QEI 675 - Power Amplifier Alignment

www.SteamPoweredRadio.Com
NOTE:
BE
SURE
OF
THE
ACCURACY
AND
STABILITY
OF
THE
COUNTER.
b.
Remove
all
modulation
from
the Exciter.
If
any
modulation
is
pre-
sent,
it
is
necessary
for
the counter
to
have
a gate time
of
at
least
four seconds in order
to
obtain a
correct
reading.
c. Set
FREQ
ADJ
pot
R2
to
the
center
of
its
range.
d.
Adjust
A2C27
until
Exciter
is
on
frequency.
e.
Vary
FREQ
ADJ
pot
R2
from
end
to end. Frequency should vary app-
roximately+
500
Hz.
Reset Exciter
on
frequency.
5-3
POWER
AMPLIFIER
ALIGNMENT
1. Coarse Alignment
a. Connect a
power
meter capable
of
displaying
25W
to
the
RF
OUT
jack
Jl located
on
the
rear
panel
of
the
unit.
Connect a signal
samp-
ling
probe to the output
of
the
power
meter. Connect a spectrum
analyzer
to
the probe. Connect a
50
ohm
dummy
load
to
the output
of the signal sampling probe.
Be
sure
that
the
power
meter
and
dummy
load are designed
for
use
at
FM
broadcast frequencies.
b.
Apply
power
to
the
unit
and
observe
pilot
lamp
CR2
and
AFC
LOCKED
lamp
DSl.
If
lamp
does
not illuminate
refer
to
FMO
alignment pro-
cedure.
c. Set
PWR
ADJ
control
Rl
full
clockwise. Set the
MULTIMETER
switch
S2
to the
IPA
position.
Set
A3C2
to mid-range.
d. Observe
an
indication
of
IPA
collector
current
on
the multimeter.
Maximize
this
indication
by
adjusting
A2C6
and
A2C7
of
the
A2
board.
e. Set the multimeter switch
to
the
PA
position.
for
a
maximum
reading in
this
position.
f.
Set the multimeter switch
to
the
RF
position.
A3Cl5
for
a
maximum
reading in
this
position.
is
now
complete.
2. Final Alignment
Adjust
A3C7
and
A3C8
Adjust
A3Cl4
and
The
coarse alignment
a. Set
MULTIMETER
switch
S2
to
the
RF
position.
Adjust
A3Cl4
and
A3Cl5
for
maximum
reading
on
the multimeter.
If
the
Power
Amp-
lifier
draws
excessive
current
and
trips
the
power
supply overload
circuitry,
adjust
A3Cl5
clockwise
until
this
condition
is
corrected.
When
this
condition appears, the output
power
is
in excess
of
20
watts. Adjust
A3Cl5
clockwise to reduce the output
power
to
20
watts. Readjust
A3C14
for
a
maximum
reading
on
the multimeter.
-16-