Service manual

August 30, 2002 99R85452E01-O
This Page Intentionally Left Blank
8-4
UHF Band Information
: Theory of Operation
8.3 Theory of Operation
8.3.1 General Information
Your radio has two printed circuit boards: the Controller board, and the Radio Frequency (RF) board.
The Controller board contains the CPU/Control section. The RF board contains the VCO/Synthesizer
section, Transmitter section, Receiver section, Transmitter Audio circuitry, Receiver Audio circuitry,
and Battery section.
8.3.2 Power Distribution
Figure 8-1.
The above figure illustrates the DC distribution throughout the radio board. A battery supplies power
directly to the electronic on/off control. Radio power supply is triggered by the Power Switch (On/
Off/Volume control) and +SW B is distributed as show in the figure. Regulator output 5V is supplied
to the CPU. +SW B continues to support the Audio Power AMP, 5V Regulator, TX Regulator until the
radio is turned off.
The radio can be turned off on two ways:
1. Power Switch turned-off
2. Low Battery
When a low battery level is detected by the CPU, it stores the radio personality data to EEPROM
before turning off the radio.
8.3.3 Power up Sequence
1. Power supply is turned on by the On/Off/Volume Control (Power Switch).
2. Power from battery is supplied to the regulator through the switch.
3. Output (5V) from the regulator is directed to the CPU (Q101).
4. Q105 resets the CPU (Q101).
5. The CPU loads radio personality data from EEPROM after the reset.
5V REG
Q204
RX SW
Q211
TX/RX SW
Q208,209
TX REG
Q201,202
RF AMP
Q404
Local AMP
Q416
IF AMP
Q408
IF AMP
Q506
LPF
Q505
HPF
Q502
Audio Power
AMP
Q702
RF PA
Q411
Driver AMP
Q412
MIC AMP
Q602
Sub Audio
LPF Q610
VCO Buffer
Q308
PLL IC
Q323
RF Power
Control
Q419
TX Driver
Q413,414
+ SW B
SAVE SW
Q210
RX +5V
TX +5V
Battery
Diode
Q126
Reset
Q105
CPU
Q101
EEPROM
Q114
DTMF
Decode
Q120
DA
Converter
Q121
Divide
by 2
Q122
Power
Switch
SW201
Ripple Filter
Q318
TX/RX SW
Q317,916
TX VCO
Q303,
Q922
RX VCO
Q302,
Q311