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Replacing a transistor
or module before
a thorough
check
is made is not recommended.
Read
the volt-
ages
around the
suspected stage.
If
these voltages
are
not
close
to
those specified, the associated com-
ponents should be checked.
A low-impedance
meter should
not
be used for
measurement.
If
all
dc voltages are correct, the signal
should be traced through the circuit
to
show any pos-
sibility of breaks
in
the
signal
path.
4.
TROUBLESHOOTING PROCEDURES
The
troubleshooting procedures
on
the following
pages
will help
isolate troubles
in
the different
sections
of
the radio. Start at the first step
of
the appropriate
procedure and make the
checks as
indicated. Most
usual malfunctions
will
respond
to
the
systematic
approach
to
troubleshooting.
a.
Initial
Checks
(1) Power-up the radio, then
check standby
current:
current should be either 65mA (programmed)
or
40mA (unprogrammed).
If
unprogrammed, com-
plete step (8) and
check
current again.
(2)
Check
the regulators: No.
1
regulator =
5Vdc
(Q1
collector);
No. 2
regulator
=
5Vdc (U103,
pin
8);
receive regulator =
5Vdc (U201,
pin
12).
(3)
Check
that the
RESET
line
(J1,
pin
5) =
5Vdc.
(4)
Check
that the IBP
crystal
(Y400)
frequency
=
7.37 MHz; measure
at
U400,
pin 10.
(5)
Check
for
data activity
(J4,
pin 15)
when the radio
is
powered-up.
(6)
Check
for 2.1
MHz
at pin 17 of
synthesizer
mod-
ule
(U300).
(7)
Check
that the
R/T
line
(U201,
pin
9) =
5Vdc
in
receive
mode; OVdc
in
transmit mode.
(8)
Always
ensure that a known good checksum (test
file) is loaded
into
the radio.
If
the radio has
cus-
tomer data,
save
that particular file and load the
test
file.
b.
Radio Will
Not
Program
(1)
Check
that the
iBP crystal (Y400) frequency
=
7.37 MHz.
(a)
Check
the de
levels
on both
sides
of the
crys-
tal; these
levels are derived
from
microcom-
puter U400.
The levels
should be approxi-
mately
2.0Vdc
and
2.5Vdc.
(b)
1.
If
the
correct dc levels are present and
there is
no
7.37MHz signal, piggyback
another crystal and
check
for
the correct
frequency.
22
(5)
2.
If
the correct dc
levels
are
not
present,
make sure
that all
dc voltages
to
U400 are
correct.
(c)
Check
the continuity
of
L400
with an ohmmeter.
NOTE
Transistor Q403
is only used
to
shift the
crystal
frequency; this does
not
affect the operation of
the crystal.
(2)
Check
the
WATCHDOG TIMER DISABLE
output
line
of
the microcomputer
(U400,
pin
37)
for
a
5Vdc
level. Use an oscilloscope
for
this
check
and
be sure that the line is
not
toggling.
NOTE
Pin
37
of
U400 should always indicate
5Vdc;
this indicates proper operation of the micro-
computer.
If
there is
a checksum (software)
or
hardware error
in
the microcomputer, this line
will
either toggle
or
remain
low.
CAUTION
The
integrated circuits and modules
in
the radio
are static sensitive
devices. DO NOT
attempt to
troubleshoot
or
disassemble
the radio without
first referring
to
the
"Safe
Handling of
CMOS
section of this manual.
Devices" paragraph
in
the
MAINTENANCE
(a)
If
the
voltage reading
is incorrect, attempt
to
reprogram the radio:
1.
If
the radio
will not
program, go
to
step
b
(8).
2.
If
the radio will still not program,
check
that
pin 19 of
U400
is at
a constant
5Vdc
level and
is not
toggling.
(b)
Place a
jumper
across R405;
this
disables
the
RESET
line
to
the microcomputer.
Check
U400,
pin
37 again.
1.
If
the line
does
not
read
5Vdc, suspect
U400.
2.
If
the line
does read 5Vdc, attempt
to
reprogram the radio.
If
the radio will still not
program,
check
pin
30
of U101 for
4Vdc.
If
pin
30
=
4Vdc,
then
suspect U101.
(3)
Check
the volume control
(R800)
voltage range:
(a)
Check
the
voltage range
at
J2,
pin 6, with
an
oscilloscope by
rotating the volume knob from
minimum
to
maximum volume.
The
indication
should be a linear level
increase
from 0 to
5Vdc.
(b)
Repeat step
b
(3) (a)
at pin
56
of
U400.
If
the
volume potentiometer does
not
show a
linear
increase, check the continuity
of
the
PTT/con-
trol
flex circuit.
(4)
Check
the
frequency switch
(S823)
positions:
(a) Take measurements at
J2,
pins
5, 8, 9 and 10.
Rotate the switch through
all
channel posi-
tions and verify
(with
oscilloscope)
that
each
line
has a OVdc and a
5Vdc
level.
(b)
Repeat step
b
(4) (a)
at pins
53, 55, 59, and
61
of
U400.
If
there are
no
indications
on
either step (a) or (b),
check
for the
presence
of
5Vdc
on
the common
line of the
frequency switch.
Verify
with an
oscilloscope
that the
BUSY
line
(J4,
pin
12) is at
a constant 5Vdc level.
NOTE
The
BUSY
line of
U400 reads
low only
when the
DATA
lines (pins 22, 27) are active.
This
is
the
case
when the radio is
first
powered
up.
Replacing a transistor
or module before
a thorough
check
is made is not recommended.
Read
the volt-
ages
around the
suspected stage.
If
these voltages
are
not
close
to
those specified, the associated com-
ponents should be checked.
A low-impedance
meter should
not
be used for
measurement.
If
all
dc voltages are correct, the signal
should be traced through the circuit
to
show any pos-
sibility of breaks
in
the
signal
path.
4.
TROUBLESHOOTING PROCEDURES
The
troubleshooting procedures
on
the following
pages
will help
isolate troubles
in
the different
sections
of
the radio. Start at the first step
of
the appropriate
procedure and make the
checks as
indicated. Most
usual malfunctions
will
respond
to
the
systematic
approach
to
troubleshooting.
a.
Initial
Checks
(1) Power-up the radio, then
check standby
current:
current should be either 65mA (programmed)
or
40mA (unprogrammed).
If
unprogrammed, com-
plete step (8) and
check
current again.
(2)
Check
the regulators: No.
1
regulator =
5Vdc
(Q1
collector);
No. 2
regulator
=
5Vdc (U103,
pin
8);
receive regulator =
5Vdc (U201,
pin
12).
(3)
Check
that the
RESET
line
(J1,
pin
5) =
5Vdc.
(4)
Check
that the IBP
crystal
(Y400)
frequency
=
7.37 MHz; measure
at
U400,
pin 10.
(5)
Check
for
data activity
(J4,
pin 15)
when the radio
is
powered-up.
(6)
Check
for 2.1
MHz
at pin 17 of
synthesizer
mod-
ule
(U300).
(7)
Check
that the
R/T
line
(U201,
pin
9) =
5Vdc
in
receive
mode; OVdc
in
transmit mode.
(8)
Always
ensure that a known good checksum (test
file) is loaded
into
the radio.
If
the radio has
cus-
tomer data,
save
that particular file and load the
test
file.
b.
Radio Will
Not
Program
(1)
Check
that the
iBP crystal (Y400) frequency
=
7.37 MHz.
(a)
Check
the de
levels
on both
sides
of the
crys-
tal; these
levels are derived
from
microcom-
puter U400.
The levels
should be approxi-
mately
2.0Vdc
and
2.5Vdc.
(b)
1.
If
the
correct dc levels are present and
there is
no
7.37MHz signal, piggyback
another crystal and
check
for
the correct
frequency.
22
(5)
2.
If
the correct dc
levels
are
not
present,
make sure
that all
dc voltages
to
U400 are
correct.
(c)
Check
the continuity
of
L400
with an ohmmeter.
NOTE
Transistor Q403
is only used
to
shift the
crystal
frequency; this does
not
affect the operation of
the crystal.
(2)
Check
the
WATCHDOG TIMER DISABLE
output
line
of
the microcomputer
(U400,
pin
37)
for
a
5Vdc
level. Use an oscilloscope
for
this
check
and
be sure that the line is
not
toggling.
NOTE
Pin
37
of
U400 should always indicate
5Vdc;
this indicates proper operation of the micro-
computer.
If
there is
a checksum (software)
or
hardware error
in
the microcomputer, this line
will
either toggle
or
remain
low.
CAUTION
The
integrated circuits and modules
in
the radio
are static sensitive
devices. DO NOT
attempt to
troubleshoot
or
disassemble
the radio without
first referring
to
the
"Safe
Handling of
CMOS
section of this manual.
Devices" paragraph
in
the
MAINTENANCE
(a)
If
the
voltage reading
is incorrect, attempt
to
reprogram the radio:
1.
If
the radio
will not
program, go
to
step
b
(8).
2.
If
the radio will still not program,
check
that
pin 19 of
U400
is at
a constant
5Vdc
level and
is not
toggling.
(b)
Place a
jumper
across R405;
this
disables
the
RESET
line
to
the microcomputer.
Check
U400,
pin
37 again.
1.
If
the line
does
not
read
5Vdc, suspect
U400.
2.
If
the line
does read 5Vdc, attempt
to
reprogram the radio.
If
the radio will still not
program,
check
pin
30
of U101 for
4Vdc.
If
pin
30
=
4Vdc,
then
suspect U101.
(3)
Check
the volume control
(R800)
voltage range:
(a)
Check
the
voltage range
at
J2,
pin 6, with
an
oscilloscope by
rotating the volume knob from
minimum
to
maximum volume.
The
indication
should be a linear level
increase
from 0 to
5Vdc.
(b)
Repeat step
b
(3) (a)
at pin
56
of
U400.
If
the
volume potentiometer does
not
show a
linear
increase, check the continuity
of
the
PTT/con-
trol
flex circuit.
(4)
Check
the
frequency switch
(S823)
positions:
(a) Take measurements at
J2,
pins
5, 8, 9 and 10.
Rotate the switch through
all
channel posi-
tions and verify
(with
oscilloscope)
that
each
line
has a OVdc and a
5Vdc
level.
(b)
Repeat step
b
(4) (a)
at pins
53, 55, 59, and
61
of
U400.
If
there are
no
indications
on
either step (a) or (b),
check
for the
presence
of
5Vdc
on
the common
line of the
frequency switch.
Verify
with an
oscilloscope
that the
BUSY
line
(J4,
pin
12) is at
a constant 5Vdc level.
NOTE
The
BUSY
line of
U400 reads
low only
when the
DATA
lines (pins 22, 27) are active.
This
is
the
case
when the radio is
first
powered
up.
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