Boot sequence for many Qualcomm/MTK phones:

1. PMIC sends power rails
2. CPU starts CLK
3. CPU loads BootROM
4. CPU accesses eMMC/UFS
5. Reads bootloader
6. Enters Android kernel

You can capture:

• Power-ON trigger (PWRKEY)
• Xtal_CLK / SYS_CLK activation
• eMMC activity right after boot
• Reset timings

If any step is missing, you find the fault.

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3️⃣ Check Touch/Display/Camera I2C/SPI Lines

Using protocol decode:

Check I2C:

• SDA
• SCL

If display not working:

✔ Check if CPU is querying the display IC
✔ Check ACK responses
✔ Check touch panel communication
✔ Diagnose missing pull-up resistors

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4️⃣ Detect Fake / Dead Chips

Sometimes replacement ICs are:

• Fake
• Not initialising
• Wrong firmware
• Bad soldering

Logic analyzer shows:

❌ No handshake
❌ No start condition
❌ Stuck at logic 0
✔ Correct signal timing if the chip is original

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5️⃣ Check SD Card / ISP / JTAG Lines

When recovering data or checking ISP points:

• CE (Chip Enable)
• CLE (Command Latch Enable)
• ALE (Address Latch Enable)
• WE / RE
• R/B
• Data0–7

You can:

✔ Confirm NAND IC is alive
✔ Confirm commands are sent
✔ Check if WE/RE toggling is normal
✔ Detect line short or open track
✔ Validate timing for data recovery operations

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6️⃣ Find Broken Tracks / Cold Solder Lines

If a line is not transmitting:

• It will remain always HIGH (pull-up only)
• Or LOW (short to ground)
• Or random unstable (partial broken track)

The logic analyzer makes it visible instantly.

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7️⃣ Compare Good Board vs Faulty Board

Capture the same signals on a:

✔ Working motherboard
✔ Faulty motherboard

Then compare waveforms to identify:

• Missing clock
• Missing commands
• Wrong timing
• Dead peripheral
• Shorted line
• Corrupted data transfer

This is a very powerful technique.

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📌 Real Example: Phone Not Booting After Reballing

If the CPU reballing was bad:

• CLK will appear delayed or unstable
• Data lines glitching
• CMD not transitioning properly
• All lines stuck HIGH (bad ground)
• All lines stuck LOW (short)

One 5-second capture can confirm whether reballing was successful.

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📌 Real Example: Phone Stuck on Logo

Logic analyzer helps check:

• Does eMMC keep responding?
• Does CPU load further partitions?
• Do read commands suddenly stop? (bad sector)
• Does one data line drop? (bad ball)

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🔧 Required Equipment

To use it properly:

Recommended logic analyzers:

• DSLogic Plus 100/200/400 MHz
• Saleae Logic Pro 8/16
• LAP-C series

Probes:

• Fine-tip probes
• Ground spring probes
• Clean test pads
• ESD precautions

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📘 Summary (Easy to Remember)

Issue	What Logic Analyzer Shows
No Boot	Missing CLK / CMD
Dead eMMC	CMD active but DATA dead
Bad Reball	Glitches, unstable timing
Broken Track	Line stuck HIGH/LOW
I2C Fault	No ACK from peripheral
Fake IC	No handshake signals
Boot Loop	Repeated command sequence

✅ How Useful Is a 24 MHz Logic Analyzer for Mobile Repair?

✔ Good for Slow & Medium-Speed Digital Signals

A 24 MHz analyzer is suitable for signals up to 4–8 MHz reliably (rule: sample ≥ 3–4× signal).
So 24 MHz LA is OK for:

Supported Tasks (Useful):

• ✔ I2C lines (100 kHz / 400 kHz / 1 MHz)
• ✔ SPI lines up to 5–6 MHz
• ✔ UART/Debug (115 k–3 M baud)
• ✔ Buttons / PWRKEY logic
• ✔ Reset lines
• ✔ Touch screen I2C
• ✔ Sensors (gyro, proximity, etc.)
• ✔ Fingerprint SPI
• ✔ Small EEPROM communication

Meaning:
A 24 MHz logic analyzer is very useful for display, touch, sensors, buttons, and communication faults.

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❌ Where 24 MHz Is NOT Useful

Mobile phones use high-speed buses, and 24 MHz is too slow to view them.

Here is what a 24 MHz LA cannot correctly capture:

Not Supported (Too Fast):

1️⃣ eMMC Signals

• eMMC CLK: 26 MHz, 52 MHz, 200 MHz
  ❌ 24 MHz cannot decode CMD/DATA
  ❌ you will see garbage or flat lines

2️⃣ UFS Signals

• UniPro high-speed lanes: 500 MHz–1.5 GHz
  ❌ Completely impossible
  Even 500 MHz analyzers cannot decode UFS.

3️⃣ DDR / LPDDR RAM

• Frequencies: 400–1600 MHz
  ❌ No chance

4️⃣ High-speed Display (MIPI DSI)

• 1–1.5 Gbps per lane
  ❌ Not possible
  Use an oscilloscope instead (for clock presence only).

5️⃣ High-speed Cameras (MIPI CSI)

• Too fast for any logic analyzer under 500 MHz

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📌 Simple Summary (Remember This)

Signal	Frequency	24 MHz LA	Useful?
UART	<3 MHz	✔ Yes	Excellent
I2C	100 k–1 MHz	✔ Yes	Very good
SPI	1–5 MHz	✔ Yes	Good
eMMC	26–200 MHz	❌ No	Not usable
UFS	500 MHz–1.5 GHz	❌ No	Impossible
MIPI display	>1 GHz	❌ No	Impossible
MIPI camera	>1 GHz	❌ No	Impossible

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💡 Practical Real-Life Examples (Mobile Repair)

✔ You can diagnose:

• Touch not responding → Check I2C ACK
• Fingerprint “not detected” → Check SPI lines
• No display backlight → Check enable/INT signals
• Power key not working → Check logic level
• Sensor not working → Check communication
• Charging IC communication with CPU (I2C)

❌ You cannot diagnose:

• No boot due to eMMC
• UFS corruption
• CPU-to-eMMC signal timing
• Bootloader read sequence
• DDR RAM problems

These need 200–400 MHz models like DSLogic Plus / Saleae Pro.

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⭐ Final Verdict

✔ A 24 MHz logic analyzer is useful for:

• Sensor lines
• Touch/display control
• Button logic
• Charging IC communication
• Small peripheral IC debugging

❌ But it is not useful for:

• eMMC trouble-shooting
• Dead boot issues
• UFS-based phones
• High-speed CPU communication