Hytera MD78X, Service Manual

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UHF2 (450
–
520 MHz)
Circuit Description
13
Key Conventional Mode Trunking Mode
S12
Navigation Key S5 and S11
OK/Menu Key S4
Back/Group Call Management Key S6
Power On/Off Key S1
Dial-back/End/Home Screen Key / S2
Redial/Answer/Call Key / S8
LCD
The front panel adopts TFT LCD to transfer data to U302 via the EMIFS data bus. The control signals
include read/write enable signal, memory chip select signal, LCD chip select signal and reset signal,
each of which is pulled up by R36, R35, R34, R33 and R6 respectively. The LCD module is powered by
U5 which converts 5 V into 3.3 V.
LED Indicator and Backlight
The LED enable signal is fed to the serial-to-parallel converter IC (U1), and then is output by U302. RX
status is indicated by green LED, and TX status by red LED. Backlight is activated upon any key press.
The red and green LEDs in series are powered by U902 (5 V) and controlled by Q2 and Q3. The
backlight is also powered by U902 (5 V) and controlled by Q1. Control signals are output via U1.
MMC
For details, please refer to
Interface Definition.
Audio Output
The front panel provides two audio outputs: Handset_audio and Internal_audio (SPK±). Handset_audio
is the external output of received audio via MMC interface, while Internal_audio (SPK±) is connected to
the internal speaker.
Volume Control
The volume control is facilitated by the rotary encoder switch (U7), which generates signals to be fed to
U302 through GPIO17 and GPIO18 for volume adjustment.