Service Manual

MM-E 2072-09333-00
2-41
is made via an RS-485 transceiver, comprising the line receiver U504 and the line driver U505 (refer
to Figure A-3.E).
2-6.2.2 Auxiliary Power Supply
Refer to Figure A-3.E.
The auxiliary power supply is similar to that of the dash-mount version (para. 2-6.1.2).
2-6.2.3 LCD Heater and Backlighting Control
The LCD heater and backlighting control circuits are similar to the dash-mount version (para. 2-6.1.3).
2-6.2.4 Keypad Lighting
The keypad lighting control circuits are similar to the dash-mount version (para. 2-6.1.4).
2-6.2.5 MIC Connector Interface
Refer to Figure A-3.F.
a. The MIC_IN signal is amplified and converted to a balanced signal (TX_AUDIO_P,
TX_AUDIO_N) by the amplifiers in U503, for transmission over the interconnection cable.
b. The PTT_MIC signal is converted to a RS-485 balanced signal by the RS-485 line driver U506.
2-6.2.6 Power Supply Subsystem
Refer to Figure A-3.D.
The power for the CONTROL HEAD module is provided via the 13V8DC line:
a. The linear regulator U501 converts the 13V8DC line to +5V on the 5V0_INT line.
b. The linear regulator U502 converts the 13V8DC line to +8V on the 8V0_AUDIO line. U503
derives a +4V voltage, AUDIO_BIOS, for the MIC IN audio amplifier.
c. The +5V supply voltage is converted by the linear regulator U4 to +3.3V on the 3V3 line.
d. The linear regulator U3 provides +3V to the VDD_LCD_3V0 line.