EivoTech Laptop & Mobile Repair Master Course
Mobile Repair Course — Part 5
Smartphone RAM + UFS / eMMC / NAND Storage Complete Mastery
Chapter 5: CPU se RAM Initialization, Storage Access aur Operating System Boot Tak Complete Architecture
Smartphone ko boot hone ke liye 3 major digital blocks ki zaroorat hoti hai:
CPU / SoC + RAM + Storage
Simple formula:
CPU instructions execute karta hai
RAM temporary working memory provide karti hai
Storage firmware, OS aur user data permanently save karta hai
In teenon mein se kisi ek ka critical fault phone ko:
Dead-like state
Boot loop
Logo stuck
Recovery mode
Random restart
Freeze
App crash
Storage error
jaisi problems de sakta hai.
1. RAM Kya Hai?
RAM:
Random Access Memory
Phone ki temporary working memory hoti hai.
Phone OFF hone ke baad RAM ka data normally retain nahi hota.
2. RAM ka Basic Kaam
Jab phone boot hota hai:
Storage se required code/data RAM mein load hota hai.
CPU phir RAM se fast access karta hai.
3. Simple Example
Storage = Library.
RAM = Work table.
CPU = Technician.
Book library mein stored hai.
Kaam karte waqt required pages work table par rakhte ho.
Same concept:
Storage permanent.
RAM temporary + fast.
4. Smartphone RAM Types
Modern smartphones commonly use:
LPDDR4
LPDDR4X
LPDDR5
LPDDR5X
depending generation.
5. LPDDR
LPDDR:
Low Power Double Data Rate
Mobile devices ke liye optimized RAM family.
Goal:
High speed.
Low power consumption.
6. Desktop DDR aur LPDDR Difference
Laptop/desktop:
DDR DIMM/SODIMM or soldered DDR.
Mobile:
LPDDR directly board/package architecture mein.
Usually removable module nahi.
7. PoP RAM
Many smartphones use:
Package on Package
Architecture.
SoC lower package.
RAM upper package.
8. PoP Advantage
Space saving.
Short electrical paths.
High-speed memory interface.
9. PoP Diagnostic Challenge
RAM physically CPU ke upar hone ki wajah se:
Direct pins accessible nahi.
High-speed signals microscope se direct probe karna practical nahi.
Diagnosis indirect evidence se hota hai.
10. RAM ko Kya Chahiye?
RAM ko generally:
Power rails.
Clock/strobe signals.
Command/address.
Data lines.
Initialization/training.
chahiye.
Exact LPDDR architecture generation-specific.
11. RAM Power Rails
Possible categories:
Core supply.
I/O supply.
Reference-related supplies.
Exact names/voltages schematic/platform-specific.
12. RAM Voltage Memorize Mat Karo
Different LPDDR generations different voltage domains use karti hain.
Always use:
Schematic.
Board documentation.
Known-good comparison.
13. RAM Rail Missing
Possible symptoms:
No boot.
Boot loop.
No logo.
Low-level recovery mode.
Repeated reset.
14. RAM Rail Present
This proves only:
Power available.
It does not prove:
RAM package healthy.
Data lines healthy.
Training successful.
15. RAM Initialization
Boot ke early stage par CPU/boot firmware RAM ko initialize karta hai.
16. RAM Training
High-speed memory system ko correct timings/parameters establish karne hote hain.
Is process ko generally:
Memory training
kehte hain.
17. Training Fail
If training fails:
System may:
Reset.
Hang.
Remain black.
Enter diagnostic/recovery state.
18. Smartphone RAM Training Laptop Jaisa?
Concept same hai:
Memory ko usable state mein initialize karna.
Implementation platform-specific.
19. RAM Fault Symptoms
Possible:
Random restarts.
Boot loop.
Freeze.
App crashes.
Kernel panic.
No boot.
But these symptoms RAM-specific proof nahi.
20. RAM Fault vs Software Fault
A software bug bhi:
Restart.
Freeze.
App crash.
create kar sakta hai.
Therefore hardware conclusion se pehle evidence chain chahiye.
21. RAM Fault After Drop
Possible:
PoP solder joint issue.
Board flex.
Cracked nearby components.
Power rail damage.
But random CPU/RAM heating first step nahi.
22. RAM Fault After Liquid Damage
Could be:
Corrosion on related power/control components.
Not necessarily RAM package itself.
23. RAM BGA / PoP Fault
Strong evidence tab:
Power rails correct.
Storage/firmware considered.
Known-good software state.
Boot failure pattern consistent.
Other external faults ruled out.
24. Storage Kya Hai?
Storage phone ki permanent memory hai.
Contains:
Boot firmware.
Operating system.
Apps.
Photos.
Videos.
Messages.
User data.
Configuration.
25. Main Smartphone Storage Types
Common:
UFS.
eMMC.
NAND-based proprietary/integrated architectures.
26. UFS
UFS:
Universal Flash Storage
Modern smartphones mein common high-speed embedded storage.
27. eMMC
eMMC:
embedded MultiMediaCard
Older/lower-end phones mein common.
Contains:
Flash memory + controller.
28. NAND
NAND is flash-memory technology.
Repair language mein especially iPhone context mein storage IC ko often:
NAND
bola jata hai.
29. UFS vs eMMC
UFS generally:
Higher performance.
Full-duplex style command/data capabilities.
Modern serial interface.
eMMC:
Older embedded interface.
Lower performance compared with newer UFS.
30. Storage IC ke Andar
Storage package may include:
NAND flash cells.
Controller.
Error correction.
Wear management.
Protocol logic.
31. Controller Kyun Important?
CPU raw NAND cells directly manage nahi karta in normal UFS/eMMC architecture.
Storage controller handles:
Bad blocks.
Wear leveling.
ECC.
Logical addressing.
32. ECC
ECC:
Error Correcting Code
Storage data errors detect/correct karne mein help karta hai.
33. Wear Leveling
Flash memory cells limited write cycles rakhti hain.
Controller writes ko distribute karta hai.
34. Bad Blocks
Flash media mein some blocks unusable ho sakte hain.
Controller normally manage karta hai.
35. Storage Health Degrade
Over time storage can develop:
Read errors.
Write errors.
Slow response.
Bad blocks.
Controller faults.
36. Storage Fault Symptoms
Possible:
Logo stuck.
Boot loop.
Apps crash.
System freeze.
File corruption.
Recovery mode.
Unable to update/restore.
Unexpected restart.
37. Storage Fault ≠ Every Boot Loop
Boot loop can also be:
Battery.
PMIC rail.
RAM.
Firmware.
Peripheral.
Thermal.
38. UFS Power Requirements
UFS usually multiple supplies use karta hai.
Conceptually:
Core supply.
I/O supply.
Possibly additional supply depending generation.
39. UFS Main Diagnostic Formula
POWER → RESET → CLOCK → DATA INTERFACE → STORAGE RESPONSE
40. UFS Power Missing
CPU boot starts but storage access fail ho sakta hai.
Phone low-level mode mein remain kar sakta hai.
41. UFS Power Present
Does not prove UFS working.
Still need:
Reset.
Clock.
Communication.
42. UFS Reset
Storage device ko correct reset state se release hona hota hai.
Reset stuck:
No storage communication.
43. UFS Reference Clock
High-speed storage needs timing/reference.
Clock missing:
No proper communication.
44. UFS Data Lanes
High-speed differential links.
These are signal-integrity-sensitive.
45. UFS Data Trace Repair
Random long jumper:
Professional repair nahi.
High-speed routing matters.
46. eMMC Signals
eMMC conceptually uses:
Clock.
Command.
Data lines.
Power rails.
Reset depending device/platform.
47. eMMC Power Missing
No communication.
No boot.
48. eMMC Clock Present
Useful clue:
SoC attempting communication.
But one clock waveform alone storage health proof nahi.
49. Storage Access Boot Sequence
CPU Boot ROM
↓
Storage controller initializes.
↓
Boot data requested.
↓
Bootloader read.
↓
Loaded into RAM.
↓
CPU executes next stage.
50. CPU, RAM aur Storage Relationship
Boot ke liye teenon interdependent hain.
Example:
Storage bootloader provide karta hai.
RAM bootloader ko working space deti hai.
CPU execute karta hai.
51. Storage Read but RAM Fail
CPU next stage execute nahi kar payega properly.
Symptoms storage fault jaisi lag sakti hain.
52. RAM Good but Storage Dead
CPU Boot ROM start karega but normal OS boot nahi.
Possible low-level USB mode.
53. Storage Good but CPU Power Fault
Storage completely okay ho sakti hai but phone dead.
No need storage work.
54. Boot ROM Storage ko Access Kab Karta Hai?
Early boot stage mein.
Exact sequence platform-specific.
55. Boot Partition
Storage mein special boot areas/partitions hoti hain.
Contain:
Bootloader.
Security metadata.
Firmware components.
56. Android Storage Layout
Modern Android devices multiple partitions use karte hain.
Examples conceptually:
Boot-related.
System.
Vendor.
User data.
Recovery-related.
Exact names/device vary.
57. Partition Corruption
Phone hardware healthy ho sakta hai but corrupted boot partition:
No boot.
Boot loop.
Recovery.
58. Hardware Storage Failure
Physical storage controller/NAND failure:
Read/write errors.
Restore failures.
Persistent boot issues.
59. Software Corruption vs Hardware Storage
Very important difference.
Software corruption:
Storage hardware still reliable.
Hardware failure:
Repeated read/write issues may continue after legitimate firmware restoration attempts.
60. Firmware Restore Failure
Restore/update failing does not automatically mean UFS/NAND bad.
Could be:
USB issue.
Battery instability.
Software package.
Connection.
Other hardware fault.
61. Error Codes
Brand tools may show error codes.
Use them as clues.
Not every error code directly identifies a component.
62. Storage Current/Heat
UFS/NAND may warm during activity.
Heat alone:
Not fault proof.
63. UFS Abnormal Heat
If storage chip immediately abnormally hot with boot failure:
Possible internal fault or power issue.
Need rail/current evidence.
64. Storage Cold
Could mean:
No storage rail.
No clock.
No activity.
Deep sleep.
Not automatically dead.
65. UFS Short
If specific UFS supply rail has abnormally low resistance:
Could be:
Storage IC.
External capacitor.
Other same-rail load.
Need isolation.
66. UFS Rail Beep
As always:
Continuity beep alone not enough.
67. Storage Rail Known-Good Comparison
Very useful.
Compare same platform:
Resistance.
Diode readings.
Boot-stage voltage.
68. Storage Power-State Timing
Some storage rails may appear only after button/boot request.
Phone off par 0V can be normal.
69. RAM Power-State Timing
Same:
RAM full rails may not be present in deep-off state.
70. No-Boot Diagnostic Order
If phone does not boot:
Main battery stable?
↓
PMIC rails?
↓
CPU rails?
↓
RAM rails?
↓
Storage rails?
↓
Reset/clock?
↓
USB boot mode?
↓
Firmware/storage deeper diagnosis.
71. Boot Logo Proves What?
At minimum, significant portions of:
CPU.
RAM.
Storage.
Display
have functioned enough to reach logo.
72. Logo Stuck
Focus later:
Storage read.
System partitions.
Peripheral initialization.
Software.
Power stability.
73. Logo Then Restart
Could be:
Boot process crash.
Battery voltage collapse.
RAM instability.
Storage error.
Peripheral short.
74. Recovery Mode
If phone reliably enters recovery:
SoC.
RAM.
Display.
Some storage/firmware functions
are working.
75. Fastboot / Download Mode
If phone reaches manufacturer boot mode:
This is strong evidence against completely dead SoC/PMIC.
76. Low-Level USB Mode
Can indicate:
Boot ROM active but later boot stage unavailable.
This makes storage/boot-chain diagnosis important.
77. RAM Fault vs UFS Fault — Basic Difference
RAM fault may appear as:
Very early instability.
Random crashes.
Training failure.
Unpredictable restart.
Storage fault may appear as:
Read/write errors.
Logo stuck.
Restore/update failure.
Partition errors.
But overlap bohat hai.
78. Stronger RAM Evidence
Known power rails correct.
Boot firmware/storage accessible.
Crashes vary under memory-heavy load.
Logs/diagnostics point memory-related.
Physical PoP evidence.
Still platform-specific.
79. Stronger Storage Evidence
Repeated read/write errors.
Persistent storage-related restore failures.
Boot mode sees device but cannot access storage properly.
Storage power/clock/reset verified.
80. Software Flashing Rule
Don't reflash blindly.
If phone has customer data:
Data impact understand karo.
Authorized restoration only.
81. Factory Reset
Erases user data.
Not diagnostic first step when data preservation matters.
82. Customer Data Priority
If phone has valuable data and storage is suspected:
Avoid unnecessary erase/restore operations.
83. Encryption
Modern phones encrypt user data.
Storage chip alone may not be enough to recover readable data.
Security keys can be tied to original SoC/hardware.
84. SoC + Storage Pair Importance
Especially modern secure phones:
Original SoC/storage/security data relationship important.
Major chip replacement can destroy access to customer data.
85. iPhone NAND Concept
iPhone NAND storage stores system/user information.
But data encryption/security architecture ties critical access to device hardware.
Detailed iPhone section later.
86. Android UFS Security
Modern Android also uses:
Encryption.
Secure boot.
Hardware-backed keys.
So storage swapping is not simple data-recovery solution.
87. UFS Replacement
Replacing UFS is advanced work.
Requires exact compatibility, programming/configuration and data/security awareness.
Not first-line diagnosis.
88. eMMC Replacement
Same principle:
Advanced board/storage procedure.
Need exact device support.
89. Random UFS Reflow
Avoid.
Heating can:
Damage storage.
Warp board.
Damage SoC/RAM nearby.
Create temporary misleading behavior.
90. UFS Underfill
Some storage chips may use adhesive/underfill depending device.
Makes rework more complex.
91. Storage Physical Damage
Drop can cause:
BGA solder cracks.
Board flex.
Nearby capacitor cracking.
Connector/flex issues.
Before chip conclusion inspect entire area.
92. RAM Physical Damage
PoP area may be affected by:
Board bending.
Drop.
Previous heating.
But diagnose systematically.
93. Storage Power Regulator Fault
Phone may have good storage IC but missing one UFS rail.
Then replacing UFS is wrong.
94. Example
CPU rails ✅
RAM rail ✅
UFS VCC rail ✅
UFS I/O rail ❌
Regulator enable ✅
Output absent.
Direction:
Storage supply stage.
95. UFS Reset Fault Example
All UFS rails present.
Reference clock present.
Reset stays active.
Direction:
Reset/control path.
96. UFS Clock Fault Example
Rails correct.
Reset released.
No clock.
Direction:
Clock generation/path.
97. UFS Communication Fault Example
Power/clock/reset all good.
No expected storage communication.
Then:
UFS/data path/SoC controller becomes stronger.
98. eMMC Clock Activity
If scope shows eMMC clock attempts:
SoC is trying to access storage.
Useful evidence.
99. Boot Loop with UFS Errors
Phone repeatedly restarts.
Storage read failures appear in legitimate diagnostic logs.
This strongly supports storage side.
100. Random Restart Under Heavy Apps
Could be:
RAM.
Battery.
Thermal.
Software.
Storage.
Need broader diagnosis.
101. Memory-Heavy Test
If authorized functioning phone crashes only under heavy memory workload:
RAM subsystem becomes one possible direction.
But don't deliberately overstress unstable customer phone.
102. Storage-Heavy Test
Read/write errors during normal diagnostic operations can reveal storage issues.
Avoid destructive testing when customer data matters.
103. Storage Capacity Wrong
Phone may report unexpected storage capacity after previous repair.
Possible:
Wrong programmed storage.
Firmware/configuration issue.
Storage replacement issue.
104. Storage Not Detected at All
Check:
Power.
Reset.
Clock.
Communication.
Then storage itself.
105. Phone Shows 0GB / Abnormal Capacity
Strong storage/configuration clue.
Exact platform needed.
106. Read-Only Behavior
Failing flash can sometimes develop inability to reliably write data.
Symptoms:
Updates fail.
Settings revert.
Apps fail.
Storage-related errors.
107. Slow Storage
Phone can become extremely slow due storage degradation.
But first also consider:
Thermal throttling.
Low free space.
Software.
Battery/power.
108. RAM Cannot Be Tested Like Laptop SODIMM
Mobile RAM soldered/PoP.
No easy module swap.
Therefore indirect diagnostics more important.
109. Storage Module Swap Also Not Simple
Because:
BGA.
Security.
Programming.
Data.
110. BoardView for RAM/UFS
Use BoardView to locate:
RAM-related capacitors.
UFS rails.
Clock/reset components.
Test points.
111. Schematic for UFS
Search:
UFS IC reference.
Then map:
VCC.
VCCQ/VCCQ2 or equivalent.
RESET.
REFCLK.
Data lanes.
Exact naming varies.
112. Safer Test Points
Use:
Supply capacitor.
Series resistor.
Clock test pad where provided.
Reset resistor.
Avoid direct BGA balls.
113. High-Speed Lines
UFS/RAM data lines:
Do not casually probe with large tips.
Can disturb signal or cause shorts.
114. RAM Data Lines
Very high-speed and dense.
Normal repair diagnosis rarely involves individual line voltage checks.
Use power/boot evidence instead.
115. RAM Power Rail Short
Could involve:
RAM package.
SoC because PoP/shared domain.
Capacitors.
PMIC.
Need comparison before major conclusion.
116. UFS Rail Short
Easier to isolate sometimes because storage is separate package.
But still no random chip removal first.
117. Main Rail vs Storage Rail
If phone completely dead:
Main power first.
If phone reaches logo:
Storage diagnosis more relevant.
118. Storage Fault After Firmware Update
If update interrupted:
Software corruption possible.
Do not assume physical UFS failure.
119. Storage Fault After Drop
If immediately after drop:
Physical/BGA/board issue becomes more plausible.
120. Storage Fault After Liquid
Check nearby:
Corrosion.
Power components.
Clock/reset resistors.
before storage IC.
121. RAM Fault After Previous CPU Rework
Previous CPU heat/rework can affect PoP RAM.
This is why repair history matters.
122. Logs
Modern phones may generate diagnostic crash logs.
These can help distinguish:
Memory.
Storage.
Thermal.
Watchdog.
Peripheral.
Exact interpretation platform-specific.
123. Panic / Watchdog Logs
A restart log can identify failing subsystem direction.
But one log line should not be interpreted without context.
124. Repeated Same Error
Repeated same subsystem error across multiple boots is stronger evidence.
125. RAM Diagnostic Formula
POWER → INITIALIZATION → TRAINING → STABILITY
126. Storage Diagnostic Formula
POWER → RESET → CLOCK → COMMUNICATION → READ/WRITE → BOOT
127. Combined Boot Formula
CPU BOOT ROM → RAM INIT → STORAGE ACCESS → BOOTLOADER → OS
128. No-Boot Example 1
Battery good.
PMIC good.
CPU rails good.
RAM rail 0V.
Direction:
RAM power.
Not UFS first.
129. No-Boot Example 2
CPU/RAM rails good.
UFS rail missing.
Direction:
Storage power.
130. No-Boot Example 3
All rails good.
UFS reset stuck.
Direction:
Storage reset/control.
131. No-Boot Example 4
Power/reset/clock good.
Phone enters low-level USB mode.
Normal boot unavailable.
Direction:
Storage/firmware deeper diagnosis.
132. Boot-Loop Example
Phone reaches logo.
Battery voltage stable.
Peripheral isolation no change.
Repeated storage read errors.
Direction:
Storage/firmware.
133. RAM Example
Phone crashes randomly across different tasks.
Storage diagnostics normal.
Memory-related crash evidence repeated.
Direction:
RAM/SoC memory subsystem.
134. External Peripheral Example
Phone boot loops.
Disconnect damaged fingerprint flex.
Phone boots.
Lesson:
Do not blame UFS because logo loop exists.
135. Battery Example
Phone logo then off.
Known-good battery fixes.
Lesson:
Battery can mimic storage/RAM fault.
136. Thermal Example
Phone runs until hot then restarts.
Direction:
Thermal/power before RAM/UFS.
137. UFS Diagnostic Worksheet
Phone Model: __________
Platform: __________
Storage Type: UFS / eMMC / NAND
Storage Part Number: __________
Main Storage Rail: __________
I/O Rail: __________
Additional Rail: __________
Reset State: __________
Clock Evidence: __________
USB Boot Mode: __________
Storage Heat: Normal / Abnormal
Boot Stage: __________
Restore/Update Behavior: __________
Data Important: Yes / No
Final Fault Direction: __________
138. RAM Diagnostic Worksheet
RAM Type: __________
PoP / Separate: __________
RAM Rail 1: __________
RAM Rail 2: __________
Boot Reaches Logo: Yes / No
USB Detection: __________
Random Restarts: Yes / No
Memory-related Logs: __________
Previous CPU Work: Yes / No
Drop/Liquid History: __________
Final Fault Direction: __________
139. RAM vs Storage Comparison Table
| Symptom | RAM Direction | Storage Direction |
|---|---|---|
| Very early boot fail | Possible | Possible |
| Logo stuck | Possible | Strong |
| Read/write errors | Weak | Strong |
| Random memory-related crashes | Strong | Possible |
| Restore consistently fails storage access | Weak | Strong |
| Low-level USB mode | Possible | Stronger storage/boot clue |
| RAM rail missing | Strong power clue | Weak |
| UFS rail missing | Weak | Strong |
This table clue hai, universal proof nahi.
140. Common Beginner Mistake 1
Boot loop = UFS bad.
141. Common Beginner Mistake 2
Logo stuck = RAM bad.
142. Common Beginner Mistake 3
UFS hot = UFS short.
143. Common Beginner Mistake 4
UFS rail 0V while phone off = fault.
144. Common Beginner Mistake 5
Customer data ki parwah ke baghair firmware erase.
145. Common Beginner Mistake 6
CPU/RAM random heat.
146. Common Beginner Mistake 7
UFS replace before checking power/reset/clock.
147. Common Beginner Mistake 8
eMMC/UFS high-speed lines ko normal jumper wires jaisa treat karna.
148. Common Beginner Mistake 9
Battery fault ko storage fault samajhna.
149. Common Beginner Mistake 10
One error code ko exact IC diagnosis samajhna.
150. RAM Golden Rules
1. Mobile RAM normally soldered/PoP hoti hai.
2. RAM power present hona RAM health prove nahi karta.
3. Memory initialization early boot stage hai.
4. PoP repair advanced BGA work hai.
5. Random RAM/CPU heating diagnostic method nahi.
151. Storage Golden Rules
1. UFS/eMMC ko power + reset + clock + communication chahiye.
2. Storage fault boot loop/no boot create kar sakta hai.
3. Boot loop automatically storage fault nahi.
4. UFS power missing ho to chip replace mat karo; supply diagnose karo.
5. Customer data important ho to destructive restore/erase avoid karo.
6. High-speed UFS lines signal-integrity sensitive hain.
7. Storage security modern phones mein SoC/hardware ke saath linked ho sakti hai.
152. Part 5 Quick Revision
LPDDR
Low-power smartphone RAM.
PoP
RAM SoC ke upar stacked package.
RAM Training
Memory timing/configuration initialization.
UFS
Modern high-speed flash storage.
eMMC
Older embedded flash storage.
NAND
Flash-memory technology.
ECC
Storage data errors correct karne ka system.
Wear Leveling
Writes ko flash cells par distribute karna.
Boot Partition
Early boot firmware area.
Storage Reset
Storage initialization control signal.
REFCLK
Storage timing reference.
153. Part 5 ka Sabse Important Lesson
Phone boot ko is chain mein samjho:
CPU BOOT ROM → RAM INITIALIZE → STORAGE ACCESS → BOOTLOADER → OS
Agar RAM power missing:
Storage ko blame mat karo.
Agar UFS power/reset/clock missing:
UFS IC ko immediately bad mat bolo.
Agar phone logo show kar raha hai:
CPU, RAM aur storage already significant amount of work kar chuke hain.
Aur agar customer ka important data hai:
DATA PRESERVATION REPAIR SE PEHLE SOCHO
Professional technician ka kaam sirf phone boot karwana nahi — customer ka hardware aur data dono protect karna hai.
Mobile Repair Course — Part 5 Complete
Next — Mobile Part 6: Smartphone Charging Circuit + USB Complete Mastery
Part 6 mein hum cover karenge:
USB-C / Micro-USB basic charging path.
VBUS.
CC1 / CC2 introduction.
ESD protection.
OVP.
Charging IC.
Power-path management.
Battery charging stages.
Battery temperature/detect.
USB data D+ / D-.
Fast charging concepts.
USB PD basics.
Qualcomm Quick Charge concepts.
No charging.
Slow charging.
Charging disconnect.
PC detection issues.
Port vs motherboard fault.
Aur complete:
CHARGER → PORT → PROTECTION → CHARGER IC → BATTERY
diagnostic workflow.
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