Filter
Top Products
Mafntenance
-
494A1494Ap
Servtce
Vot.
1
a. lf
the
calculated
and
measured
frequencies
are
within
50 MHz
of
each
other
and
the
mbasured
fre_
quency
agrees
with
the
internally
count€d
1st
LO
Freg
readout
or
differs from
it
by a
multiple
of
the
Auxiliary
Synthesizer
Freq,
r€turn
to
normal
opera_
tion-
(by pressing
<Btue-SHtFT>).
Now
attempt
to
calibrate
the
CF
Control
board
and
the
1st
LO Driver
board
by
pressing
<Btue-SHIFT>
PULSE
STRETCHER
and
select
#1
from
the
menu
for
the
FREQUENCY
LOOPS
CAL, and
#1
again
for
the
CF
Control board.
or
#2
for
the lst
LO
Driver
board.
Exit
from
the
CF Control
board calibration
routine
by
pressing
<Blue-SHtFT>
when
the step
for
Ra040
ii
displayed.
lf
you
are
able
to complete
the calibra-
tion
routin€,
check
to
gee
if
the error
message
is
still
present.
lf it
is,
or if
the
calibration
routines
cannot
be
completed,
continue
troubleshooting
with
step
4.
(E)
b.
lf
the calculat€d
and
measured
frequencies
are
within
50 MHz,
but
do
not
m€Et
the above
condition
in
step
3a, measure
the Auxiliary
Synthesizer
output
frequency
at
P1060
on
the
Auxiliary
Synthesizer
board.
0)
lf
the Auxitiary
Synthesizer
output
frequency
is
coffect,
measure
the input
frequency
lrom
the
Harmonic
Mixer
with a spectrum
analyier,
at
the
cabte
connection
to
p261
on
ttre
euiitiary
Syn_
thesizer
board.
(A
counter
woutd probaOiy
give
an
eroneous
reading
because
of
the
harmonic
mixing
process).
The
frequency
measured
with
the speetrum
analyzer
should
equal
the sum of
the Desired
Mixer
Freq
and
the
measured
1st
LO
frequency,
less
the Desired
lst
LO
Freq, if
the catculated
frequency
is
between
10
MHz
and
90 MHz.
lf
the calculat€d
frequency
is
outside
th€ 10
MHz
to
g0
MHz range,
the
lst
Lo
fre_
quency
is far
from
the d€sired
value.
Repeat
the
previous
steps
in
this
procedure.
(a)
lf
the Harmonic
Mixer
output
frequency
is
correct.
measure
the frequency
at
edge con_
nector
'l5,
on
the
Auxillary
synthesizer
board,
with
a countgr.
This
should
be
1i100th
of
the Harmonic
Mixer
output
fre_
quency.
(b)
A
correct
frequency
measurement
indi_
cates
the
Counter
board
is
defective.
(E)
(c)
An
incorrect
frequency
measurement
indicates
the
Auxiliary
Synthesizer
is
defec-
tive.
(E)
(d)
The
Harmonic
Mixer
is
probably
defec_
tive
if
no
signal
is
present
at
the output
or
the signal
frequency
is
incorrect.
{E)
(2)
tf
the
output
frequency,
at
p1060
is
incorrect,
measure
fie
200_220
MHz
VCo
tune
voltage
between
Tp1066
and
Tp1074
on the
Auxiliary
Synthesizer
board.
The
range
of the
tuning
voltage
is
normally
+S
V
to +12
V.
6-10
(a)
lf
the
tune
voltage is
within
th€
center
of
its
normal
range and
the output
frequency
at
P1060
is stable
(varies
no
more
than l-
2Hzl,
the
programmable
divider
in
the
phase-locked
loop
is
probably
defective.
(E)
(b)
lf
the
tune
voltage is
in
th€
center
portion
of its
normal
range
and
the output
frequency
at P1061
is
unstable, the
loop amplifier
ii
probably
defective.
(E)
(c)
lf
the
tune
voltage
and
oscillator
fre-
guency
are
at
the
end or
outside
their
range,
in
the same
dir€ction
(high
or low),
C1070 tn
the VCO
may
be
misadjusted.
lf
adjustment
of
the capacitor
do'es not
conect
the
prob-
lem it is
not in
the
VCO
but somewhere else
in
the loop.
(E)
(d)
lf
th€
tuning
voltage
and
the Auxitiary
Synthesizer frequency
are in opposite
direc-
tions
from
the
c€nter
of
their respective
ranges
(8.5V
and 210
MHz),
the VCO is
prob-
ably
defective.
(E)
{e)
lf the calculated and
measured
frequen-
cies
difier
by more than
50 MHz, remove
the
jumper
plug
P3043
on
the 1st
LO
Driver
board
and
measure the oscillator current.
The oscillator
coil has significant
inductance.
Interrupting the oscilla-
tor
current
will
gen€rate
hlgh vol-
tage.
Remove/replace
P3043
or
connect/disconnect a
current
meter
after
the
power
is off.
fiypical
vol-
tages at
P3043
can range
as high as
35
V.)
The coil
current should
be: 40 mA/y,
where
the voltag€ is
the
sense-resistor
voltage
as
previously
measured
across
Rl040. The
measured current should
be within 1olo of
this
value.
(3)
lf
the
measured
and
calculated
currents
are
within 17o. return
to
normal op€ration
(by
press-
ing
<Blue-SHIFT>)
and
determine if the
fre-
quency
control
error
occurs
with frequency
span/div of
5 MHz or less, or above
5
MHz/div,
with the sam€ center
fr€qu€ncy.
The frequency
range should
be in either band 1 or
band
2.
(a)
lf
the
frequency control
error occurs
only
with
frequency
spans
of
5
MHz/div or
less,
one of
the noise
filter capacitors
on the
1st
LO Assembly
is
probably
defective.
(E)
O
o
o
o
o
I
o
I
o
o
o
o
o
o
o
o
o
o
o
a
a
o
C
o
o
o
o
o
o
o
I
a
t
o
I
o
o
o
o
o
o
o
o
a