Service Manual
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and R6 respectively. The 5V voltage is converted to 3.3V by U5, in order to supply the LCD module.
4) LEDs and Backlight
The LED enable signal is fed to the serial-to-parallel converter IC, and then is output by U302. RX status
is indicated by green LED, and TX status by red LED. Backlight is activated upon key press.
The LEDs (red and green) in series are supplied by a 5V voltage (U902) and controlled by Q2 and Q3.
The backlight is also supplied by a 5V voltage and controlled by Q1. Control signals are output via U1.
5) MMC
For details, please refer to Interface Definition.
6) Audio output
The front panel provides two audio outputs: Handset_audio and SPK±. Handset_audio is the output of
received audio via MMC, and SPK± is the output by the audio PA (U201) as audio signal for the front
panel speaker.
7） Volume Control
The volume control is facilitated by the encoder switch (U7), which generates signals to be fed to U302
by GPIO17 and GPIO18.
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