Ericsson KRD 103 117/1, Руководство по обслуживанию, Страница: 6 / 54

REGULATORS
Transistor Q507 and the power module (pin 6 of IC501) are
directly connected to the battery through a fuse F1. When the
power switch of the radio is turned off, the current drain is al-
most zero.
When the power switch of the radio is turned ON, IC605
supplies 5.6V to most of the sections and IC502 supplies 5.6V
to the VCO and synthesizer section.
In the receive mode, pin 11 of the microprocessor releases a
logical low level and turns transistor Q5 on. Q5 supplies 5.6V
to the receiver section.
In the transmit mode, pin 51 of the microprocessor releases
a logical low level and turns transistor Q505 on. Q505 supplies
5.6V to the transmitter section.
Components F1, D3, D4 and C50 reduce the damage to
other parts in the radio should a short circuit occur within the
radio or the polarity of the DC voltage is reversed.
LOGIC SECTION
The logic section contains the following:
•
Microprocessor
•
EEPROM memory
•
Rx Tone Decoder
•
2-Tone Decoder
•
Tx Tone Encoder
•
Tone Generator
•
Memory Back-up
•
Reset Circuit
Microprocessor (IC601)
The microprocessor controls many of the transmit and re-
ceive functions. The microprocessor operates according to the
software instructions stored in the internal Read Only Memory
(ROM).
EEPROM (IC604)
The Electrically Erasable Programmable Read Only Mem-
ory (EEPROM) can be reprogrammed through the external mi-
crophone and speaker jacks J2 and J3.
IC604 stores the customer parameters such as channel in-
formation and function parameter. Since this device is a non-
volatile memory, IC604 retains all information in the
EEPROM even when power is removed.
The programming adapter is connected to the external mi-
crophone and speaker jacks J2 and J3. When the external
speaker output J3 is set to a logical high for a few seconds
from the programming adapter, that signal passes to pin 55 of
IC601 through R37 and D2. The radio enters into external pro-
gramming mode. During programming, several commands and
data are exchanged through J2 between pins 19 and 20 of the
microprocessor.
The microprocessor sends serial data to the EEPROM
IC604 to store custormer data such as clock (pin 14), data (pin
13) and ROM enable (pin 50).
Receive Tone Decoder (IC705, IC602 And Q601)
This circuit contains switched capacitor low pass filter
IC602 that is used in both transmit and receive modes. IC603
switches IC602 to function as either receive tone filter or trans-
mit tone filter. The two op-amps in IC602 are comparators to
convert the analog waveform to digital waveform.
In the receive mode, the Tx/Rx control (pin 51 of IC601)
supplies a logical high signal to pins 5 and 6 of IC603. The
analog switches (pins 3 and 4, 8 and 9) in IC603 turn on. The
receive tone from the IF IC (pin 15 of IC1) is supplied to the
band pass filter IC705 through the gate of IC603 (pins 3 and
4).
When the radio receives DCSS data, the microprocessor
(pin 18 of IC601) sends a logical high to pin 13 of IC603. The
gate of IC603 (pins 1 and 2) turns on. The received DCSS code
is sent to the low pass filter (pin 8 of IC602).
Clock pulses from the microprocessor (pin 12) are applied
to pin 10 of IC705 and pin 9 of IC602, providing the cut-off
frequency of the filter as f
c
= f
clk
x 50.
The output signal of IC705 enters the low pass filter (pin 8
of IC602). The low pass filter only passes the desired tone and
filters out high frequencies contained in the receive data signal.
Filtered data is applied to pin 3 of IC602 and supplied to
op-amp #1 (pin 13 of IC602) through the gate of IC603 (pins 8
and 9). In this op-amp, receive data is amplified to approxi-
mately 1.2 Vp-p of level at pin 14 of IC602 (adjusted by
RT601). The amplified data is supplied to a comparator (pin 14
of IC602, op-amp #2).
When the voltage at pin 14 of IC602 becomes greater than
that at pin 1, a logical low is released at pin 2 of IC602. When
the voltage at pin 14 of IC602 decreases lower than pin 1, a
logical high is released at pin 2 of IC602. Voltage at pin 1 of
IC602 provides a reference level of the comparator around
the center of the data waveform.
Digitized data (square wave) is released at pin 2 of IC602
and applied to the microprocessor (pin 16) for decoding.
2-Tone Decoder
The received signal is also sent to the 2-tone decoder (pin
13 of IC704). The microprocessor provides serial data to
IC704 such as clock, data and enable signals to set tone in-
formation. The result of IC704 is sent to pin 38 of IC601.
Transmit CTCSS Tone Or DCSS Encoder
(IC602)
In the transmit mode, the microprocessor sets the Tx/Rx
control (pin 52) to a logical low to turn Q505 on. The Tx 5V
is sent to pin 12 of IC603. The analog switch (pins 10 and
11) in IC603 turns on. The transmit tone or DCSS square
wave signal from the microprocessor (pin 17 of IC1) is sup-
plied to the low pass filter (pin 8 of IC602) through the gate
of IC603 (pins 10 and 11).
Clock pulses from the microprocessor (pin 12) are ap-
plied to pin 9 of IC602, providing cut-off frequency of the
low pass filter the same as the decoder.
Filtered CTCSS tones or DCSS signals (pin 3 of IC602)
are applied to the sum-amplifier (pin 6 of IC702) through
RT701 (adjusts transmit deviation of the tone).
Tone Generator (IC601)
The microprocessor generates beep tone at pin 10 and
alerts the user of certain conditions in the radio. The gener-
ated tone is supplied to the volume controller (pin 4 of IC3)
to monitor from the speaker and and transmit sum-amplifier
(pin 6 of IC702) to modulate.
Memory Back-Up
Regulator IC605 supplies voltage to pins 72 aand 73 of
the microprocessor through D601. It also charges C618
through R616.
The microprocessor retains in Random Access Memory
(RAM) selected channel, deleted channels and scan status
while the power switch is turned off.
When the microprocessor senses that power is turned off
(pin 21 of IC601 goes low), the current drain into the micro-
processor is decreased to save battery power, while the
power is turned off (standby mode).
When the power switch is off, the stored charged in
C618 keeps the microprocessor "alive" during the standby
mode.
Reset Circuitry
IC606 contains a Schmitt-Trigger circuit that maintains
the output voltage at approximately 0.7 V until the input
voltage reaches approximately 4.25V. When the input volt-
age exceeds 4.15V, IC606 releases an output voltage of the
same level after a delay of approximately 200 microseconds.
When the output voltage of IC606 is high, a positive ris-
ing pulse is supplied to Q602 through C613. Q602 then re-
leases a short duration, low pulse that is sent to pin 25 of
IC601. The microprocessor resets and normal operation be-
gins.
Figure 2 - Test Setup, Transmitter
AE/LZB 119 1658 R1A
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