Lenovo P70-A Руководство по эксплуатации - Страница 29

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Repair Manual of Lenovo P70-A Mobile Phone

Excessive Phase Error

Check the power supply part of PA（and transceiver

Replace the elements in

solder joint

4.12.4 Power output problems

Fault: Normally power-on and receive, but when outputting two frequency bands or single

frequency band power, there is no input power or the input power is very low.

Cause: There are many reasons for no output power or very low power, which may be the

results of faults of Transceiver output part, PA input and output circuit, antenna connector

and antenna switch control signal or power supply circuit. Specific circumstances are:

RF connector（J1001/J1002）

Checking: Whether RF connector J1001/J1002 and the test probe of RF test cable are

well connected or the patch is oppositely pasted or the antenna connector is damaged.

Shooting: Replace antenna connector and ensure right direction of patch.

RF power amplifier (PA)

A. Whether the control signal of PA(U901,U902) is high level (about 2.8V); if it is low

level, there is no output of PA;

B. Check the PA power supply part to see whether the power supply voltage is in the

normal range (typically 3.6V ~ 4.2V);

C. Whether the RF input parts of PA are in cold solder joint;

D. Whether the RF output parts of PA is in cold solder joint;

E. Part circuit of VPA_PMU control signal of PA: if it is in old solder joint or in interruption

of circuit, PA also has no output power.

Transceiver（U801）

A. Whether the power supply voltage of Transceiver（U801） is within normal range;

check the power supply voltage between power supply filtration capacitor and U801

connection and then check whether the surrounding circuit is in cold solder joint.

B. Whether there is cold solder joint or short circuit in Transceiver （U801）.

cold