2 receiver circuit power supply is normal . Such as low -noise RF amplifier tubes , Mixers , IF amplification bias voltage is normal , power receiving local oscillator circuit is normal and so on .

    3 transmitter circuit power supply is normal . If the transmitter power of the oscillator circuit (TXVCO), power amplifier, power control circuits are normal.

    4 power supply integrated circuit is normal . Integrated circuits used in mobile phone features and more, has been modularized. Different modules perform different functions , and different modules providing different require external operating voltage , the power supply to check the overall chip . If powered Motorola V998 IF IC (U913) have several groups of power .

    Note that many mobile radio circuit voltage are controlled , and some by the band selection control signal , and some control signals TX-0N RXON or by some number of simultaneously controlled by the control signal . In other words, these controlled voltage is not output when not needed (such as the supply voltage transmission circuit is in standby mode undetectable ) . Further, when the control signal is a pulse signal (e.g., RXON, TXON , etc. ) , the output voltage is a pulse voltage , when the voltage measured with a multimeter , much smaller than the nominal value.

Third, the current method

    Current method is the most commonly used mobile phone repair a way to repair those experienced by observing the current work under different working conditions , to determine the approximate site of the fault. Therefore , mobile phone repair personnel should have included a multi-purpose power supply current, voltage meter on hand , use easy maintenance. Here are several common normal operating current of the phone, reference for maintenance.

    A Nokia 3210 mobile phone , after connecting the power supply, when you press the power button , ammeter rise to 50mA, rose to more than 100 mA and then rose to 200mA, suddenly rose to 300, ~ 400mA swing back and forth at this time find the phone network , when it finds the network, then back to 150-180mA ammeter swing back and forth , when the backlight is off, then back at 10mA swing . In the current changes in , 50mA supply current description part in the work , more than 100 mA Description clock circuit has been working , when more than 200 mA is receiving circuit at work , 300 ~, 400mA is received , the transmitter at work and looking for a network . 150-180mA explanation has been found , but the network is in standby mode background lights. 10mA standby state after the backlight turns off . A 3210 phone after pressing the power button , if we see the current changes above , the phone should not be any problem.

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