Eddystone 990R - Re-alignment of the AM IF Channel

Re-alignment
of
the AM
IF
Channel
.
Test
Equipment
Standard
Signal
Generator
covering
10.7
MHz
with
provision
for
amplitude
modulation
(30?°}
400
Hz) and
an
output impedance
of
500.
Power
Output
Meter
matched
to
50
impedance.
Miniature
insulated
screwdriver
type trimming
tool.
Connect
generator
output
lead
to base
of
TR15 via the
IF
attenuator
(R57-R59)*
The
connection
should
be
made
in
parallel
with the coaxial
lead to
tags 1 and
2,
the
live
generator
lead
being
blocked
with
a
capacitor of
the order O.OOluF
(tag
1
is
earth).
Connect
the
output
meter
to
the
30
terminals
at
the
rear
of the set
and ensure that
the
external
loudspeaker
is
disconnected.
Use
the
internal
speaker for aural
monitor-
ing
whilst
carrying
out
alignment.
Set
the
receiver
controls
as
follows
s-
MODE
SWITCH
manual/agc
SWITCH
RF
GAIN
CONTROL
IF
GAIN
CONTROL
AF
GAIN
CONTROL
MUTING
SWITCH
MONITOR
SPEAKER
SNITCH
IF
INPUT
SWITCH
"CW"
(initial
setting)
.
"MANUAL"
.
Minimum.
Maximum.
Maximum.
"OFF"
.
"ON".
"ON" (dolly
down).
First
tune
the
signal
generator
to
10.
7
MHz by
zero-beating against
the
crystal-
controlled
beat
oscillator
(receiver
running
in
"CW"
mode
and
generator
modulation
switched
off).
Setting
accuracy
will
be
within
1
kHz,
so
permitting
accurate
adjust-
ment
even
in
the case
of
a
non-standard
receiver
fitted with
a narrower
crystal
filter
than
that
normally
used.
Apply
modulation
(30
°/o
y
400
Hz)
to
generator,
set
receiver
MODE ST/ITCH
to
"AM"
and
adjust
the
attenuator
for
a
reading
of
approximately
50mW
on
the
output meter. Peak
the
single
cores
in
T
6,
T7
and
T8
for
maximum
output,
tuning
in each
case
to
the upper
peak.
Repeat
these
adjustments
and
then
set
the attenuator
for
a
precise reading
of
50mW
output
(external
speaker
disconnected).
Sensitivity should be
of
the
order
180pV
.
If
sensitivity
should
appear
to
be low,
introduce
the generator at the
bases of
TR16
and
TR17
in
turn,
with
O.OOlpF
blocking as
before.
Check input
required for
50mW
output using
the
following
figures as
a
guide.
Allow
for
some
variation
above or
below
the
figures
quoted
to
cover
transistor
spread
etc.
Generator
applied
at
base
of
TR16
. .
.
.
600|iV
for 50mW output.
Generator
applied
at
base of
TR17
.
.
.
.
3.6mV
for 50mW
output.
If
sensitivity
is
low
from
TR17, check
audio
sensitivity on the
high-level channel
with
a
1000
Hz
signal
applied
across
the
AF GAIN
CONTROL.
With
this control at maximum
setting,
an
input
of
1.7mV
should
produce
an
output
of
500mW in
30.
Re-alignment
of
the
FM
IF Channel
.
Test
Equipment
As
for
alignment
of
the
AM
IF
Channel.
Connect
generator
and
output meter as
for
alignment
of the AM
Channel?
tune
to
10.
7
MHz
by
reference
to
receiver
beat
oscillator.
Locate
D5
(at
front
left-hand side
of
main
IF
board)
and short with
a
temporary
wire
strap
soldered
to
the
underside of
the
printed
board.
This allows the
standard
AM
generator
to
be
used
for
alignment.
The
built-in
tuning meter
should
be ignored
during
the
early
part
of
the
alignment
procedure.
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