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This lesson covers the maintenance of no-service and dial-up failures
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When the visual inspection finds that the components of the 2 g channel are not corroded by water,
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and the mainboard is very new and has not been touched, then we proceed to the next step
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If it is not received, how to repair it? At this time, it is necessary to measu
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To receive the power supply of the chip, we need to insert different cards according to your
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The mobile card looks for the receiving chip that g s m 900 passes through,
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and the Unicom card mainly checks the receiving chip that g s m 1,800 leads to
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For Telecom calls, we mainly look for the receiving chip that it leads to in the B26 frequency band.
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The receiving chip is called LNA in the drawings
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Measure whether the power supply of the receiving chip is normal
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Find the power supply pins
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If the power supply of the receiving chip cannot measure the voltage,
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you need to measure the diode value of the receiving chip to ground
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Of course, you should pay attention when measuring the voltage.
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It is necessary to turn on the phone, and it is best to insert the number card on the main board of the mobile phone.
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Measure the ground value of the receiving chip if there is no problem, but no voltage can be measured
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At this time, if the ground value is not abnormally low, it is necessary to re-solder the chips that provide the receiving power supply
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Find this chip, the chip should be resoldered first
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After re-soldering, if the power-on measurement still has no reception,
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it is necessary to replace the chip that provides the receiving power supply
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But if the reception is normal, we will go to the next step
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Launch anomaly maintenance
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When there is no abnormality in the reception, it means that there is no service caused by the failure of the transmitting circuit.
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The next step is to measure the power supply of the 2 g channel power amplifier
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What you must know about 2G channels is that China Mobile mainly looks at GSM900; China Unicom mainly looks at GSM 1,800
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The power amplifier of Mobile Unicom is generally called g s m power amplifier or 2 g power amplifier
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Or the transmitted power amplifiers of these two frequency bands
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Telecom mainly looks at the power amplifier it passes through in the B26 frequency band
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So what we are talking about here is the power amplifier, and the above is the power supply of the power amplifier.
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After we find the power amplifier first, you can test which chip the power supply of the power amplifier comes from.
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Insert the card in the mobile phone, turn on the mobile phone, and find the chip that provides power to the power amplifier
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Measure whether the power supply output of the power amplifier has a voltage above 1.8 volts
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Of course, some power amplifiers are clearly marked with a power supply voltage, some may have 3 volts, and some may have 1.8 volts.
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If it is a model with independent power amplifier power supply, it can output power from one power amplifier or two power amplifiers.
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Then this can short-circuit the input and output
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Power on again to test the signal, and the general fault can be repaired
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Of course, if it is a power amplifier chip that can output multiple power supplies, the short circuit method is not suitable at this time.
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At this time, it is best to directly replace the power supply chip of the power amplifier, and the general fault can be repaired
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That's all for this lesson