Filter
Top Products
AdJustnent
Procedure
-
494A/4g4Ap
Servtce
Vot. I
To: Vsrt
liignel
Out
(back
penell
Spectnrm
Analyrer
Under Tegt
Flgure
5-25.
Test
equlpm€nt
retup for
adjusting
llre
phase
Lock
assembly.
o
a
o
o
o
o
o
,
a
a
o
I
a
I
o
a
t
I
o
o
o
I
a
a
o
a
o
o
o
o
o
a
t
O
o
o
o
o
o
o
o
o
o
O
(3)
Connect
the
counter
to
the coll€ctor
of
e1040
and
not6 the
frequency.
Frequency
should
equal
the
difference
between pins
N and
K
(e.g.,
25.080
MHz
-
25.000
MHz
-
80
kHz).
Disconnect
the
counter
probe
from
the collector
of
e1040.
(4)
Connect a
test oscilloscope
probe
to the collec-
tor
of
Q1040 and
check
for
a signal
with
a frequency
of
approximately
B0 kHz,
507"
duty cycle,
and
an
amplitude
of
approximatety
5 V
peak-to-peak.
d.
Check Synthesizer
(1)
Set the
SPAN/D|V
to 200
kHz.
phase
tock
should
occur.
{2)
Change
SPAN/DIV
to 500
kHz
and
connect
the
counter
to
J500
on
the
Synthesizer
board.
Check
for
a
reading
of
50.00 MHz.
(3)
Connect
the
counter
to Tp2O40 (Figure
5_26a)
and
check
for
a
reading
that
is near
25.0
MHz.
(4)
Connect
the
test
oscilloscope
to
Tpl040
(Figure
5-26a) and
check
for
positive
pulses
with
an ampli-
tude of approximately
4
V
peak-to-peak.
(5)
Change
the
SPAN/DIV
to
200
kHz and
observe
that
the signal
on
Tpl040,
in
part
d(4) is
stiil
th€re.
G.
Contolled
Osc{llator
-
This
part
of
the
check
is
only
requirgd
after
repair or replac€ment
of
the Con-
trolled Oscillator board.
Bandpass
filter adjustments
c1041 and
C1042 are set
at
the
factory
because they
require
a special
test
fixture. These adjust-
ments
do not
need further adjustm€nt.
lf
adjustment of
C1013
and
C2011
is not
sufncient
to
achieve
phase-lock,
the board
should
be
replaced.
(1)
Press
<Blue-SHIFT> PULSE
STRETCHER
and
select
item #1
(FREQUENCY
LOOPS
CAL), then
item
#5
(PHASE
LOCK
SYNTHESIZER)
from
the
displayed menu.
(2)
Follow
the
instructions
until
the
message,
'VER-
IFY
LAST
STEP'.
Due
to
the interaction
of adjust-
ment
capacitors
C1 013 and
C201
1,
the
two steps
will
have
to
be
repeated
until the
voltages are
correct.
Alternately
press
AUTO RESOLN
and
IDENT
and adjust
until the two
voltage
readings are
correct.
5-26