U8655
Maintenance Manual
9 Principles and Failure Analysis
Issue 1.0 (2012-02-23)
Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
44
Troubleshooting Key Failure
Key failure
Are the FPC and ZIF
c onnec tor c onnec ted
properly ?
Re-connect them
Return the phone
to the factory
Y
N
Is the keypad on the
FPC in good contact
with the dome sheet?
Clean the
keypad and the
dome sheet
N
Y
9.4.6 Status Indicator and Touch Key Backlight Circuits
The U8666's status indicator (tricolor indicator) provides red, green and blue light sources that
are driven by the PM8029's three LED drivers.
Light
Source
Driver Pin (PM8029)
Description
Red
LED_RED_DRV_N (MPP3)
Adjusted using electric current
Green
LED_GREEN_DRV_N (MPP5)
Adjusted using electric current
Blue
LED_BLUE_DRV_N (MPP8)
Adjusted using electric current
The KYPD_DRV_N (PM8029) is used to adjust the brightness of the keypad's backlight, and
VPH_PWR is used to supply power to the backlight LEDs. The keypad backlight is provided
by two white LEDs. The light from the LEDs are transmitted to the key area using a light
guide film.