Lenovo S930 Manual de serviço - Página 26

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LENOVO S930 Cellphone Service Manual

4.2.4 Power output related problems

⚫

Problem: The device can turn on and receive signals normally. But there's no power output or

power output is very low, when it is trying to output power of double frequency bands or single

frequency band.

⚫

Reason: Many factors can cause no or low power output, such as when Transceiver output circuit,

PA module input/output circuit, antenna connectors and antenna switch control signals or power

feeding circuits have a problem. In particular:

◼

RF connector (CON2101)

Check whether connections between RF connector CON2101 and test probes of RF test

cable are reliable; patches are fixed in the correct direction; or antenna connectors

are damaged.

Solution: Replace antenna connectors and ensure patches are in the correct

direction.

◼

RF power amplifier (U2102)

Whether PA's control signal PA_ENABLE (Pin17) is at high level (about

A．

2.8V); If it is at low level, PA will have no output;

PA's power feeding pins Pin13, pin14; check whether power feeding voltage falls

B．

into normal range (normally 3.6V～4.2V);

Check whether PA's RF input

C．

problems;

Whether PA's RF input R2115 and C2131 have dry joint problems;

D．

PA's V_ramp control signal circuit: If C2111, R2111 and R2112 have dry joint

E．

or circuit break problems, PA's output power will be abnormal.

◼

Transceiver (U2101)

Check whether power feeding voltage of Transceiver (U2101) falls into the normal

A．

range. You can check power feeding voltage at the place where power feeding

filter capacitor and U2101 are connected. Then check whether peripheral

circuits have dry joint problems.

Whether dry joint or short circuit problems exist on Transceiver (U2101) and its RF

B．

output matching circuits.

If it's permitted by whole-unit service terms and conditions, you can put the cell

phone into constant-emission status of maximum power. Then detect power output of each

module in the emission channel with probes from a spectrum analyzer. In normal

circumstances,

A．

you can detect a power output about GSM 33dBm or DCS/PCS 30dBm at the output

end of the RF connector;

B．

you can detect a power output about 32dBm or 29dBm at the place where PA output

end pin26 is connected;

C．

C2101

R2102

C2102

Page 26

have dry joint

and

R2105