LG YD2750 Service Manual

Features of Mobile Subscriber Radio Handset
(LG-YD2750 Type)

1. Wave Type

• G7W

2. Frequency Scope

• Transmit Frequency : 824.820 ~ 848.190MHz

• Receive Frequency : 869.820 ~ 893.190MHz

3. Rated Output Power

• 0.282W(24.5dBm)

4. Output Conversion Method :

5. Voltage and Current Value of Termination Part Amplifier(Catalogue included)

This is possible by correcting the key boaID channel.

Mode Type Name Voltage Current Power

CDMA FC7113 3.7V 600mA 0.32W

6. Functions of Major Semi-Conductors

Classification Function

MSM6000-208Pin-FBGA Operation control and digital signal processing of the mobile station

FLASH MEMORY

(K8D3216UTC-TI07)

STATIC RAM

(K1S161611A-FI70)

RFT6122 & RFR6122 Converting baseband signal into Tx RF signal and Rx RF signal

7. Frequency Stability

• ±0.5PPM

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Flash Memory (32Mbit) ▶ Storing of the mobile station operation
program

SRAM (16Mbit) ▶ Temporary storing of the data created while
busy

into baseband signal

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CDMA MOBILE SUBSCRIBER UNIT

LG-YD2750

SERVICE MANUAL

SINGLE BAND

CDMA MOBILE PHONE

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LG-YD2750

Table of Contents

General Introduction

............................................................................................................................................... 2

CHAPTER 1. System Introduction

1. System Introduction ................................................................................................................ 3

2. Features and Advantages of CDMA Mobile Phone .................................................................. 5

3. Structure and Functions of CDMA Mobile Phone ................................................................... 8

4. Specification .............................................................................................................................. 9

5. Installation ............................................................................................................................... 12

CHAPTER 2. NAM Input Method(Inputting of telephone numbers included)

1. Telephone Number and NAM Programming Method .............................................................. 14

CHAPTER 3. Circuit Description

1. RF Transmit/Receive Part ....................................................................................................... 17

2. Digital/Voice Processing Part .................................................................................................. 22

CHAPTER 4. Trouble Shooting

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General Introduction

The LG-YD2750 cellular phone functions as digital cellular phone worked in CDMA (Code Division
Multiple Access) mode.

CDMA mode applies the DSSS (Direct Sequence Spread Spectrum) technique that has been used in
military. This technique enables to share one frequency channel with many users in the same specific
area. As a result, that it increases the capacity 10 times more compared with that in the analog mode
(AMPS) currently used.

Soft/Softer Handoff, HaID Handoff, and Dynamic RF power Control technologies are combined into
this phone to reduce the call being interrupted in a middle of talking over phone.

CDMA digital cellular network consists of MSC (Mobile Switching Office), BSC (Base Station
Controller), BTS (Base station Transmission System), and MS (Mobile Station). Communication
between MS and BTS is designed to meet the specification of TIA/EIA/IS-95-A/B/C (Common Air
Interface). MS meets the specifications of the below :

- TIA/EIA/IS-95-A/B/C (Common Air Interface) : Protocol between MS and BTS

- TIA/EIA/IS-96-B : Speech CODEC

- TIA/EIA/IS-98 : Basic MS functions

- IS-126 : Voice loopback

- TIA/EIA/IS-99 : Short Message Service, Asynchronous Data Service, and G3 Fax Service

LG-YD2750 is composed of a transceiver, a adapter, a Li-Polymer Battery.

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CHAPTER 1. System Introduction

1. System Introduction

1.1 CDMA Abstract

The cellular system has a channel hand-off function that is used for collecting the information on the
locations and movements of radio mobile telephones from the cell site by automatically controlling
several cell site through the setup of data transmission routes and thus, enabling one switching
system to carry out the automatic remote adjustment. This is to maintain continuously the call state
through the automatic location confirmation and automatic radio channel conversion when the busy
subscriber moves from the service area of one cell site to that of another by using automatic location
confirmation and automatic radio channel conversion functions. The call state can be maintained
continuously by the information exchange between switching systems when the busy subscriber
moves from one cellular system area to the other cellular system area.

In the cellular system, the cell site is a small-sized low output type and utilizes a frequency allocation
system that considers mutual interference, in an effort to enable the re-use of corresponding
frequency from a cell site separated more than a certain distance. The analog cellular systems are
classified further into an AMPS system, E-AMPS System, NMT system, ETACS system, and JTACS
system depending on technologies used.

Unlike the Time Division Multiple Access (TDMA) or the Frequency Division Multiple Access (FDMA)
used in the band limited environment, the Code Division Multiple Access(CDMA) system which is one
of digital cellular systems is a multi-access technology under the interference limited environment. It
can process more number of subscribers compared to other systems (TDMA system has the
processing capacity three times greater than the existing FDMA system whereas CDMA system,
about 12~15 times of that of the existing system).

CDMA system can be explained as follows: TDMA or SDMA can be used to enable each person to
talk alternately or provide a separate room for each person when two persons desire to talk with each
other at the same time, whereas FDMA can be used to enable one person to talk in soprano, whereas
the other in bass (one of the two talkers can carry out synchronization for hearing in case there is a
bandpass filter function in the area of the hearer).

Another method available is to make two persons to sing in different languages at the same time,
space, and frequency when wishing to let the audience hear the singing without being confused. This
is the characteristics of CDMA.

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LG-YD2750

On the other hand, when employing the CDMA technology, each signal has a different
pseudo-random binary sequence used to spread the spectrum of carrier. A great number of CDMA
signals share the same frequency spectrum. In the perspective of frequency area or time area, several
CDMA signals are overlapped. Among these types of signals, only desired signal energy is selected
and received through the use of pre-determined binary sequence; desired signals can be separated
and then, received with the correlator used for recovering the spectrum into its original state. At this
time, the spectrums of other signals that have different codes are not recovered into its original state
and instead, processed as noise and appears as the self-interference of the system.

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2. Features and Advantages of CDMA Mobile Phone

2.1 Various Types of Diversities

When employing the narrow band modulation (30kHz band) that is the same as the analog FM
modulation system used in the existing cellular system, the multi-paths of radio waves create a
serious fading. However, in the CDMA broadband modulation(1.25MHz band), three types of
diversities (time, frequency, and space) are used to reduce serious fading problems generated from
radio channels in oIDer to obtain high-quality calls.
Time diversity can be obtained through the use of code interleaving and error correction code
whereas frequency diversity can be obtained by spreading signal energy to more wider frequency
band. The fading related to normal frequency can affect the normal 200~300kHz among signal bands
and accoIDingly, serious affect can be avoided. Moreover, space diversity (also called path diversity)
can be realized with the following three types of methods.
First, it can be obtained by the duplication of cell site receive antenna. Second, it can be obtained
through the use of multi-signal processing device that receives a transmit signal having each different
transmission delay time and then, combines them. ThiID, it can be obtained through the multiple cell
site connection (Soft Handoff) that connects the mobile station and more than two cell sites at the
same time.

2.2 Power Control

The CDMA system utilizes the forwaID (from a base station to mobile stations) and backwaID (from
the mobile station to the base station) power control in oIDer to increase the call processing capacity
and obtain high-quality calls. In case the originating signals of mobile stations are received by the cell
site in the minimum call quality level (signal to interference) through the use of transmit power control
on all the mobile stations, the system capacity can be maximized.
If the signal of mobile station is received too strong, the performance of that mobile station is improved.
However, because of this, the interference on other mobile stations using the same channel is
increased and accoIDingly, the call quality of other subscribers is reduced unless the maximum
accommodation capacity is reduced.
In the CDMA system, forwaID power control, backwaID open loop power control, and closed loop
power control methods are used. The forwaID power control is carried out in the cell site to reduce the
transmit power on mobile stations less affected by the multi-path fading and shadow phenomenon and
the interference of other cell sites when the mobile station is not engaged in the call or is relatively
nearer to the corresponding cell site. This is also used to provide additional power to mobile stations
having high call error rates, located in bad reception areas or far away from the cell site.
The backwaID open loop power control is carried out in a corresponding mobile station; the mobile
station measures power received from the cell site and then, reversely increases/decreases transmit
power in oIDer to compensate channel changes caused by the forwaID link path loss and terrain

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characteristics in relation to the mobile station in the cell site. By doing so, all the mobile office
transmit signals in the cells are received by the cell site in the same strength.
Moreover, the backwaID closed loop power control used by the mobile station to control power with
the commands issued out by the cell site. The cell site receives the signal of each corresponding
mobile station and compares this with the pre-set threshold value and then, issues out power
increase/decrease commands to the corresponding mobile station every 1.25 msec (800 times per
second).
By doing so, the gain tolerance and the different radio propagation loss on the forwaID/backwaID link
are complemented.

2.3 Voice Encoder and Variable Data Speed

The bi-directional voice service having variable data speed provides voice communication which
employs voice encoder algorithm having power variable data rate between the mobile telephone cell
site and mobile station. On the other hand, the transmit voice encoder performs voice sampling and
then, creates encoded voice packets to be sent out to the receive voice encoder, whereas the receive
voice encoder demodulates the received voice packets into voice samples.
One of the two voice encoders described in the above is selected for use depending on inputted
automatic conditions and message/data; both of them utilize four-stage frames of 9600, 4800, 2400,
and 1200 bits per second. In addition, this type of variable voice encoder utilizes adaptive threshold
values when selecting required data rate. It is adjusted in accoIDance with the size of background
noise and the data rate is increased to high rate only when the voice of caller is inputted.
Therefore, background noise is suppressed and high-quality voice transmission is possible under the
environment experiencing serious noise. In addition, in case the caller does not talk, data transmission
rate is reduced so that the transmission is carried out in low energy. This will reduce the interference
on other CDMA signals and as a result, improve system performance (capacity, increased by about
two times).

2.4 Protecting Call Confidentiality

CDMA signals have the function of effectively protecting call confidentiality by spreading and
interleaving call information in broad bandwidth. This makes the unauthorized use of crosstalk, search
receiver, and radio very haID substantially. Also included is the encryption function on various
authentication and calls specified in IS-95 for the double protection of call confidentiality.

2.5 Soft Handoff

During the soft hand, the cell site already in the busy state and the cell site to be engaged in the call
later participate in the call conversion. The call conversion is carried out through the original call

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connection cell site, both cell sites, and then, new cell site. This method can minimize call
disconnection and prevent the user from detecting the hand-off.

2.6 Frequency Re-Use and Sector Segmentation

Unlike the existing analog cellular system, the CDMA system can reuse the same frequency at the
adjacent cell and accoIDingly, there is no need to prepare a separate frequency plan. Total
interference generated on mobile station signals received from the cell site is the sum of interference
generated from other mobile stations in the same cell site and interference generated from the mobile
station of adjacent cell site. That is, each mobile station signal generates interference in relation to the
signals of all the other mobile signals.
Total interference from all the adjacent cell sites is the ratio of interference from all the cell sites
versus total interference from other mobile stations in the same cell site (about 65%). In the case of
directional cell site, one cell normally uses a 120°sector antenna in oIDer to divide the sector into
three. In this case, each antenna is used only for 1/3 of mobile stations in the cell site and accoIDingly,
interference is reduced by 1/3 on the average and the capacity that can be supported by the entire
system is increased by three times.

2.7 Soft Capacity

The subscriber capacity of CDMA system is flexible depending on the relation between the number of
users and service classes. For example, the system operator can increase the number of channels
available for use during the busy hour despite the drop in call quality. This type of function requires
40% of normal call channels in the standby mode during the handoff support, in an effort to avoid call
disconnection resulting from the lack of channels.
In addition, in the CDMA system, services and service charges are classified further into different
classes so that more transmit power can be allocated to high class service users for easier call set-up;
they can also be given higher priority of using hand-off function than the general users.

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3. Structure and Functions of CDMA Mobile Phone

The mobile station of CDMA system is made up of a radio frequency part and logic/control (digital)
part. The mobile station antenna is connected with the transmitter/receiver via a SAW duplexer filter
so that it can carry out the transmit/receive function at the same time.

The transmit frequency is the 25MHz band of 824~849MHz, whereas the receive frequency is the
25MHz band of 869~894MHz. The transmit/receive frequency is separated by 45MHz. The RF signal
from the antenna passes the LNA , bandpass SAW filter having the 1.25MHz band and then, is
directly converted into baseband signal by the frequency synthesizer and frequency down converter.
Baseband output signals that have been filtered from spurious signal are converted into digital signals
via an analog-to-digital converters(Rx ADC) and then, sent out respectively to 5 correlators in each
CDMA de-modulator. Of these, one is called a searcher whereas the remaining 4 are called data
receiver(finger). Rx signals include a great number of call signals that have been sent out by the
adjacent cells. These signals are detected with pseudo-noise sequence (PN Sequence). Signal to
interference ratio (C/I) on signals that match the desired PN sequence are increased through this type
of correlation detection process. Then, other signals obtain processing gain by not increasing the ratio.
The carrier wave of pilot channel from the cell site most adjacently located is demodulated in oIDer to
obtain the sequence of encoded data symbols.

During the operation with one cell site, the searcher searches out multi-paths in accoIDance with
terrain and building reflections. On three data receivers, the most powerful four paths are allocated for
the parallel tracing and receiving. Fading resistance can be improved a great deal by obtaining the
diversity combined output for de-modulation. Moreover, the searcher can be used to determine the
most powerful path from the cell sites even during the soft handoff during the two cell sites. Moreover,
four data receivers are allocated in oIDer to carry out the de-modulation of these paths. Data output
that has been demodulated change the data string in the combined data row as in the case of original
signals(deinterleaving), and then, are de-modulated by the forwaID error correction decoder which
uses the Viterbi algorithm.

On the other hand, mobile station user information sent out from the mobile station to the cell site pass
through the digital voice encoder via a mike. Then, they are encoded and forwaID errors are corrected
through the use of convolution encoder. Then, the oIDer of code rows is changed in accoIDance with
a certain regulation in oIDer to remove any errors in the interleaver. Symbols made through the above
process are spread after being loaded onto PN carrier waves. At this time, PN sequence is selected
by each address designated in each call.

Signals that have been code spread as above are digital modulated (OQPSK) and then, power
controlled at the automatic gain control amplifier (AGC Amp). Then, they are converted into RF band
by the frequency synthesizer synchronizing these signals to proper output frequencies. Transmit
signals obtained pass through the duplexer filter and then, are sent out to the cell site via the antenna.

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4. Specification

4.1 General Specification

4.1.1 Transmit/Receive Frequency Interval :

4.1.2 Number of Channels (Channel Bandwidth) :

4.1.3 Operating Voltage :

4.1.4 Battery Power Consumption :

SLEEP IDLE MAX POWER

CDMA

4.1.5 Operating Temperature :

4.1.6 Frequency Stability :

4.1.7 Antenna :

Fixed PIFA Type (Internal), 50

DC 3.2~4.2V

1.2 mA 100 ~ 150 mA 580 mA (25dBm)

-30° ~ +60°

±0.5PPM

DC 3.7V

45MHz

Ω

20CH (BW : 1.23MHz)

4.1.8 Size and Weight

Size : 108.5 x 44.5 x 15.6mm (L x W x D)

•

Weight : TBD

•

4.1.9 Channel Spacing :

4.1.10 Battery Type, Capacity and Orerating Time

Stand-By Time

Talk Time

1.25MHz

StandaID (1000mAh)

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Unit = Hours, Minutes

160 Hrs (SCI=1)

180 Min (About +92dBm, Half rate)

4.2 Receive Specification

4.2.1 Frequency Range :

869.820 MHz ~ 893.190 MHz

4.2.2 Local Oscillating Frequency Range :

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1738.08MHz ~ 1787.94MHz

LG-YD2750

4.2.3 Intermediate Frequency :

4.2.4 Sensitivity :

4.2.5 Selectivity :

4.2.6 Spurious Wave Suppression :

4.2.7 CDMA Input Signal Range

• Dynamic area of more than -115~ -12.6 dB : 102.4dB at the 1.23MHz band

-104dBm ( C/N 12dB or more)

3dB C/N Degration (With Fch ± 1.25KHz : -30dBm)

MSM6XXX seires (Zero IF)

Maximum of -80dB

4.3 Transmit Specification

4.3.1 Frequency Range :

4.3.2 Intermediate Frequency :

4.3.3 Output Power :

824.820 MHz ~ 848.190 MHz

MSM6XXX seires (Zero IF)

0.282W

4.3.4 Interference Rejection

• Single Tone : -30dBm at 900 kHz

• Two Tone : -43dBm at 900 kHz & 1700kHz

4.3.5 CDMA TX Frequency Deviation :

4.3.6 CDMA TX Conducted Spurious Emissions

• 900kHz : - 42 dBc/30kHz below

• 1.98MHz : - 54 dBc/30kHz below

4.3.7 CDMA Minimum TX Power Control :

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±300Hz or less

- 50dBm below

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4.4

MS (Mobile Station) Transmitter Frequency

FA NO. CH.NO. CENTER FREQUENCY FA NO. CH.NO. CENTER FREQUENCY

1
2
3
4
5
6
7
8
9

10

1011

29

70
111
152
193
234
275
316
363

824.640 MHz

825.870 MHz

827.100 MHz

828.330 MHz

829.560 MHz

830.790 MHz

832.020 MHz

833.250 MHz

834.480 MHz

835.890 MHz

11
12
13
14
15
16
17
18
19
20

404
445
486
527
568
609
650
697
738
779

837.120 MHz

838.350 MHz

839.580 MHz

840.810 MHz

842.04 MHz

843.270 MHz

844.500 MHz

845.910 MHz

847.140 MHz

848.370 MHz

4.5

MS (Mobile Station) Receiver Frequency

FA NO. CH.NO. CENTER FREQUENCY FA NO. CH.NO. CENTER FREQUENCY

1

1011

869.640 MHz

11

404

882.120 MHz
2
3
4
5
6
7
8
9

10

29

70
111
152
193
234
275
316
363

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4.6 Charge time

4.6.1 StandaID Battery :

870.870 MHz

872.100 MHz

873.330 MHz

874.560 MHz

875.790 MHz

877.020 MHz

878.250 MHz

879.480 MHz

880.890 MHz

Typical 120 ~ 180 Min.

12
13
14
15
16
17
18
19
20

445
486
527
568
609
650
697
738
779

883.350 MHz

884.580 MHz

885.810 MHz

887.04 MHz

888.270 MHz

889.500 MHz

890.910 MHz

892.140 MHz

893.370 MHz

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5. Installation

5.1 Installing a Battery Pack (Soft Pack type)

1) The soft battery pack is keyed so it can only fit one way. Align the groove in the battery pack with
the rail on the back of the phone until the battery pack rests flush with the back of the phone.

2) Insert the bottom of battery into the openning on the back of the phone. Then, push the battery
cover up until the latch clicks.

5.2 For Adapter Use

1) Plug the adapter into a wall outlet. The adapter can be operated from either a 110V or a 220V
source.

2) Insert the adapter jack into the phone with the installed battery pack.

Red light indicates battery is being charged. Green light indicates battry is fully charged

5.3 For Mobile Mount

5.3.1 Installation Position

In oIDer to reduce echo sound when using the Hands-Free Kit, make sure that the speaker and
microphone are not facing each other and keep microphone a generous distance from the speaker.

5.3.2 Interface Box

Choose an appropriate flat surface ( somewhere under the dash on the passenger side is preferred )
and mount the IB bracket with the four self-tapping screws provided. Clip the IB into the IB bracket.

5.3.3 Microphone Installation

Install the microphone either by cliiping I onto the sunvisor (driver’s side) or by attaching it to door post
(driver’s side), using a velcno adhesive tape (not included).

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5.3.4 Cable Connections

5.3.4.1 Power and Ignition Cables

Connect the red wire to the car battery positive terminal and the black wire to the car ground. Connect
the green wire to the car ignition sensor terminal. ( In oIDer to operate HFK please make sure to
connect green wire to ignition sensor terminal.) Connect the kit’s power cable connector to the
interface box power receptacle.

5.3.4.2 Antenna Cable Connection

Connect the antenna coupler cable connector from the cradle to the external antenna connector. ( Antenna is not
included.)

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CHAPTER 2. NAM Input Method

(Inputting of telephone numbers included)

1. Telephone Number and NAM Programming Method : TBD

• Press [#+#+#+#].

Then, the following Menu is appeared.

DEBUG MENU

Service Mode

1
2 Test Screen
3 Test Call
4 Vocoder Set

5 Hybrid Pref

Sel

• If you press [1] , display the PHONE MODEL.

DEBUG MENU

PHONE

Service Mode

1

MODEL

2 Test Screen
3 Test Call
4 Vocoder Set

5 Hybrid Pref

• You can’t edit PHONE MODEL , then press [OK].

1
2 Test Screen
3 Test Call
4 Vocoder Set

5 Hybrid Pref

95

OK

DEBUG MENU

Service Mode

SLOT CYCLE

INDEX

1

OK

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• You can edit SLOT CYCLE INDEX (, but not recommended ), then press [OK].

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DEBUG MENU

Service Mode

1

NAM 1

PHONE NUMBER

2 Test Screen

0000000000

3 Test Call
4 Vocoder Set

5 Hybrid Pref

OK

Enter the phone number, then press [OK].

•

DEBUG MENU

Service Mode

1

NAM 1
NAME

2 Test Screen

Empty

3 Test Call
4 Vocoder Set
5 Hybrid Pref

Edit OK

Edit the name of NAM1, the press [OK].

•

‘NAM 1 NAME’ may display the name of the service provider

DEBUG MENU

Service Mode

1

NAM 1

Standard Program

2 Test Screen

IS COMPLETE

3 Test Call
4 Vocoder Set

5 Hybrid Pref

Add End

• Now, the basic programming is completed. To reset the handset, press [Done]. If you want to

program detail informtions for NAM 1, press [

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Add

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The detail programming method is same as basic programming. Set up required values and then,
press the [OK] soft key in an effort to move to the next screen.
To return to the last item, press the [
The editable NAM items are followed:

SERVICE SECURITY CODE
NAM 1 MOBILE COUNTRY CODE
NAM 1 MOBILE NETWORK CODE
NAM 1 PRL Enabled ?
NAM 1 CDMA Home System Reg
NAM 1 CDMA Foreign SID Reg
NAM 1 CDMA Foreign NID Reg
NAM 1 CDMA Home SID/NID
NAM 1 Lock out SID/NID
NAM 1 CDMA Primary CH A
NAM 1 CDMA Secondary CH A
NAM 1 CDMA Primary CH B
NAM 1 CDMA Secondary CH B

Back

].

NAM 1 ACCOLC 0

Editing this items is not recommended.

※

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CHAPTER 3. Circuit Description

1. RF Transmit/Receive Part

1.1 Overview

The RF transmit/receive part employs the direct conversion architecture (ZIF, Zero Intermediate
Frequency). The transmit/receive frequency is respectively 824.04~848.97MHz and 869.04~893.97
MHz. The block diagram is shown in [Figure 3-1].
RF signals received through the antenna are fed into RFR6122 through the duplexer. And then, they
pass the low noise amplifier (LNA), combined with the signals of local oscillator (VCO) at the
frequency mixer in oIDer to create baseband signal directly.
Baseband signals created are changed into digital signals by the analog / digital converter (ADC, A/D
Converter) and then, auto gain controlled and, sent to the MSM6000 (Mobile Station Modem) of the
digital circuit part. Then, they are demodulated by the modulator / demodulator.
In the case of transmission, MSM6000 modulates, interpolates, and converts the digital signal into an
analog baseband before sending it to the RFT6122.
RFT6122 receives OQPSK-modulated anlaog baseband signals from the MSM6000’s Tx part. The
RFT6122 upconverts the Tx analog baseband into RF.
The RFT6122 connects directly with MSM6000 using an analog baseband interface. In RFT6122, the
baseband quadrature signals are upconverted to the Cellular Tx frequency bands and amplified to
provide signal drive capability to the power amp.
After that, the RF signal is amplified by the Power Amp in oIDer to have enough power for radiation.
Finally, the RF signal is sent out to the cell site via the antenna after going through the duplexer

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[Figure 3-1] Block Diagram Of YD2750

1.2 Description of Receive Part Circuit

1.2.1 Duplexer (DP100)

The duplexer consists of the receive part bandpass filter (BPF) and the transmit part bandpass filter
(BPF) which have the function of separating transmit/receive signals in the full duplex system using
the transmit/receive common antenna. The transmit part BPF is used to suppress noises and spurious
waves entering the receive band among transmit signals in oIDer to prevent the drop in receive
sensitivity characteristics. The receive part BPF blocks the signals sent out from entering the receive
end in oIDer to improve sensitivity characteristics.
Insertion loss (IL) in the transmit band is 2.8dB (Max), whereas IL in the receive band is 2.1dB (Max).
The receive band attenuation amount of transmit filter is 51dB (Min) and the transmit band attenuation
amount of receive filter is 45dB or more (Min).

1.2.2 LNA (U104)

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The RFR6122 has cellular LNA. The characteristics of Low Noise Amplifier (LNA) are low noise
figure, high gain, high intercept point and high reverse isolation. The frequency selectivity
characteristic of mobile phone is mostly determined by LNA.

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The specifications of YD2750 LNA are described below

Parameter Gain Mode 0(G0) Gain Mode 1(G1) Gain Mode 2(G2) Gain Mode 3(G3) Unit

Gain

Noise Figure

Input IP3

1.2.3 Rx RF SAW FILTER (F101)

The main function of Rx RF SAW filter is to attenuate mobile phone spurious frequency, attenuate
noise amplified by the LNA and suppress second harmonic originating in the LNA.

1.2.4 Down-Converter Mixers (U104)

The RFR6122 device performs signal direct-down-conversion for Cellular applications. It contains all
the circuitry (with the exception of external filters) needed to support conversion of received RF
signals to baseband signals. The LO Buffer Amplifier buffers the RF VCO to the RF Transmit
Upconverter. RFR6122 offers the most advanced and integrated CDMA Rx solution designed to meet
cascaded Noise Figure (NF) and ThiID-oIDer Intercept Point (IIP3) requirements of IS-98C and
J-STD-018 specifications for Sensitivity, Two-Tone Intermodulation, and Single-tone Desense.

10 7 15 15 dBm

16 4 -5 -20 dB

1.5 5 5.5 20 dB

Operation modes and band selection are specially controlled from the Mobile Station Modem MSM6000.
The specification of YD2750 Mixers are described below:

Parameter High Gain Mode Low Gain Mode Unit

Noise Figure

Input IP3
Input IP2

4 0 dBm

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10 25 dB

56 30 dBm

1.3 Description of Transmit Part Circuit

1.3.1 Description on the Internal Circuit of MSM6000 (U201) and RFT6122 (U103)

For the transmit data path(Tx), the MSM6000 modulates, interpolates, and converts the digital signal
into an analog baseband before sending it to the RFT6122. The RFT6122 upconverts the Tx analog
baseband into RF. The MSM6000 communicates with the external RF and analog baseband to control
signal gain in the RF Rx and Tx signal paths, educe base band offset errors, and tune the system
frequency reference.

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LG-YD2750

The RFT6122 baseband-to-RF Transmit Processor performs all Tx signal-processing functions
required between digital baseband and the Power Amplifier Module (PAM). The baseband quadrature
signals are upconverted to the Cellular frequency bands and amplified to provide signal drive
capability to the PAM. The RFT6122 includes an mixer for up-converting analog baseband to RF, a
programmable PLL for generating Tx and Rx LO frequency, cellular driver amplifier and Tx power
control through an 85 dB VGA. As added benefit, the single sideband upconversion eliminates the
need for a band-pass filter normally required between the upconverter and driver amplifier.
I, I/, Q and Q/ signals proceed from the MSM6000 to RFT6122 are analog signal. In CDMA mode,
These signals are modulated by Offset Quadrature Phase Shift King (OQPSK). I and Q are 90 deg.
out of phase, and I and I/ are 180 deg. The mixer in RFT6122 converts baseband signals into RF
signals. After passing through the upconverters, RF signal is inputted into the Power Amplifier Module.
The RFT6122 Cellular CDMA RF specifications are described below:

Condition Min. Typ. Max. Unit

Rated Output Power

Min Output Power

Rx band noise power

ACPR

1.3.2 Power Amplifier (U102)

The power amplifier that can be used in the CDMA mode has linear amplification capability.
For higher efficiency, it is made up of one module (Monolithic Microwave Integrated Circuit) for which
RF input terminal and internal interface circuit are integrated onto one IC after going through the GaAs
HBT (heterojunction bipolar transistor) process.
The module of power amplifier is made up of an output end interface circuit including this module.
The maximum power that can be inputted through the input terminal is +7dBm and conversion gain is
about 28.5dB. RF transmit signals that have been amplified through the power amplifier are sent to
the duplexer.

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Average CDMA Cellular 6 dBm
Average CDMA Cellular -75 dBm

CDMA Cellular -132 dBm/Hz

Cellular: Fc±885kHz

Fc±1.98MHz

-52

-63

dBc

dBc

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LG-YD2750

1.4 Description of Frequency Synthesizer Circuit

1.4.1 Voltage Controlled Temperature Compensation Crystal Oscillator (U407)

The temperature range that can be compensated by VC-TCXO which is the reference frequency
generator of a mobile station is -30~+80 °C.
VC-TCXO receives frequency tuning signals called TRK_LO_ADJ from MSM6000 as 0.5V~2.5V DC
via R and C filters in oIDer to generate the reference frequency of 19.20MHz and input it into the
frequency synthesizer of UHF band. Frequency stability depending on temperature is ±2.0 ppm.

1.4.2 Voltage Controlled Oscillator (U104)

The internal VCO signal of RFR6122 is processed by the LO generation and distribution circuits in
RFR6122 to create Cellular quadrature downconverter’s LO signals. The LO signals applied at the
mixer ports are at the frequency different than the VCO frequency. This assures that the VCO
frequency is different than the RF frequency, an important consideration for Zero-IF processing. The
VCO frequency used are 1738.08~1787.94MHz for cellular and It is produced in single voltage
controlled oscillator of U106.

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LG-YD2750

2. Digital/Voice Processing Part

2.1 Overview

The digital/voice processing part processes the user's commands and processes all the digital and
voice signal processing in oIDer to operate in the phone. The digital/voice processing part is made up
of a keypad/LCD, receptacle part, voice processing part, mobile station modem part, memory part,
and power supply part.

2.2 Configuration

2.2.1 Keypad/LCD and Receptacle Part

This is used to transmit keypad signals to MSM6000. It is made up of a keypad backlight part that
illuminates the keypad, LCD part that displays the operation status on to the screen, and a receptacle
that receives and sends out voice and data with external sources.

2.2.2 Voice Processing Part

The voice processing part is made up of an audio codec in MSM6000 used to convert MIC signals into
digital voice signals and other external MIDI Synthesizer used to convert digital voice signals into
analog voice signals, amplifying parts for amplifying the voice signals and MIC signals are on external
MIDI Synthesizer and Codec in MSM6000.

2.2.3 MSM6000 (Mobile Station Modem) Part

MSM6000 is the core elements of a CDMA mobile station and carries out the functions of CPU,
encoder, interleaver, deinterleaver, Viterbi decoder, Mod/Demod, codec, and vocoder.

2.2.4 Memory Part

The memory part is made up of a flash memory, SRAM for storing data.

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2.2.5 Power Supply Part (U400, PM6610-2)

The power supply part (PM6610) is made up of devices for generating various types of power, used
for the digital/voice processing part and one DC/DC converter directly connetted to Batterry for LCD
display.

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LG-YD2750

2.3 Circuit Description

2.3.1 Keypad/LCD and Receptacle Part

Once the keypad is pressed, the key signals are sent out to MSM6000 for processing. In addition,
when the key is pressed, the keypad lights up through the use of 10 YELLOW LEDs and LCD
backlights up through the use of 2 white LEDs. The status and operation of a mobile station are
displayed on the screen for the user with the characters and icons on the LCD.
Receptacle(CON301) exchanges audio signals and data with external sources and external power.
Battery Connector receives power from the battery.

2.3.2 MSM Part

MSM6000 is the core element of a CDMA mobile station that includes ARM7TDMI microprocessor
core. The subsystems within the MSM6000 include a CDMA processor, a multi-standaID Vocoder, an
integrated CODEC with earpiece and microphone amplifiers, general-purpose ADC for subsytem
monitoring, an ARM7TDMI microprocessor, an RS-232 serial interfaces supporting forwaID and
reverse link data communications of 307.2 Kbps simultaneously. And it also contains complete digital
modulation and demodulation systems for CDMA cellular standaIDs, as specified in IS-95-A/B/C.

The CPU controls total operations of the subscriber unit. Digital voice data, that have been inputted,
are encoded using the QCELP algorithm. Then, they are convolutionally encoded so that error
detection and correction are possible. Coded symbols are interleaved in oIDer to avoid a burst error.
Each data channel is scrambled by the long code PN sequence of the user in oIDer to ensure the
confidentiality of calls.
Moreover, binary quadrature codes are used based on Walsh functions in oIDer to discern each
channel. Data created thus are 4-phase modulated by one pair of Pilot PN code and they are used to
create I and Q data.
When received, I and Q data are demodulated into symbols by the demodulator and then,
de-interleaved in reverse to the case of transmission. Then, the errors of data received from Viterbi
decoder are detected and corrected. They are voice decoded at the vocoder in oIDer to output digital

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voice data.
The MSM6000 also supports Enhanced Variable Rate Coder (EVRC) operation in addition to the
standaID 8k and 13k vocoding rating.

2.3.2.1 Audio Processing Part

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LG-YD2750

MIC signals are inputted into the audio codec, and amplified with programmable gain, and converted
into digital signals(PCM). Then, they are inputted into MSM6000.
In addition, digital audio signals(PCM) outputted from MSM6000 are converted into analog signals
after going through the audio codec. These signals are amplified with programmable gain on codec’s
internal AMP and external MIDI Synthesizer, transferred to the ear-piece.

2.3.3 Memory Part

The memory part consists of a 32Mbits Flash Memory and a 16Mbits SRAM. On the Flash Memory,
there are programs used for the operation of a mobile station and the non-volatile data of the mobile
station such as a ESN(Electronic Serial Number) are stored. The programs can be changed through
down loading after the assembling of mobile stations. On the SRAM, data generated during the
operation of a mobile station are stored temporarily.

2.3.4 Power Supply Part

When the battery voltage (+4.2V) is fed and the PWR key of keypad is pressed, the power-up circuitry
in PM (power management) IC (U401) is activated by the PWR_ON_SW/ signal, and then the LDO
regulators embedded in PMIC for MSM are operated and +1.90V_MSMC, +2.85V_MSMP and
+2.6V_MSMA are generated.
The Rx part regulator (+2.6V_RX) is operated by the SBI(Seiral Bus Interface) control signal from
MSM6000. The Tx part regulator (+2.6V_TX) is operated by SBI(Seiral Bus Interface) control signal
from MSM6000.
The block diagram of power management IC is shown in [Figure 3-2].

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[Figure 3-2] Block Diagram Of Power Management IC

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LG-YD2750

2.3.5 Logic Part

The Logic part consists of internal CPU of MSM6000, SRAM, FLASH ROM.
The MSM6000 receives TCXO (19.20MHz) clock signals from X100, and then controls the phone
during the CDMA mode. The major components are as follows:

CPU : ARM7TDMI microprocessor core

MEMORY :

FLASH ROM : 32Mbits (U202, K8D3216UTC-DI07)

•

STATIC RAM : 16Mbits (U203, K6F1616U6C-XF70)

•

CPU

The ARM7TDMI 32-bit microprocessor is used and CPU controls all the circuitry. Some of the
features of the ARM microprocessor include a 3 stage pipelined RISC architecture, both 32-bit ARM
and 16-bit THUMB instruction sets, a 32-bit address bus, and a 32-bit internal data bus. It has a high

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performance and low power consumption.

FLASH ROM and SRAM

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LG-YD2750

Flash Memory is used to store the program of the mobile station. Using the down-loading program,
the program can be changed even after the mobile station is fully assembled.
SRAM is used to store the internal flag information, call processing data, and timer data.

KEYPAD

For key recognition, key matrix is setup using KEY_SENSE0-4_N signals and GPIO 21,57-61 of
output ports of MSM6000. 10 LEDs and backlight circuitry are included in the keypad for easy
operation in the dark.

LCD MODULE

LCD module contains a controller which will display the information onto the LCD by 16-bit data
from the MSM6000. It is also supplied stable 2.85V_MSMP by inner regulator in U400 for fine view
angle and and LCD reflects to improve the display efficiency. 2 white LEDs are used to display LCD
backlight

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CHAPTER 4. Trouble Shooting

CHAPTER 4. Trouble Shooting

4.1 Rx Part Trouble

4.1.1 When Rx Power isn’t enough

Test Point

VCTCXO

Checking Flow

Rx TEST SETUP(HHP)

- Test Channel : 384

E5515C Setup

- CH : 384

- Sector Power : -30 dBm
Spectrum Analyzer Setting
Oscilloscope Setting

Duplexer

VCTCXO

START

3

4

5

2

PMIC

RFR6122

1

Figure 4-1

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1. Check

PMIC Circuit

2. Check

VCTCXO Circuit

3. Check
Rx VCO

4. Check

Control Signal

5. Check
Duplexer

Mobile SW

6. Check

Rx I/Q data

Redownload SW, CAL

4.1.2 Checking Regulator Circuit

Test Point

U400. 7 High

U400. 31 (+2.6V_RX)

Circuit Diagram

Figure 4-2

Checking Flow

Check Pin 31
of U400

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Check Pin 7
of U400

+2.6V_Rx OK?

PMIC Circuit is OK See

next Page to check

VCTCXO

No

Pin 7. High?

Replace U400

No

Changing Board

4.1.3 Checking VCTCXO Circuit

Test Point

U407. 4

U407. 3

Figure 4-3

Circuit Diagram

U400. 32

Check U407 Pin 3

◆ Refer to Graph 4-1(a)

19.2MHz OK?

CheckU407 Pin 4

◆ Refer to Graph 4-1(b)

+2.8V_TCXO OK?

Check U400

Checking Flow

Yes

No

No

VCTCXO Circuit is Ok
See next Page to check
Rx VCO

Yes

Changing U407

Waveform

Graph 4-1(a)

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Graph 4-1(b)

4.1.4 Checking Rx VCO Signal

Test Point

U104.16 (CP_RX)

Checking Flow

U104.18 (UHF_LO_OUT)

Figure 4-4

Check U104 Pin 18
Check if there is
Any Major Difference

◆ Refer to Graph 4-2
Check U104 Pin 16

Check if the voltage is
around 1.5V

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Rx TEST SETUP(HHP)

- Test Channel : 384(DCN),600(PCS)
Spectrum Analyzer Setting
Oscilloscope Setting

UHF_LO OK?

No

CP_RX OK?

Yes

Replace U104

Yes

No

Rx VCO is Ok

See next Page

to check Control Signal

Check U103

1763.04MHz @ DCN384

DCN Mode

Graph 4-2

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4.1.5 Checking Control Signal

Test Point

U104. 5 (SBST)

Checking Flow

U104. 4 (SBCK)

U104. 3 (SBDT)

Figure 4-5

Waveform

Check Pin 3, 4, 5

◆ Refer to Graph 4-3(a,b)
Check SBDT, SBCK SBST

Check if there is
Any Major Difference

◆ Refer to Graph 4-3(a,b)

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SBDT

SBCK

Level is High?

Yes

Similar?

Yes

Control Signal is Ok

See next Page to check

Duplexer

No

No

Download the SW

Download the SW

SBST

SBCK

Graph 4-3(a) Graph 4-3(b)

4.1.6 Checking Mobile SW & SP3T & Duplexer(DCN,PCS)

Test Point

U100. 2

DP101. 2

DP101. 7

Circuit Diagram

Figure 4-6

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Checking Flow

Rx TEST SETUP(HHP)

- Test Channel : 384(DCN),600(PCS)

E5515C Setup

- CH : 384(DCN),600(PCS)

- Sector Power : -30 dBm
Spectrum Analyzer Setting
Oscilloscope Setting

Waveform

Check U100 Pin 2

Check if there is
Any Major Difference

◆ Refer to Graph 4-4(a)

Check DP101 Pin2

Check if there is
Any Major Difference

◆ Refer to Graph 4-4(b)

Check DP101 Pin 7

Check if there is
Any Major Difference

◆ Refer to Graph 4-4(c)

Detected Signal?

No

Detected Signal?

No

Detected Signal?

No

DCN Duplexer is Ok

See next Page to check

Rx I/Q data Signal

Yes

Yes

Yes

Changing U100

Check C100

Changing DP101

U100 Pin 2

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Graph 4-4(a)

Waveform

DP101 Pin2

Graph 4-4(c)

DP101 Pin 7

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Graph 4-3(c)

4.1.7 Checking Rx I/Q data

Test Point

Waveform

U104. 28 (Rx_I_P)

U104. 27 (Rx_I_M)

U104. 26 (Rx_Q_M)

U104. 25 (Rx_Q_P)

Figure 4-7

U104. 28 (Rx_I_P)

Graph 4-5(a)

Checking Flow

Check U104 Pin 25, 26, 27, 28
Check if there is
Any Major Difference

◆ Refer to Graph 4-5(a,b)

U104. 27 (Rx_I_M)

U104. 25 (Rx_Q_P)

U104. 26 (Rx_Q_M)

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Graph 4-5(b)

Similar?

Yes

Redownload the

Software Calibrate

No

Replace U104

4.2 Tx Trouble

Test Point

Mobile S/W

Duplexer VCTCXO

PAM

RFT6122

Checking Flow

√ Connect the phone to UART connector
√ Press H/W or F7, then click ‘offline-d’

-Click ‘Band select‘ to cdma & Tx on &Power Amp

-Set channel to 384 & AGC :400

√ Spectrum analyzer setting
√ Oscilloscope setting

On

START

4. Check

RFT6122 Circuit

1. Check

Regulator(PMIC) Circuit

6. Check

PAM Circuit

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7. Check

2. Check

VCTCXO Circuit

Duplexer & Mobile SW

Circuit

√ RedownloadSW, CAL

3. Check

SBI Control Signal

4.2.1 Check Regulator(PMIC) Circuit

TEST POINT

U400 Pin 16

(+2.8V_MSMP)

U400 Pin 29

(+2.6V_Tx)

Circuit Diagram

U400 Pin 13

(+2.85V_TX_REG)

U400 Pin 4

(+4.2V_Vbatt)

Checking Flow

Check Pin 4, 13, 16, 29

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U400

+2.6V_TX

+2.8V_MSMP

+2.85V_TX_REG

+4.2 Vbatt

OK?

YES

Regulator Circuit is OK

See Next Page to Check

VCTCXO

U201

NO NO

U201 Pin E14

TX ON High?

YES

Replace U400

Replace U201

4.2.2 Check VCTCXO Circuit

TEST POINT

U407 Pin4 (

+2.8V_TCXO)

U407 Pin3

(TCXO)

Circuit Diagram

Checking Flow

X100

Pin 3

19.2MHz OK?

NO

Pin4

2.8V OK?
NO

Check U400

YES

YES

VCTCXO Circuit is OK

See next page to check

SBI control signal

Replace U407

Waveform

U407 Pin3 TCXO

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U407 Pin4 +2.8V_TCXO

4.2.3 Check SBI Control Signal

Test Point

Circuit Flow

U103 Pin 1, 2, 32

(SBST,SBDT,SBCK)

Check Pin 1,2,32

Waveform

Level is appear?

YES

Similar Waveform?

YES

Control Signal is OK

See next page to check

RFT6122 Circuit

NO

NO

Download the SW

Download the SW

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SBDT

SBCK

SBST

SBCK

4.2.4 Check RFT6100 Circuit

Test Point

U103 Pin23
(CELL_OUT)

C158,C159

(TX_I, Q)

Circuit Flow

Check C158,C159

I,Q Level is Appear?

YES

NO

U103 Pin12

(TX_CP)

Check U201

Check U103 Pin12

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Check U103 Pin23

Level (near 1V) is Appear?

YES

Output signal

CELL is Appear?

YES

Control Signal is OK

See next page to check

PAM Circuit

NO

NO

Replace U103

Replace U103

Circuit Diagram

Waveform

SPECTRUM ANALYZER CONDITION

-RBW : 1MHz,VBW: 1KHz

-Span : 60MHz

-Frequency : DCN( 836.52MHz)

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C158,C159 TX_I,Q DATA

U103 Pin23 DCN_OUT

4.2.5 Check PAM Circuit

Test Point

U102 Pin3

(Vmode 0.7~2.1V)

U102 Pin4

(Vref +2.85V)

U102 Pin2

(RF_IN)

U102 Pin 1,8

(Vcc1,2)

U102 Pin7

(RF_OUT)

Circuit Diagram

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4.2.6 Check Duplexer & Mobile SW

TEST POINT

DP100 PIN2

DP_out

U100 PIN1

Mobile S/W out

Circuit Flow

Check DP100 Pin2

DUP_OUT

Check U100 Pin1

Level is Appear?

YES

Level is Appear?

YES

Redownload SW and

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Recalibration

NO

NO

Replace DP100

Replace U100

Circuit Flow

Check U102 Pin2

RF_IN

Check U102 Pin4

V_REG

Check U102 Pin3

DCN:Vcont (0.7v~2.1v)

Check U102 Pin1, 8

VCC1,2

Check U102 Pin7

RF_OUT

Input Level is Appear?

YES

Vref 2.7~2.85V

OK?

YES

Level is

OK?

YES

Level is

3.4V~4.2V OK?
YES

Output Level

is Appear?

YES

PAM Circuit is OK

See next page to check

Duplexer & Mobile SW

NO

NO

NO

NO

NO

Check F100

Check Q100, U400

Check U201

Replace U101

Replace U102

Waveform

SPECTRUM ANALYZER CONDITION

-RBW : 1MHz,VBW: 1KHz

-Span : 60MHz

-Frequency : DCN( 836.52MHz)

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U102 Pin2 DCN PAM_IN U102 Pin7 DCN PAM_OUT

Circuit Diagram

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4.3 Logic Part Trouble

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Figure 4.3.1 PMIC(PM6610) FUNCTIONAL BLOCK DIAGRAM

4.3.1 Power On Trouble

Circuit Diagram

Test Points

29 (+2.6V_TX)

31 (+2.6V_RX)

Figure 4.3.2 Power Management circuit diagram

16 (+2.8V_MSMP)

14 (+2.4V_MSMC)

11 (+2.6V_MSMA)

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U400
PMIC

U201(MSM)

8 (PWR_ON_SW)

7 (PS_HOLD)

32(+2.8V_TCXO)

Figure 4.3.3 PM6610 POWER MANAGEMENT SECTION

Checking Flow

START

YES

Check Battery Voltage

> 3.2V ?

YES

Push power-on key and check

the level change of

U400 PWR_ON_SW high?

YES

Check the voltage of

the following port at U400

+2.4V_MSMC
+2.8V_MSMP
+2.6V_MSMA

+2.8V_TCXO

+2.6V_RX
+2.6V_TX

YES

NO

NO

Charge of Change Battery and try again

Check the contact of power-key

or dome switch

NO

Replace U400

NO

NO

Re-download software & try again

Does it work properly?

YES

NO

Replace the main board.

Logic level at PS_HOLD

of U201=High ?

YES

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Does it work properly?

YES

The Phone will power on.

The power-on procedure is completed.

The problem may be elsewhere.

4.3.2 Charging Trouble

U400

Test Points

Circuit Diagram

Q401

Q401

Figure 4.3.4 CHARGER CIRCUIT PART

R461

Block Diagram

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Figure 4.3.5 PM6610 CHARGING CONTROL BLOCK

Checking Flow

SETTING : Connect the battery and the charging adaptor (TA) to the phone

START

YES

Charging Connector

CON300

Well-soldered?

YES

Voltage at

Pin1(V_CHAR)

of CON300 = 5V?

YES

Q401,R461

well-soldered?

YES

Does U400 and Q401

work Properly?

YES

Is the battery

charged

NO

NO

NO

NO

NO

Re-soldering CON300

The charging adaptor (TA) is out of order.
Change the charging adaptor.

Re-Soldering Q401,R461

Change the U400 or Q401

The battery may have the problem

Change the battery and try again.

YES

Charging will operate properly

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4.3.3 Audio AMP Trouble

Test Points

Pin6

(AUDIO_GAI

N_SEL)

CON403

Circuit Diagram

L404

L403

Figure 4.3.6 RECEIVER PART

R428
R422

Pin6

(+VBATT)

U409 U408

U401

R423

Pin4

(SPK_-IN)

Block Diagram

Figure 4.3.7 RECEIVER PART

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Figure 4.3.8 RECEIVER CODEC BLOCK

Checking Flow

SETTING : “Ringers” at Sounds menu

START

Voltage at Pin6 of

U401 is over

3.4~4.2V?

Yes

Does Speaker work Properly?

Yes

The R423(SPK_EN) is High?

Yes

The Pin6 of U402 is
High : Speaker mode
Low : Receiver mode

Check the signal

level at L403, 404

NO

NO

NO

NO

Change main board.

Internal pattern is opened

Check the contact of speaker or

Replace the speaker

Check the

soldering R423

Replace the MSM or Board

Check the soldering

L403, L404

Yes

NO

Re-soldering R423

NO

Re-soldering L403, L404

Yes

Yes

Check the signal

level of EAR10+ at

R422, R428

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Check the signal

level at Pin4 of

Does U401 work

Speaker will work properly

Yes

U401

Yes

properly?

Yes

NO

NO

NO

Replace the MSM

Re-soldering or

Replace the U402

Re-soldering or

Replace the U401

4.3.6 MIC Trouble

Test points

R434

Figure 4.3.9 MIC & BIAS PART

Circuit Diagram

C440

U403

Mic filter

C439

Figure 4.3.10 MIC FILTER PART

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Figure 4 .3.11 MIC & MIC FILTER

Checking Flow

SETTING : After initialize 5515C, Test US Cellular

START

Voltage at R434 = 1.2V?

(MIC BIAS Voltage Check)

Yes

Check the signal level

At each side of MIC. Is

It a few tens mVAC?

Yes

Check the soldering of

C439, C440

Yes

Check the soldering of

MIC Filter Part

Yes

MIC will work properly

No

No

No

No

Check the soldering

Of R434

Yes

Replace MSM

Replace the microphone

Re-solder C439, C440

Re-solder MIC Filter part

No

Re-solder R434

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4.3.7 Vibrator Troble

Checking Flow

R416 R417

Q406

LED414

Q403 R436

Figure 4.3.12 Vibrator PART

Circuit Diagram

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Figure 4.3.13 VIBRATION CONTROL BLOCK

Checking Flow

SETTING : “Vibrator on” at Sounds of test menu

START

Check the state of

Contact of Vibrator

Yes

Does Vibrator work Properly?

Yes

Is the voltage across LED414

over 2.5V?

Yes

Is the voltage across R436

Under 3V?

No

No

No

No

Re-contact vibrator

Replace Vibrator

Check the soldering of

Q406, R417, LED400

Replace Q406, R417, LED414

Check the soldering of

Q403, R436

Yes

No

Re-soldering Q406, R417, LED414

No

Re-soldering Q403, R436

Yes

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Check the signal level at

MSM_MOTOR_EN=high?

Yes

Vibrator will

Work properly

No

Yes

Replace Q403, R436

Replace MSM

4.3.8 Key Backlight LED Trouble

Test Points

R415 Q400

Figure 4.3.14 KEYPAD B ACK LIGHT PART

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Figure 4.3.15 KEYPAD Back Light Circuit

Checking Flow

Is the voltage level VBATT

START

No

Charge or Change Battery and try again

3.2-4.2V?

Yes

No

No

No

Check the soldering of each R or

replace LEDs not working

Check the condition of Q400, R415.

If problem, Change Q400, R415.

Replace MSM

Are all LEDs LED404~417

working?

Yes

Q400, R410 is working?

Yes

Check the signal level at

KEY_BACK_EN=high?

Yes

BACKLIGHT WILL

WORK PROPERLY

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4.3.9 Earphone Trouble

Test Points

C430

R206

U203

U404
C212

MSM

CON401

Circuit Diagram

R207

Figure 4.3.16 EAR MIC JACK PART

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Figure 4.3.17 EAR MIC JACK PART

Checking Flow

START

Insert the earphone to the handset.

Yes

Does the audio

Profile of the phone change to

the earphone mode?

Yes

Set the audio part of the test

equipment to echo mode

Yes

Can you hear your voice

from the earphone?

Yes

Audio path problem

SETTING : After initialize 5515C, Test US Cellular

Earphone detect problem

No

Change the earphone and

Can you hear your voice

from the earphone?

try again.

Yes

Yes

No

No

Set the audio part of the

test equipment to

continuous wave mode

Can you hear the sound

from the earphone?

Yes

Yes

1

Earphone sending

path problem

Earphone receiving

Path problem

No

2

4

Earphone will
work properly

Change Earphone.

3

Earphone receiving path problem

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Check soldering of

2

Level of C430

is about 1.2V

Yes

Pin 3 of CON401

Yes

Change

main board

No

No

Download

S/W

Re-soldering of

Pin 3 of CON401

Earphone detect problem

1

Level of pin 5 of CON401

about 1.6V?

5

Check soldering

Check working

Yes

U404

Yes

U404

Yes

4

Earphone detect

problem

No

No

No

Level of R206, R207

about 2.4V?

No

Re-soldering R206, R207

Re-solder U404

Replace U404

Yes

5

Earphone sending path problem

Earphone

sending

3

Level pin4 of CON401

is about 1.6V

path problem

No

Re-solder

R206, R207

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Yes

Level of C232 is

About a few tens

or hundreds VAC?

Yes

No

Re-solder

C232

Does it work well?

Yes

4

Yes

No

Re-download

software

Does it work well?

Change main

No

board

4.3.10 LCD Trouble

Test Points

CON303

R400:403

Q405

C315

U202

LED400:403

Q300

L300

VR300,VR301

Circuit Diagram

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Figure 4.3.18 LCD CONNECTOR PART

C326

Figure 4.3.19 LCD CONNECTOR

Checking Flow : LCD

START

Check L300, C315 Voltage

(MSMP)= 2.8V ?

Yes

Check the

CON303 Soldering

Yes

Does LCD work properly?

Check voltages at each

point of Capacitor.

Yes

No

Re-Soldering L300,C315

No

Re-Soldering CON303

No

Change the LCD Module

Check the

Control signal

D[0:7], LCD_RESET/,

LCD_RS/, LCD_CS/,

LWR/,RD/

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Yes

LCD display will

work properly

No

Does VR300,VR301, R326

Work Properly?

Yes

Change the Main Board

No

Re-soldering or Replace

VR300,VR301, R326

Checking Flow : Back Light

START

Check the LED400:403

R400:403

Yes

Does Q405 work Properly?

Yes

Check the signal level at

LCD_BACK_EN=high?

Yes

LCD backlight will

work properly

No

No

No

Re-soldering or Replace

LED400:403, R400:403

Re-Soldering or

Replace Q405

Replace MSM

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4.3.11 When UIM isn’t operating

Test Point

Q407 No.1

CON402 No.1

Circuit Diagram

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Checking Flow

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