Table of Contents
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TROUBLESHOOTING
1.
INTRODUCTION
Servicing
the
SABER
Series
radio requires the
localization
of
the malfunctioning circuit before the
defective component can
be isolated and replaced.
Since
localizing and isolating a defective component
constitutes
the most time
consuming
part of trou-
bleshooting, a thorough understanding
of the
circuits
involved
will aid
the technician
in
performing efficient
servicing. Technicians
must know how one function
affects another; they
must be familiar with the overall
operation
of
the radio and the procedures
necessary
to
place
it
back
in
operation
in
the shortest
possible
time.
The
radio
service
manual, schematic diagrams,
and troubleshooting
procedures provide valuable
information for troubleshooting
purposes.
The service
manual provides signal flow information
in
a
simplified
format, while the
schematic diagrams
provide the
detailed circuitry and the biasing voltages required
for
isolating malfunctioning components. By using the
diagrams, troubleshooting procedures,
and deductive
reasoning processes,
the
suspected circuit
may be
readily found.
To determine
if
analysis
of
the radio is required,
perform
checks
such
as
12dB
SINAD
and rated audio
performance
for the
receiver, and current drain, fre-
quency
error,
and deviation for the transmitter.
These
should
give
the technician
a general
indication
of
the
problem's location.
After the general problem area
of
the radio
has
been identified, careful use
of
a dc
voltmeter,
rf
milli-
voltmeter, and an
oscilloscope should isolate
the prob-
lem to
an individual component.
2.
PRELIMINARY
CHECKS
When a
radio performs unsatisfactorily, the follow-
ing
procedures should help localize the
fault.
a.
Check
Battery
The
first
step
in
localizing a
trouble is
to
ensure
that the battery is fully
charged; ideally, verify
the
operation
of the radio on
a battery
eliminator.
Follow
the troubleshooting procedures
in
this manual, and
the appropriate
service
manual.
b.
Alignment
Strict adherence
to
the published procedures is a
prerequisite
to
accurate alignment
and proper
evalua-
tion of the
performance
of the radio.
The
selection
of
test equipment
is critical.
The
use
of
equipment other
than that recommended should be
cleared through
your Motorola
Area Representative
to
ensure
that
it
is
of
equivalent
quality.
The service
technician must observe good servic-
ing
techniques.
The
use
of
interconnecting
cables
that
are too long, poorly positioned
(dressed),
or
improper-
ly
terminated
will result
in
erratic meter readings,
making
it
impossible
to
tune the radio to the
desired
specifications.
Use
the recommended test equipment
setup and
proper
connections
for
alignment and adjustments.
Refer
to
the detailed procedures supplied
in
the appli-
cable service manual.
c.
Check
Overall Transmitter Operation
If
the battery
voltage
is
sufficient,
check
the overall
performance
of
the transmitter.
A
good overall
check
of
the transmitter is the
rf
power output measurement.
This check indicates
the proper operation of the trans-
mitter
amplifier
stages. A
properly tuned and operating
transmitter will produce the rated
rf
output into
a
50-
ohm load with
a dc
input of
7.5 volts.
If
the
rf
power
measured
is
less
than rated
rf
output, refer
to
the
applicable transmitter troubleshooting procedure.
d.
Check
Overall Receiver Operation
(1) 12CB
SINAD
This
procedure
is
a standard
method for
evaluat-
ing
the performance
of an
FM receiver,
since
it
pro-
vides
a
check
of
the
rf,
i-f,
and audio
stages. The
method
consists
of finding the
lowest modulated
sig-
nal
necessary
to
produce 50%
of
the radio's rated
audio output with a 12dB
or
better ratio of
signal
+
noise + distortion
/
noise + distortion.
This
is termed
"usable sensitivity."
To perform this measurement,
connect the leads
from
a
SINAD
meter
to
the audio output
of
the
test
box.
Set
the Motorola
service
monitor or
rf
signal gen-
erator to output
a
1-millivolt
signal. Modulate the
rf
sig-
nal with
a 1kHz tone
at
3kHz
deviation. Introduce the
signal
to the radio at the
exact channel frequency
through the universal connector.
Set
the volume
con-
trol
for rated
audio output
(3.74Vrms). Decrease
the
rf
signal level
until
the
SINAD
meter reads 12dB.
The
signal generator
output
(12dB
SINAD
measurement)
should be
less
than
0.35yV
on
mid-band and vhf
receivers
or
less
than
0.35uV
on uhf
receivers.
If
the
radio
does
not
meet this specification, refer
to
the
receiver troubleshooting procedure.
3.
VOLTAGE MEASUREMENT
AND SIGNAL
TRACING
To aid
in
troubleshooting,
ac
and dc
voltage read-
ings are provided
(in red) on
the main circuit board,
and
2k
and
8k display circuit boards schematic dia-
grams
in
the
service
manual. When making
these
volt-
age checks, pay
particular attention
to
any notes
that
may
accompany
the
voltage reading
of
a particular
stage.
CAUTION
When checking a transistor
or
module, either
in
or out of the circuit,
do
not
use an
ochmmeter
hav-
ing more than 1.5 volts de appearing
across
the
test leads
or an
ohms
scale
of
less
than x 100.
21
TROUBLESHOOTING
1.
INTRODUCTION
Servicing
the
SABER
Series
radio requires the
localization
of
the malfunctioning circuit before the
defective component can
be isolated and replaced.
Since
localizing and isolating a defective component
constitutes
the most time
consuming
part of trou-
bleshooting, a thorough understanding
of the
circuits
involved
will aid
the technician
in
performing efficient
servicing. Technicians
must know how one function
affects another; they
must be familiar with the overall
operation
of
the radio and the procedures
necessary
to
place
it
back
in
operation
in
the shortest
possible
time.
The
radio
service
manual, schematic diagrams,
and troubleshooting
procedures provide valuable
information for troubleshooting
purposes.
The service
manual provides signal flow information
in
a
simplified
format, while the
schematic diagrams
provide the
detailed circuitry and the biasing voltages required
for
isolating malfunctioning components. By using the
diagrams, troubleshooting procedures,
and deductive
reasoning processes,
the
suspected circuit
may be
readily found.
To determine
if
analysis
of
the radio is required,
perform
checks
such
as
12dB
SINAD
and rated audio
performance
for the
receiver, and current drain, fre-
quency
error,
and deviation for the transmitter.
These
should
give
the technician
a general
indication
of
the
problem's location.
After the general problem area
of
the radio
has
been identified, careful use
of
a dc
voltmeter,
rf
milli-
voltmeter, and an
oscilloscope should isolate
the prob-
lem to
an individual component.
2.
PRELIMINARY
CHECKS
When a
radio performs unsatisfactorily, the follow-
ing
procedures should help localize the
fault.
a.
Check
Battery
The
first
step
in
localizing a
trouble is
to
ensure
that the battery is fully
charged; ideally, verify
the
operation
of the radio on
a battery
eliminator.
Follow
the troubleshooting procedures
in
this manual, and
the appropriate
service
manual.
b.
Alignment
Strict adherence
to
the published procedures is a
prerequisite
to
accurate alignment
and proper
evalua-
tion of the
performance
of the radio.
The
selection
of
test equipment
is critical.
The
use
of
equipment other
than that recommended should be
cleared through
your Motorola
Area Representative
to
ensure
that
it
is
of
equivalent
quality.
The service
technician must observe good servic-
ing
techniques.
The
use
of
interconnecting
cables
that
are too long, poorly positioned
(dressed),
or
improper-
ly
terminated
will result
in
erratic meter readings,
making
it
impossible
to
tune the radio to the
desired
specifications.
Use
the recommended test equipment
setup and
proper
connections
for
alignment and adjustments.
Refer
to
the detailed procedures supplied
in
the appli-
cable service manual.
c.
Check
Overall Transmitter Operation
If
the battery
voltage
is
sufficient,
check
the overall
performance
of
the transmitter.
A
good overall
check
of
the transmitter is the
rf
power output measurement.
This check indicates
the proper operation of the trans-
mitter
amplifier
stages. A
properly tuned and operating
transmitter will produce the rated
rf
output into
a
50-
ohm load with
a dc
input of
7.5 volts.
If
the
rf
power
measured
is
less
than rated
rf
output, refer
to
the
applicable transmitter troubleshooting procedure.
d.
Check
Overall Receiver Operation
(1) 12CB
SINAD
This
procedure
is
a standard
method for
evaluat-
ing
the performance
of an
FM receiver,
since
it
pro-
vides
a
check
of
the
rf,
i-f,
and audio
stages. The
method
consists
of finding the
lowest modulated
sig-
nal
necessary
to
produce 50%
of
the radio's rated
audio output with a 12dB
or
better ratio of
signal
+
noise + distortion
/
noise + distortion.
This
is termed
"usable sensitivity."
To perform this measurement,
connect the leads
from
a
SINAD
meter
to
the audio output
of
the
test
box.
Set
the Motorola
service
monitor or
rf
signal gen-
erator to output
a
1-millivolt
signal. Modulate the
rf
sig-
nal with
a 1kHz tone
at
3kHz
deviation. Introduce the
signal
to the radio at the
exact channel frequency
through the universal connector.
Set
the volume
con-
trol
for rated
audio output
(3.74Vrms). Decrease
the
rf
signal level
until
the
SINAD
meter reads 12dB.
The
signal generator
output
(12dB
SINAD
measurement)
should be
less
than
0.35yV
on
mid-band and vhf
receivers
or
less
than
0.35uV
on uhf
receivers.
If
the
radio
does
not
meet this specification, refer
to
the
receiver troubleshooting procedure.
3.
VOLTAGE MEASUREMENT
AND SIGNAL
TRACING
To aid
in
troubleshooting,
ac
and dc
voltage read-
ings are provided
(in red) on
the main circuit board,
and
2k
and
8k display circuit boards schematic dia-
grams
in
the
service
manual. When making
these
volt-
age checks, pay
particular attention
to
any notes
that
may
accompany
the
voltage reading
of
a particular
stage.
CAUTION
When checking a transistor
or
module, either
in
or out of the circuit,
do
not
use an
ochmmeter
hav-
ing more than 1.5 volts de appearing
across
the
test leads
or an
ohms
scale
of
less
than x 100.
21
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