আজকের ক্লাস: Redmi A3X এ No Service / Searching / Radio Off এলে network section এ কোথায় কী চেক করবেন — diagram দেখে step by step।
Diagram 1 — RF power rails (এখানে আগে মাপুন)
Board খুলে RF area খুঁজুন। Colored lines দেখে এই rails চেক করুন: VDDDCXO, VDDRF_1V25, VDDRF_1V8, VDDMEM। Voltage না থাকলে আগে PMIC/rail ঠিক করুন — IC replace নয়।
Diagram 2 — XO / extra RF supplies
এখানে VDDDIG_XO, আরও RF 1.8V লাইন, VDD1V85। Clock/XO supply মিস হলে baseband/network search fail হয়।
Diagram 3 — PA / antenna path
VBAT ও VDDWPA PA তে যাচ্ছে কিনা দেখুন। 2G/4G call drop বা TX weak হলে এই path + PA area।
Diagram 4 — RFFE / WTR ways
RFFE CLK ও RFFE DATA, VAPT_PA, WTR band lines। Searching but no register → প্রায়ই RFFE/RF IC এখানে।
Teacher steps (কোন অর্ডারে কাজ করবেন)
- Symptom confirm: *#*#4636#*#* → Radio Power ON/OFF; Settings এ network search।
- Cool test (ফোন অফ / battery disconnect): Diode mode — GND red probe; rails ও RFFE pins এ OL না কি short।
- Hot test (ফোন অন): Voltage mode — VDDRF 1.8 / 1.25, VDD1V85, VBAT on PA, RFFE lines এ pulse/1.8V।
- Decision: Rail missing → follow supply back to PMIC. Rails OK কিন্তু RFFE dead → RF/PA IC বা line repair।
- Microscope এ pad মিলিয়ে diagram এর রঙিন লাইন follow করুন — wrong pad এ jumper দেবেন না।
Basic Hardware
Must Read
Teacher guide: measure RF rails first (Diagram 1–2), then PA/antenna (Diagram 3), then RFFE/WTR (Diagram 4). Always cool-test diode before hot voltage.
Common Faults
No Service, Searching for Network, Radio Off, Emergency Calls Only, Weak Signal
Main Function
RF power rails, PA path, RFFE CLK/DATA & WTR ways
Hot Test Report
Phone ON, battery connected (careful). VDDRF_1V8 ≈ 1.8V on marked caps; VDDRF_1V25 ≈ 1.25V; VDD1V85 ≈ 1.85V; VBAT/VDDWPA on PA ≈ battery (≈3.7–4.2V); RFFE CLK/DATA ≈ 1.8V with activity when searching network; VAPT_PA may vary with TX (often ~0.5–3.4V range on APT designs).
Cool Test Report
Phone OFF, battery removed. Diode mode (black on GND typical shop habit — note your meter polarity). RF rail caps: expect mid hundreds of mV diode drop, not 0.000 short and not OL. RFFE CLK/DATA pins: similar healthy diode range (~0.4–0.65V class). GND pads beep. Short to ground on 1.8V rail = find shorted cap/IC before power-on.
Details
Match colored lines on Diagram 1–4 under microscope. Start at RF rail capacitors near transceiver, then PA VBAT/VDDWPA, then RFFE CLK/DATA to WTR.
Hardware Solution
IC model: Redmi A3X Network / RF Section
Problems and Solution
Step 1: Confirm Radio Power and symptom (No Service / Searching).
Step 2: Open board, find RF section matching Diagram 1–4.
Step 3: COOL TEST diode on VDDRF rails + RFFE CLK/DATA (no short/OL).
Step 4: HOT TEST voltage on same points with phone ON.
Step 5: If rail missing → chase PMIC/supply path. If rails OK → check PA (Diagram 3) then RFFE/WTR (Diagram 4).
Step 6: Replace/reball only after rails and lines verified.