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Chapter
1
Description
MSF
5000
Instruction Manual
SSCB
Functional Description
Protection
Circuits
Station protection features provided
by
the
DC-DC
converter include
over-voltage and under-voltage protection. Protection against insufficient
A++
voltage is also provided
by
the
DC-DC
converter to prevent over-discharge of
batteries
during battery
revert.
The
Reset
switch
located on the front panel of
the
Control Tray
generates the
RESET_SWITCH logic
signal. This signal allows the
DC-DC
converter to run regardless of the input voltage, and at the same time
resets the station.
An
insufficient
A++
or under-voltage condition does not shut
down
the station,
but holds
it
in
reset mode.
However,
an over-voltage condition forces the
DC-DC
converter to shut down.
If
this occurs, the converter shuts down and allows the +5
Vdc
reference to discharge to
approximately +2
Vdc
before attempting to restart.
For
a
hard fault (i.e.,
Cca
hardware failure that doesn't correct itself),
the
DC-DC
converter
supply continuously
turns off and attempts to restart
while holding
the
station
in
a reset
mode. Over-current protection for the
Power Supply is also
provided.
Audio Processing
The audio processing circuitry of
the
SSCB
consists
of:
0
Receive
Audio
Processing
Transmit
Audio
Processing
Tone Generating:
Audio Routing
Receive Audio Processing
The input
to the receive
audio processing circuitry is
FM
audio, demodulated
from the
RF
signal by
the receiver
in
the
RF
Tray. Refer to
Figure
1-5
for
a
block
diagram of
the receive
audio processing circuitry.
The receive audio input (RAW
RX1
AUDIO) is
fed to an audio buffer
which
processes the
signal and provides
a
buffered output signal
(QUAD
1
AUDIO). The
QUAD
1
AUDIO
is supplied to the loop-back switch. The loop-back switch usually
passes the
QUAD
1
AUDIO through TP3
as
QUAD AUDIO.
QUAD
1
AUDIO is
also routed to the optional expansion boards.
When
an optional
second receiver is used,
RAW
RX2
AUDIO is
routed to an audio buffer
which
supplies QUAD
2
AUDIO
to the expansion boards
for processing.
QUAD AUDIO
is supplied to the
TTRC
board and to the Secure board.
QUAD
AUDIO is
routed to the audio gate circuit accessed at TP3.
1-12
68P81092E02-
3/19/94
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