Asus P735, Service Manual

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Lv3Lv4 Repair Manual
- 53 - ASUS Proprietary
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21. GSM & WCDMA RF Tx/Rx Path
How RF signal is transmitted and received between components on P735 PCB is
explained in this section. It is important to realize RF transmission path (Tx) and
receiving path (Rx) before starting out to repair NG PCB, because engineers need to
choose proper test points which assist us to distinguish where the problem is. The
following paragraphs describe both Tx and Rx path in GSM and WCDMA bands. The
related test points are listed in previous section.
21.1 GSM Tx path
Transceiver, RF6001 (U900), receives IQ signals coming from baseband, and
output signals of RF6001 Pin22 and Pin23 are transmitted into the buffer of receiver,
RF2722. Then RF2722 Pin12 and Pin13 emit the low band signal (GSM900) and high
band signals (DCS1800 or PCS1900) separately.
In the low band, output signal from RF2722 Pin12 passes through C917,
attenuator (U903) and RF3166 (U904) Pin7, power amplifier, sequentially.
Transmission and receiving switch (U902), also named T/R switch, gets the amplified
signal from RF3166 Pin23 via matching circuits. RF signal coming from T/R switch
Pin12 is transmitted to connector (Con850) and radiated via the GSM antenna of
P735.
In the high band, output signal from RF2722 Pin13 passes through C934,
attenuator (U905) and RF3166 (U904) Pin1, power amplifier, sequentially.
Transmission and receiving switch (U902), also named T/R switch, gets the amplified
signal from RF3166 Pin30 via matching circuits. RF signal coming from T/R switch
Pin10 is transmitted to connector (Con850) and radiated via the GSM antenna of
P735.
21.2 GSM Rx path
RF signals, receiving from base station via the GSM antenna, pass through
connector (Con850) and T/R switch Pin6 (U902) sequentially. There are three output
pins of T/R switch, including Pin1, Pin14, and Pin15. The output path which RF signal
is transmitted depends on band selection of T/R switch.
In GSM900 band, the receiving signal which is transmitted from T/R switch Pin1
passes through SAW filter (BPF1) and matching circuits sequentially. Upon RF2722
(U901) receiving the signal, it is amplified in the Low Noise Amplifier (LNA) of the