G700-U10 Smartphone
Maintenance Manual
10 Circuit and Failure Analysis
Issue 1.0 (2013-07-22)
Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
55
Circuit Analysis
The LCD BTB connector J1301 connects the LCD module to U401. The LCD module uses
high-speed MIPI data lines (one group for clock signals and four groups for data signals) for
signal transmission and supports a refresh rate of 60 Hz. T1301 to T1305 are the
common-mode chokes for five groups of the MIPI data lines and used to prevent the
interference from entering the LCD module and radiating to other components. With the
frame synchronization function, the LCD uses LPTE as the data transmission synchronization
signal to avoid screen tearing. The LCD module has three power supplies, VDD18_PMU,
VSP, and VSN. VSP and VSN are provided by U1302. The LCD_ID1 and LCD_ID2 signals
are used to identify the LCD manufacturer. Signal
00
indicates CMI, and signal
11
indicates
AUO. The initialization signal LRSTB is effective when at low level. The backlight control
signal LCD_CABC is used to enable the backlight driving chip U1301 when there is data
transmitted to the LCD.
The location number U1301 indicates the backlight control chip TPS61161. VBAT passes
through the boost circuit and converts into the backlight power supply signals VLED_A,
VLED_K1, and VLED_K2. The 5-inch LCD backlight uses ten LEDs divided into two
groups. LEDs in each group are connected in serial, and the groups are connected in parallel.
A ground resistor of 10 ohms impedance is added to the TPS61161's pin FB to realize the
maximum current of 20 mA (Duty: 100%) for the LEDs. The LED brightness (current output
by the driver) is controlled by the PWM signals output by LCD_CABC. When no data is
transmitted to the LCD, LCD_CABC outputs nothing, and the LCD backlight is turned off.
Troubleshooting Process
Figure 10-28
Troubleshooting LCD failures
LCD failure
Is the power supply
(VDD28_PMU and
VDD18_PMU) to the
LCD normal?
Check U202
Y
Are the signals output to the
LCD normal? Are T1301 to
T1303 disconnected or short-
circuited?
Resolder or replace U401
N
N
Y
Replace J1301
Is the LCD backlight (VLED_P
and VLED_N) normal? Are the
surrounding components
disconnected or short-circuited?
Resolder or replace U1301
Y
N
