS-ON OUTPUT / DOWNSTREAM LOAD / PMIC CONTROL

First check:

Always-on rail resistance.

If rail shorted:

Load first.

If resistance normal and required input/control correct:

PMIC standby channel becomes stronger suspect.

Question 40

Always-on rail absent aur resistance very low hai. PMIC replace karne se pehle kya karoge?

Answer:

PMIC replace nahi karna.

Correct workflow:

POWER OFF

↓

EXACT ALWAYS-ON NET IDENTIFY

↓

KNOWN-GOOD RESISTANCE COMPARE

↓

BOARDVIEW PAR CONSUMERS MAP

↓

BRANCH ISOLATE

↓

SHORTED COMPONENT/LOAD CONFIRM

Agar downstream short hai:

PMIC output protection ki wajah se absent ho sakta hai.

Golden Rule:

OUTPUT MISSING + RAIL SHORTED = LOAD FIRST, REGULATOR LATER

Answer Key Part 1 — Questions 1–40 Complete ✅

Next — Answer Key Part 2

Questions 41–80 cover honge:

Power-key + startup sequence
First Missing / First Falling
PMIC diagnosis
Boot loop
RAM/UFS/storage
Charging system
Battery charging safety
Display
LCD/OLED
Touch diagnosis

Part 2 mein hum Question 41 se continue karenge.