Motorola Commercial Series Сервісна інформація - Сторінка 6
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1-2
When the radio is turned on, SWB+ is present and is applied to:
transistor switch Q494 (pins 1 and 6) which turns on Q493
RX audio power amplifier U490
voltage divider R420/R421 and port PE0, a microprocessor A/D input which measures battery
voltage and radio on/off status
The output of FET switch Q493 is applied to the control pins of regulators U310, U320 and U330,
turning them on. The following regulators are used:
Reference No.
The 5V source is applied to:
RX back end circuitry
synthesizer super filter input and charge pump supply
RED/GRN LEDs
RX audio buffer U510
portions of ASFIC U451
The 5V source is also applied to FET switches Q311 and Q312. Q311 is turned on by Q313 when
RX_ENA (from U401 pin 49) is high, and supplies the "5R" source to the RF front end stages Q21-
Q22, and the VCO RX injection buffer Q280. Q312 is turned on by Q313 when TX_ENA (from U401
pin 50) is high, and supplies the "5T" source to the first transmitter stage Q100.
The digital 3.3 volt source from U320 (D_3.3V) is applied to:
microprocessor U401
EEPROM U402
S-RAM U403 (not used)
flash ROM U404
The 3V regulated source from U330 is applied to:
synthesizer IC U201
VCO/buffer IC U251
portions of ASFIC U451
microphone bias circuitry
While the radio is turned on, port PH3 (U401 pin 44) is held high. When the radio is turned off,
SWB+ is removed and port PE0 (U401 pin 67) goes low, initiating a power-down routine. Port PH3
(pin 44) remains high, keeping the voltage regulators on via Q493 and Q494, until the operating
state of the radio has been stored in EEPROM and other turn-off data functions have been
completed. PH3 then goes low, turning off Q494 and Q493, and all regulated voltages are removed.
Table 1-1 Voltage Regulators
Description
U310
5V Regulator
U320
Digital 3.3V Regulator
U330
3V Regulator
THEORY OF OPERATION
Type
TK71750S
LP2986
TK71730S