1. Dust on coil?

2. Fan spinning?

3. Ice blocking freezer coil?

4. Compressor, Capacitor, Relay

PCI-Express 16x PinOut 


Pin 
Side B Connector 
Side A Connector 

# 
Name 
Description 
Name 
Description 

1 
+12v 
+12 volt power 
PRSNT#1 
Hot plug presence detect 

2 
+12v 
+12 volt power 
+12v 
+12 volt power 

3 
+12v 
+12 volt power 
+12v 
+12 volt power 

4 
GND 
Ground 
GND 
Ground 

5 
SMCLK 
SMBus clock 
JTAG2 
TCK 

6 
SMDAT 
SMBus data 
JTAG3 
TDI 

7 
GND 
Ground 
JTAG4 
TDO 

8 
+3.3v 
+3.3 volt power 
JTAG5 
TMS 

9 
JTAG1 
+TRST# 
+3.3v 
+3.3 volt power 

10 
3.3Vaux 
3.3v volt power 
+3.3v 
+3.3 volt power 

11 
WAKE# 
Link Reactivation 
PWRGD 
Power Good 


Mechanical Key 

12 
RSVD 
Reserved 
GND 
Ground 

13 
GND 
Ground 
REFCLK+ 
Reference Clock

Differential pair 

14 
HSOp(0) 
Transmitter Lane 0,

Differential pair 
REFCLK- 

15 
HSOn(0) 
GND 
Ground 

16 
GND 
Ground 
HSIp(0) 
Receiver Lane 0,

Differential pair 

17 
PRSNT#2 
Hotplug detect 
HSIn(0) 

18 
GND 
Ground 
GND 
Ground 

19 
HSOp(1) 
Transmitter Lane 1,

Differential pair 
RSVD 
Reserved 

20 
HSOn(1) 
GND 
Ground 

21 
GND 
Ground 
HSIp(1) 
Receiver Lane 1,

Differential pair 

22 
GND 
Ground 
HSIn(1) 

23 
HSOp(2) 
Transmitter Lane 2,

Differential pair 
GND 
Ground 

24 
HSOn(2) 
GND 
Ground 

25 
GND 
Ground 
HSIp(2) 
Receiver Lane 2,

Differential pair 

26 
GND 
Ground 
HSIn(2) 

27 
HSOp(3) 
Transmitter Lane 3,

Differential pair 
GND 
Ground 

28 
HSOn(3) 
GND 
Ground 

29 
GND 
Ground 
HSIp(3) 
Receiver Lane 3,

Differential pair 

30 
RSVD 
Reserved 
HSIn(3) 

31 
PRSNT#2 
Hot plug detect 
GND 
Ground 

32 
GND 
Ground 
RSVD 
Reserved 

33 
HSOp(4) 
Transmitter Lane 4,

Differential pair 
RSVD 
Reserved 

34 
HSOn(4) 
GND 
Ground 

35 
GND 
Ground 
HSIp(4) 
Receiver Lane 4,

Differential pair 

36 
GND 
Ground 
HSIn(4) 

37 
HSOp(5) 
Transmitter Lane 5,

Differential pair 
GND 
Ground 

38 
HSOn(5) 
GND 
Ground 

39 
GND 
Ground 
HSIp(5) 
Receiver Lane 5,

Differential pair 

40 
GND 
Ground 
HSIn(5) 

41 
HSOp(6) 
Transmitter Lane 6,

Differential pair 
GND 
Ground 

42 
HSOn(6) 
GND 
Ground 

43 
GND 
Ground 
HSIp(6) 
Receiver Lane 6,

Differential pair 

44 
GND 
Ground 
HSIn(6) 

45 
HSOp(7) 
Transmitter Lane 7,

Differential pair 
GND 
Ground 

46 
HSOn(7) 
GND 
Ground 

47 
GND 
Ground 
HSIp(7) 
Receiver Lane 7,

Differential pair 

48 
PRSNT#2 
Hot plug detect 
HSIn(7) 

49 
GND 
Ground 
GND 
Ground 

50 
HSOp(8) 
Transmitter Lane 8,

Differential pair 
RSVD 
Reserved 

51 
HSOn(8) 
GND 
Ground 

52 
GND 
Ground 
HSIp(8) 
Receiver Lane 8,

Differential pair 

53 
GND 
Ground 
HSIn(8) 

54 
HSOp(9) 
Transmitter Lane 9,

Differential pair 
GND 
Ground 

55 
HSOn(9) 
GND 
Ground 

56 
GND 
Ground 
HSIp(9) 
Receiver Lane 9,

Differential pair 

57 
GND 
Ground 
HSIn(9) 

58 
HSOp(10) 
Transmitter Lane 10,

Differential pair 
GND 
Ground 

59 
HSOn(10) 
GND 
Ground 

60 
GND 
Ground 
HSIp(10) 
Receiver Lane 10,

Differential pair 

61 
GND 
Ground 
HSIn(10) 

62 
HSOp(11) 
Transmitter Lane 11,

Differential pair 
GND 
Ground 

63 
HSOn(11) 
GND 
Ground 

64 
GND 
Ground 
HSIp(11) 
Receiver Lane 11,

Differential pair 

65 
GND 
Ground 
HSIn(11) 

66 
HSOp(12) 
Transmitter Lane 12,

Differential pair 
GND 
Ground 

67 
HSOn(12) 
GND 
Ground 

68 
GND 
Ground 
HSIp(12) 
Receiver Lane 12,

Differential pair 

69 
GND 
Ground 
HSIn(12) 

70 
HSOp(13) 
Transmitter Lane 13,

Differential pair 
GND 
Ground 

71 
HSOn(13) 
GND 
Ground 

72 
GND 
Ground 
HSIp(13) 
Receiver Lane 13,

Differential pair 

73 
GND 
Ground 
HSIn(13) 

74 
HSOp(14) 
Transmitter Lane 14,

Differential pair 
GND 
Ground 

75 
HSOn(14) 
GND 
Ground 

76 
GND 
Ground 
HSIp(14) 
Receiver Lane 14,

Differential pair 

77 
GND 
Ground 
HSIn(14) 

78 
HSOp(15) 
Transmitter Lane 15,

Differential pair 
GND 
Ground 

79 
HSOn(15) 
GND 
Ground 

80 
GND 
Ground 
HSIp(15) 
Receiver Lane 15,

Differential pair 

81 
PRSNT#2 
Hot plug present detect 
HSIn(15) 

82 
RSVD#2 
Hot Plug Detect 
GND 
Ground 

23 cây treated pine

 https://www.bunnings.com.au/70-x-35mm-framing-mgp10-h2-blue-pine-2-4m_p8030953

10 tấm gyprock

https://www.bunnings.com.au/gyprock-csr-2400-x-1200-x-10mm-2-88sqm-plasterboard-re_p0731415

🔋 1. Battery (VBAT) Supplies Standby Power

• The VBAT (Main Battery Line) is always connected to the logic board, even when the iPhone is off.
• VBAT voltage: ~3.7V-4.2V, depending on battery charge.

⚠️ If VBAT is missing or disconnected, the iPhone will not turn on, even when plugged into a charger.

⚡ 2. Power Management IC (PMIC) is Always Active

• PMIC (Power Management Integrated Circuit) remains partially active to manage charging, power button detection, and wake-up events.
• PMIC generates low-power standby voltages to supply essential circuits.
• These voltages keep the iPhone "ready to turn on" when needed.

⚠️ If PMIC fails, the iPhone will be completely dead (no charging, no response).

📶 3. Always-On Power Rails (Even When Off)

Some power rails remain active even when the phone is off, including:

These power rails allow the phone to detect button presses, wake up from alarms, charge, and send signals for Find My iPhone.

🔄 4. Components That Stay Powered

Even when the phone appears off, the following components remain powered in a low-energy state:

🕰️ A. Real-Time Clock (RTC)

• RTC keeps track of time and alarms.
• Stored in a small, low-power memory circuit powered by PP3V0_TRTC.
• Even if the battery is removed, the RTC may still work for a short period using capacitor-stored energy.

📡 B. Find My iPhone / Low-Power Baseband

• iPhones with Find My enabled can still send location updates even when "powered off."
• The Baseband Processor (BB) receives low-power signals from PP1V8_ALWAYS to send a location beacon.
• The Bluetooth & UWB chip (for Find My) stays in a low-energy mode.

🔌 C. Charging Circuit & Lightning Port Detection

• The charging circuit (Tristar/Tigris ICs) remains active to detect power input from a charger.
• If you plug in a Lightning cable, the phone can boot up into the charging screen.
• The PP_CHARGER (5V) line remains active when plugged in.

🖲️ D. Power Button & Wake-Up Logic

• The Power Button Circuit (PP1V8_ALWAYS) remains active to detect when you press the power button.
• When you press the power button, AP_TO_PM_ENABLE signals the PMIC to wake up the CPU.

⚠️ If the iPhone is Completely Dead (No Response to Charging or Power Button)

Possible reasons:

1. No VBAT power → Dead battery or disconnected battery.
2. PMIC failure → No power regulation to critical components.
3. PP1V8_ALWAYS missing → No standby power for essential circuits.
4. Damaged power button circuit → Cannot trigger wake-up sequence.

🛠️ Summary: Which Components Have Power When iPhone is Off?

🚀 Final Thoughts

Even when an iPhone is turned off, certain power rails remain active to handle charging, wake-up events, and Find My iPhone functions. The PMIC regulates low-power circuits to keep the device in a ready state.

If an iPhone is completely dead and unresponsive, the issue is likely a power rail failure, PMIC malfunction, or battery disconnection.

🔋 1. Power Source & Initial Activation

This stage involves powering the device and initializing voltage regulators.

Step 1: Battery or Charger Supplies Power

• The iPhone receives power from either:

  • The battery (connected via VBAT)
  • The Lightning port (if charging or connected to a computer)

• VBAT Line (Main Battery Line)

  • VBAT is the main power rail connected directly to the battery.
  • It supplies raw battery voltage (3.7V - 4.35V) to the Power Management IC (PMIC).
  • If VBAT is missing or disrupted, the phone will not power on.

⚡ 2. Power Management & Voltage Regulation

Step 2: Power Management IC (PMIC) Activation

• The PMIC (Power Management Integrated Circuit) is responsible for regulating voltage and distributing power to various components.
• The PMIC is controlled by the AP_TO_PM_ENABLE signal, which is triggered when the power button is pressed.

Step 3: PMIC Generates Power Rails

The PMIC takes the raw VBAT voltage and converts it into different power rails:

• If PMIC fails to generate these power rails, the iPhone will not boot.

🧠 3. CPU & BootROM Execution

Step 4: CPU (Application Processor) Power-On

• The A-series chip (e.g., A15, A16) is now powered by PP_CPU and PP_GPU.
• The clock signal is provided by the Crystal Oscillator (XTAL) at 19.2 MHz, which keeps all components synchronized.
• The CPU executes the BootROM code stored in read-only memory (ROM).

Step 5: Secure Boot & NAND Flash Activation

• BootROM initializes the NAND flash storage (internal memory) via the PP_NAND power rail.
• It reads system firmware and loads the Low-Level Bootloader (LLB).
• If the NAND chip is faulty, the iPhone will not boot or get stuck on the Apple logo.

📡 4. Display, Sensors, & Communication Circuits Power Up

Step 6: Power Sent to Peripherals

Once the firmware is verified, PMIC enables additional power rails for:

• PP_DISPLAY → Powers the LCD/OLED screen
• PP_TOUCH → Activates the touchscreen controller
• PP_CAM → Powers the front and rear cameras

If these power rails are missing, you may experience:

• No display (but device still works)
• Touchscreen not responding
• No Face ID or Camera detection

📶 5. Baseband & Wireless Components Power Up

Step 7: Cellular & Wireless Radios Initialize

• The Baseband Processor (handles SIM, cellular communication) is powered by:
  • PP_VDD_BB (Baseband Main Power)
  • PP_VDD_BB_SRAM (Baseband Memory Power)
• The Wi-Fi/Bluetooth/FM Radio chip (Broadcom or Qualcomm) is powered by:
  • PP_WIFI (Wi-Fi Power Rail)

If these rails fail, the iPhone may show:
❌ No Service (Baseband problem)
❌ Wi-Fi Greyed Out

📲 6. Graphical Interface & System Boot-Up

Step 8: SpringBoard (Graphical UI) Loads

• Once all hardware is powered, the SpringBoard UI is loaded from NAND storage.
• The backlight is powered by PP_BACKLIGHT.
• The iPhone is now in the setup screen or home screen.

⚠️ Troubleshooting Electrical Boot Failures

If an iPhone fails to boot, checking power rails with a multimeter can help diagnose the issue.

🔑 Summary of iPhone Electrical Startup Process

🚀 Final Thoughts

This is the complete electrical startup process of an iPhone, explaining how electricity flows through VBAT, PMIC, power rails, and components. If you're troubleshooting boot failures, checking voltages at these power rails can help identify hardware issues.

🔹 Stage 1: Power-On & Hardware Initialization

This stage handles the basic power flow and hardware activation.

1️⃣ Power Button Pressed

• Pressing the power button signals the PMU (Power Management Unit) to begin powering up the device.
• PMU activates components like:
  • CPU (Processor)
  • RAM (Random Access Memory)
  • NAND Storage (Flash Memory)
  • Baseband Processor (For Cellular Communication)
  • Battery Management System

🔹 Stage 2: BootROM Execution (First Bootloader - Immutable Code)

Now that the device has power, the processor executes BootROM, the first-stage bootloader stored in read-only memory (ROM) inside the CPU.

2️⃣ BootROM Execution

• BootROM is the first line of defense in iOS security and cannot be modified.
• It performs an Initial Integrity Check to verify if the firmware is valid.
• It loads the Apple Secure Boot Chain, a multi-step process ensuring only Apple-approved software is used.

🔹 Stage 3: Secure Boot Chain & Low-Level Bootloading

BootROM now begins executing the next stage of the boot process:

3️⃣ Loading the LLB (Low-Level Bootloader)

• LLB (Low-Level Bootloader) is loaded into RAM.
• It checks the iBoot signature (the next bootloader) to confirm it hasn’t been tampered with.
• If LLB verification fails, the iPhone will enter Recovery Mode.

🔹 Stage 4: iBoot & Firmware Verification

Once the LLB verifies iBoot, the system moves forward.

4️⃣ Loading iBoot (Second-Stage Bootloader)

• iBoot is responsible for verifying and loading the iOS kernel.
• It checks that the iOS firmware is properly signed using Apple’s Secure Enclave and SHSH (Signed Hash Blobs).
• If verification fails, the iPhone enters DFU Mode.
• If everything checks out, iBoot moves to load the iOS Kernel.

🔹 Stage 5: Kernel & System Initialization

The iOS operating system starts booting.

5️⃣ Kernel Execution Begins

• The iOS kernel is loaded from NAND storage into RAM.
• The XNU Kernel (Apple's hybrid UNIX-based kernel) is initialized.
• The kernel starts loading essential drivers for hardware components (Wi-Fi, Bluetooth, Touchscreen, etc.).
• The filesystem is checked for errors.
• If kernel loading fails, the iPhone may enter a boot loop.

6️⃣ Secure Enclave & Encryption Setup

• The Secure Enclave Processor (SEP) is activated.
• This subsystem is responsible for:
  • Encrypting & decrypting user data
  • Storing Face ID / Touch ID information
  • Protecting device security against hacking

7️⃣ Baseband Modem Initialization

• The Baseband Processor (BP) is activated.
• This allows the iPhone to connect to cellular networks (4G/5G, calls, SMS).
• If the baseband fails, the phone may show "No Service".

🔹 Stage 6: User Interface & Final System Load

Now that the system is running, it prepares for user interaction.

8️⃣ SpringBoard Loads (iOS Graphical Interface)

• SpringBoard (iOS's UI framework) loads the Home Screen.
• This includes animations, icons, widgets, and touch controls.

9️⃣ Background Services Start

• Wi-Fi, Bluetooth, AirDrop, and push notifications are activated.
• Apps begin to refresh data in the background.
• iCloud sync and backup services are restored.

🔟 Lock Screen or Home Screen Displayed

• If enabled, Face ID / Touch ID authentication is required.
• If authentication is successful, the Home Screen appears, completing the startup process!

🛠 Troubleshooting Boot Issues

If an iPhone fails to boot properly, it may get stuck at different stages:

1️⃣ Boot Loop (Apple Logo Stuck)

• Kernel panic or firmware corruption.
• Caused by failed updates, jailbreaks, or hardware issues.
• Fix: Use DFU Mode and restore via iTunes/Finder.

2️⃣ Recovery Mode (Connect to iTunes Logo)

• iBoot verification failed (corrupt firmware).
• Fix: Restore via iTunes using an official IPSW file.

3️⃣ DFU Mode (Black Screen, Recognized by iTunes/Finder)

• Deep firmware issue or baseband failure.
• Fix: Manually restore via IPSW or check for hardware problems.

4️⃣ Stuck on Apple Logo

• System crash during startup.
• Fix: Try a force restart (Volume Up → Volume Down → Hold Power Button).

🔑 Summary: Key Steps in iPhone Boot Process

This is the complete and detailed process of how an iPhone starts up! 🚀