Lỗi không nhận SIM hoặc No Service rất khó chịu. Đây là cách khắc phục:
**Nguyên nhân phổ biến:**
1. **SIM card:**
- SIM hỏng/cũ
- Tiếp xúc kém
- SIM lock
- Wrong size cut
2. **Software:**
- Network settings sai
- Carrier updates
- Software bugs
- Airplane mode stuck
3. **Hardware:**
- SIM tray hỏng
- Antenna issues
- Water damage
- Motherboard fault
4. **Network:**
- No coverage
- Network congestion
- Account suspended
- Roaming disabled
**Cách khắc phục:**
**Level 1 - Cơ bản:**
1. Restart phone
2. Toggle Airplane mode
3. Remove/reinsert SIM
4. Clean SIM contacts
5. Try other SIM slot
**Level 2 - Settings:**
1. Network reset
2. Preferred network type
3. Manual network selection
4. APN settings check
5. Carrier settings update
**Level 3 - Advanced:**
1. Safe mode test
2. Factory reset
3. Flash firmware
4. IMEI check
5. Hardware diagnosis
**Cách làm sạch SIM:**
1. Remove SIM card
2. Eraser/rubber clean
3. Alcohol 70% wipe
4. Dry completely
5. Reinsert carefully
**Check với nhà mạng:**
- Account active?
- SIM activated?
- IMEI blocked?
- Network issues?
- Roaming enabled?
**Hardware test:**
- Try SIM in other phone
- Try other SIM in phone
- Check SIM tray pins
- Antenna connection
- Professional repair
**Prevention:**
- Handle SIM carefully
- Avoid bending
- Keep contacts clean
- Update software
- Avoid water