I have five Optimus L90 D415 phones for my family. My phone quit working on the T-Mobile network, although the wi-fi connection still worked for Internet usage only. No calls or texts could be sent or received, even with wi-fi calling enabled. The signal strength indicator was missing from the display. In Settings>About Phone>Network, Network was unknown, signal strength was zero, Service state was "out of service", and Mobile Network state was "Disconnected". In Settings>About Phone>Status, my phone number was unknown, IMEI was unknown, and IMEI software version was unknown.
T-Mobile said I needed a new SIM card. Got one, no help. That was the best they could do. After that, they said I needed a new phone, despite this one being only a few months old with no damage.
I took one of the other phones that was no longer in use, but still worked. The only fault was a cracked screen. First thing I did was to swap out the motherboard. This did not help, the fault stayed with the phone. Next, I swapped out the antenna cable that delivered cellular signal to the motherboard. No help. Finally, I swapped out the charger dock flex board. This board is on the other end of the antenna cable. This fixed the problem. This board does nothing more for the signal than provide a connection for the cellular antenna built into the rear frame, but there are also some very small components on the board (probably 3 caps and an inductor) mounted in the antenna circuit. My guess is that one or more of the caps went defective.
The charger dock board for the D410 and D415 is available on eBay for about $6. It is easy to replace. Find a disassembly video on YouTube, and remove only the silver rear frame, which exposes the motherboard and the charger dock board. Disconnect three connectors used by the charger dock board (two on the right, one of which is the antenna cable, and one in the center), then use a flat pry tool to remove it. Slide the pry tool underneath the antenna connector, and wiggle it back and forth to loosen the adhesive that holds the board in place. Once that side of the board is loose, slide the pry tool underneath the dock connector, and work the center of the board loose. Next, work the pry tool toward the opposite edge. Remove the defective board, and replace with a new part.
T-Mobile said I needed a new SIM card. Got one, no help. That was the best they could do. After that, they said I needed a new phone, despite this one being only a few months old with no damage.
I took one of the other phones that was no longer in use, but still worked. The only fault was a cracked screen. First thing I did was to swap out the motherboard. This did not help, the fault stayed with the phone. Next, I swapped out the antenna cable that delivered cellular signal to the motherboard. No help. Finally, I swapped out the charger dock flex board. This board is on the other end of the antenna cable. This fixed the problem. This board does nothing more for the signal than provide a connection for the cellular antenna built into the rear frame, but there are also some very small components on the board (probably 3 caps and an inductor) mounted in the antenna circuit. My guess is that one or more of the caps went defective.
The charger dock board for the D410 and D415 is available on eBay for about $6. It is easy to replace. Find a disassembly video on YouTube, and remove only the silver rear frame, which exposes the motherboard and the charger dock board. Disconnect three connectors used by the charger dock board (two on the right, one of which is the antenna cable, and one in the center), then use a flat pry tool to remove it. Slide the pry tool underneath the antenna connector, and wiggle it back and forth to loosen the adhesive that holds the board in place. Once that side of the board is loose, slide the pry tool underneath the dock connector, and work the center of the board loose. Next, work the pry tool toward the opposite edge. Remove the defective board, and replace with a new part.
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