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🛠 Difficulty: 🟢⚪️⚪️
⏰️ Repair Time: 40 minutes
A Samsung S21 FE came in for repair with a weak network signal issue. The phone struggles to find a 4G connection, and callers often can’t reach the user.
Here’s what the problem looks like: the signal level constantly jumps around, and it almost never connects to 4G.
We begin by removing the back cover and disassembling the phone.
This model is equipped with the problematic QPM6815 signal amplifier, which frequently fails on its own.
So my first thought was that it could be the culprit.
But of course, we also need to check another common issue found in Samsung smartphones: weak or faulty connectors.
Starting from the S21 series and onward, Samsung switched from coaxial cables to flat flex cables for transmitting antenna signals.
This change introduced a new issue—broken inter-board connectors affecting network performance 🙃
The top section of the motherboard looks fine.
So we move on to disassemble the lower section and inspect the connectors on the sub-board.
And here it’s immediately clear—the connector on the inter-board flex cable is broken, and so is the corresponding connector on the sub-board.
This simplifies the repair. We prepare replacement flex cables and new connectors for installation.
Using a soldering station, we replace the damaged connectors with new ones.
We clean the flux off the connectors.
We reconnect the sub-board and the inter-board flex cable inside the housing to test functionality.
We power on the phone with a SIM card inserted and check signal strength across all network bands.
The phone now works correctly in all modes—full signal strength, and calls go through without any issues 👌
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