Mobile phone common fault repair （2）

Ananda Technical department   

No power failure

(1) press the power button can not boot. If the current is too small, the fault location is generally in the clock circuit and flash rom and ram and other logic / audio part, if the current is too large, the fault location is generally in the Send the power amplifier and power supply part, and sometimes due to power supply filter capacitor leakage caused.


(2) press the power button to boot, but the current jump to the maximum, indicating that the clock and logic / audio and power supply part of the normal work, the fault comes from the RF processing circuit to receive and send access.


(3) If you press the power button to boot, release the power button to shut down; or delay about ten seconds or tens of seconds and shut down, the former more common in Ericsson models, Ericsson models boot process and logical work has nothing to do, and Shutdown process requires a logical part of the support, this phenomenon is a logical part of the fault. Usually eprom and cpu serial line open circuit, a / d converter power supply failure. The latter fault is called delay shutdown failure, multi and low voltage alarm, display black or no display and current is too large, the transmission channel power amplifier damage, circuit leakage and other failures occur at the same time.


(4) press the power button after the boot, but can not boot or crash at the same time, display characters and buttons can not work. This failure comes from the power control part of the desoldering software caused by the operation is not normal.

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Display failure

After the boot, the display appears without a character display, black screen, the fault occurs to adjust the contrast display of the negative pressure generator, display part of the integrated processing data cable, cpu data cable, connection socket, or display is damaged. For Ericsson models, turn on the moment to observe the display contrast control voltage changes, you can determine the working status of the cpu, because the contrast control voltage is provided by the cpu variable duty cycle after a group of pulses obtained by rectification.

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