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Samsung Galaxy S21 SM-G991
Q&A
User questions and answers about Samsung Galaxy S21 SM-G991
- tips, troubleshooting, and real experiences from the community.
Question 🤔
00
REPO
2026-10-20
I recently replaced the screen on my Samsung Galaxy S21 5G with a replacement OLED display. After the repair, I experienced several issues:
1. Mobile network: Both my physical SIM and eSIM showed “Emergency calls only.” The technician later discovered that a flex cable was missing and replaced it. Mobile network service has since been restored.
2. Wi-Fi reception: The Wi-Fi range has significantly decreased. The phone connects near the router, but when I move farther away, it repeatedly disconnects and sometimes loses the connection. Another phone maintains a stable connection in the same location.
3. Bluetooth: Bluetooth range appears normal.
The technician has inspected the phone but has not identified the cause. I compared the internal layout with a disassembly video for the same model, but I could not identify any obviously missing components.
My questions:
- Which Wi-Fi antenna, coaxial cable, flex cable, or contact points should be inspected on the SM-G991U?
- Could an incorrectly seated antenna contact, missing screw, damaged connector, or improperly fitted internal cover cause this reduced Wi-Fi range?
- What diagnostic tests would help distinguish an antenna connection problem from a Wi-Fi IC or other motherboard fault?
I would appreciate guidance on the most likely causes and the appropriate diagnostic steps before replacing any additional components.
Hi, You should carefully check all the connectors on the motherboard and the bottom board, as well as on all the flex cables, to ensure they aren’t damaged or bent. More importantly, non-original display modules often come with a non-original frame. In an original frame, the antenna contacts - which are integrated into the frame itself - consist of gold-plated pads. In a non-original frame, however, these are often just pieces of yellow foil stuck on with adhesive. As a result, the contact is either completely missing or insufficient, which leads to poor signal quality and a reduced signal range. - the Wi-Fi antenna, which attaches to the frame (near vibration motor); all screws must be tightened, and the contact pads on the frame must be free of any oxidation. Naturally, the flex cable itself must also be undamaged. Photo: - These are the gold-plated contacts for cellular connectivity.
Issue: Significantly reduced Wi-Fi range after screen replacement
I recently replaced the screen on my Samsung Galaxy S21 5G with a replacement OLED display. After the repair, I experienced several issues:
1. Mobile network: Both my physical SIM and eSIM showed “Emergency calls only.” The technician later discovered that a flex cable was missing and replaced it. Mobile network service has since been restored.
2. Wi-Fi reception: The Wi-Fi range has significantly decreased. The phone connects near the router, but when I move farther away, it repeatedly disconnects and sometimes loses the connection. Another phone maintains a stable connection in the same location.
3. Bluetooth: Bluetooth range appears normal.
The technician has inspected the phone but has not identified the cause. I compared the internal layout with a disassembly video for the same model, but I could not identify any obviously missing components.
My questions:
- Which Wi-Fi antenna, coaxial cable, flex cable, or contact points should be inspected on the SM-G991U?
- Could an incorrectly seated antenna contact, missing screw, damaged connector, or improperly fitted internal cover cause this reduced Wi-Fi range?
- What diagnostic tests would help distinguish an antenna connection problem from a Wi-Fi IC or other motherboard fault?
I would appreciate guidance on the most likely causes and the appropriate diagnostic steps before replacing any additional components.
Hi, I believe I already answered that. You should carefully check all the connectors on the motherboard and the bottom board, as well as on all the flex cables, to ensure they aren’t damaged or bent. Photo: - This is the Wi-Fi antenna, which attaches to the frame; all screws must be tightened, and the contact pads on the frame must be free of any oxidation. Naturally, the flex cable itself must also be undamaged.
REPO
2026-10-20REPO
2026-10-20