Grogu, when I dial *#899# and enter the engineer mode of my smartphone, under manual test-device debugging, when I click on 'small board matches main board' option, it shows failed, why, does that means the technician has swapped some hardware like main board or daughter board?
Hello Shikhar,
Thanks for sharing this detail—it's a sharp observation, and diving into Engineer Mode like this is a great way to get concrete data on your device's hardware integrity. I can see why a "Failed" result on the "Small board matches main board" test would raise alarms, especially with your ongoing concerns about the August repair. I'll explain this factually based on Realme's service documentation, Engineer Mode breakdowns from forums like XDA Developers and Realme Community, and hardware insights from teardowns (e.g., GSMArena for the Realme 3 Pro). The tl;dr:
A "Failed" here doesn't definitively prove a hardware swap (like the main board/motherboard or daughter/small board), but it does indicate a potential mismatch or issue that could stem from the repair. It's worth investigating further, but let's break it down step by step without jumping to conclusions.
What Does "Small Board Matches Main Board" Test Mean in Engineer Mode?
On Realme devices like your 3 Pro (Snapdragon 710, Android 11/Realme UI 2.0), Engineer Mode (*#899#) is a diagnostic tool for technicians to test hardware components. Under Manual Test > Device Debugging:
- Main Board: This refers to the primary motherboard (logic board), which houses the CPU, RAM, storage, modem, and main sensors.
- Small Board: Often called the daughterboard or sub-board, it's a smaller secondary board connected to the main one via cables/flex connectors. On the Realme 3 Pro, it typically includes components like the USB charging port, microphone, speaker (relevant to your "sound issue"), vibration motor, and sometimes antennas or SIM tray interfaces.
- The Test Itself: "Small board matches main board" checks for compatibility and connection integrity between these two boards. It verifies things like serial numbers, firmware versions, electrical signals, or calibration data to ensure they're synced and functioning as a unit. A "Pass" means everything aligns as expected from the factory; a "Failed" flags a discrepancy.
This test is common in Oppo/Realme service modes (inherited from their MTK/Qualcomm tooling) and is used during repairs to confirm if replaced parts integrate properly.
Why Is It Showing "Failed" on Your Device?
A failure doesn't automatically mean tampering or a full swap—it's often benign or repair-related. Based on user reports and service guides, common reasons include:
- Repair-Related Issues (Most Likely in Your Case):
- Loose or Faulty Connections: During the sound issue fix (which might have involved the speaker/microphone on the small board), the technician could have disconnected/reconnected flex cables between the boards. If not seated perfectly, it causes a mismatch signal—leading to "Failed."
- Component Replacement: If they swapped just the small board (or parts on it, like the charging port or speaker), the new one might have a slight firmware mismatch or need recalibration. Realme parts aren't always 100% identical, and this test can flag that.
- Calibration Drift: Physical handling (e.g., opening the phone) can affect sensor alignments, which this test indirectly checks.
- Software or Firmware Glitches:
- Outdated Firmware: Android 11 updates or Realme UI patches can sometimes cause false failures if the boards' embedded software doesn't sync perfectly.
- Cache/Corruption: System cache buildup or minor OS errors (e.g., from reboots during repair) might trigger this without hardware changes.
- Hardware Degradation: Over time (your phone is from 2019), wear on connectors or components could lead to failures, unrelated to the repair.
- Could It Indicate a Full Swap? Possibly, but less likely:
- If the technician swapped the main board or small board entirely (e.g., with non-original parts), this test would fail due to mismatched IDs or incompatibilities. However, as we discussed before, a full main board swap would typically require a factory reset or show bigger issues (like data loss), which hasn't happened.
- It's not a "smoking gun" for tampering—many users report this failure after legitimate repairs or even on untouched devices. For instance, XDA threads on Realme/Oppo phones note it as a common post-repair quirk that resolves with reconnection or firmware flashes.
Importantly, if a swap occurred, you'd likely see other symptoms (e.g., IMEI changes, boot issues, or failures in other Engineer Mode tests like sensors or modem). Since your phone is otherwise functional, this is more indicative of sloppy repair work than malicious swapping.
How to Investigate and Fix This
To get clarity and potentially resolve it:
- Run Related Tests: In Engineer Mode, check other Manual Test sections (e.g., Charging, Audio, Sensors). If they pass but this one fails, it points to a specific board connection issue.
- Reboot and Retest: Exit Engineer Mode, restart the phone, and re-enter *#899# to test again—sometimes it's a temporary glitch.
- Hardware Inspection: If comfortable, power off, remove the back cover (use guides from iFixit), and visually check for loose cables or obvious swaps (e.g., different board colors/markings). Otherwise, take it to a trusted shop.
- Firmware Update or Reset: Check for system updates (Settings > About Phone > System Updates). If needed, clear cache partition via recovery mode (Volume Down + Power > Wipe cache). A factory reset is a last resort but would recalibrate everything.
- Professional Verification: Visit an official Realme service center—show them the test result and repair history. They can run full diagnostics, confirm board authenticity (via serial numbers), and fix any mismatches (e.g., by reseating connectors or flashing firmware). This is your best bet to rule out swaps.
- Log Check: Generate a bug report (Developer Options > Take bug report) and search for "board" or "mismatch" entries—look for timestamps around August.
This "Failed" result aligns with a post-repair hiccup (e.g., from fixing the sound issue) rather than a covert swap, especially since it ties into components like audio. It doesn't contradict our earlier discussions—tampering remains unlikely, but getting that pro check will give you peace of mind. If you test more in Engineer Mode or notice other failures, let me know the details, and we'll analyze them. You're closing in on the full picture—keep going!
Best regards,
Grogu