Fisher 700-T - Service Procedures; Power Amplifier Testing and Measurement; Dial Stringing and Adjustment; Lamp Replacement Procedures

TESTING
THE
POWER
AMPLIFIER
CAUTION
DO
NOT
use
uninsulated
clips
on
any
connection
except
to
the
-
chossis.
Always
use
miniature,
insulated
clips
when
connect-
ing
to
component
leads,
socket
lugs
and
terminal
strips—it
tekes
only
a
fraction
of
a
second
to
destroy
a
transistor
with
an
accidental
short
circuit.
Make
sure’
metal-cased
instruments
are
not
touching
the
chassis
directly
or
through
other
instru-
ments
and
commoneground
leads.
:
WARNING:
Disconnect
AC
power
cord
while
removing
or
ine
serting
transistors.
‘
@
Remove
transistors
Q1
to
Q4,
QB}
to
Q804
and
Q851,
Q852
and
Q853
(both
channels)
from
their
sockets.
Lobe!
each
tran-
sistor
with
its
location
in
the
unit.
©
Set
VOLUME
control
to
its
minimum
position
(extreme
count-
erclockwise).
6
Set
line
voltage
through
an
adjustable
transformer
to
7
VAC.
Plug
in
AC
power
cord.
e@
Connect
common
lead
of
DC
VTVM
to
the
chassis.
@
Measure
voltage
ocross
filter
capacitor
C19
or
at
the
Bt
terminal
of
the
bridge
rectifier;
reading
should
be
between
60
and
66
YDC.
:
@
Measure
voltage
at
junction
of
resistor
R50'ond
zener
diode
CR2;
reading
should
be
between
11.5
and
12.5
VDC.
@
Meosure
voltage
at
junction
of
resistor
R51
and
zener
diode
CR
3;
reading
should
be
between
23
and
25
VDC.
@
Insert
left
channel
predriver
transistors
Q801
and
Q803
(Q802,
Q804—right
chonnel)
in
their
sockets
on
the
predriver
board.
@
Measure
voltage
at
connection
8F
on
predriver
boord
(BK~
right
channel);
adjust
Output
Adjust
Pot.
R805
(R806—right
channel)
for
reading
of
10
VDC.
-
@
Insert
voltage
driver
transistor
QB51
in
left
channel
driver
board
and
measure
vostage
at
the
collector.
Adjust
left
channel
Center
Voltoge
Adjust
Pot.
RB57
for
a
collector
voltage
of
31
voc.
@
Measure
voltage
from
bose-to-base
socket
terminals
of
power
driver
transistors
Q852,
Q853
on
left
chonnel
driver
board.
Ad-"
just
left
channel!
Output
Bias
Adjust
Pot.
R858
for
reading
of
2.3
VOC.
@
Insert
left
chonne!
power
driver
transistors
Q852,
Q853
in
their
sockets.
@
Measure
voltage
at
connection
8H
on
left
channel
driver
board;
reading
should
be
between
28
and
34
VDC.
@
Insert
left
channel
power
tronsistors
Q3,
Q4
(Q1,
Q2-right
channel).
@
Moosure
voltage
across
resistors
R37
and
R39
(R38
and
R40~
right
channel);
reading
should
be
between
35
and
50
mV
across
each
resistor.
:
NOTE:
VTYM
must
have
a
25-volt
or
lower
full-scale
range
to
make
this
reading
properly.
@
Repeat
preceding
steps
for
the
right
channel.
INTERMODULATION
DISTORTION
TEST
e
Set
BALANCE,
BASS
and
TREBLE
controls
to
their
center
positions.
Set
MODE/TAPE
MONITOR
switch
to
left-hand
STEREO
position,
SELECTOR
switch
to
AUX
and
SPEAKERS
switch
to
MAIN.
Set
LOUDNESS
CONTOUR,
LOW
FILTER
and
HIGH
FILTER
switches
to
OFF.
Unplug
AC
power
cord.
@
Connect
9
4-ohm,
50-watt
resistor
across
the
LEFT
:
SPEAKERS
MAIN
terminals.
In
paralle!
with
the
load
re-
sistor,
connect
the
input
leads
of
an
[M.(fnter-Modulation)
distortion
onalyzer
and
the
leads
of
an
AC
VTVM
capable
of
reading
0.1
volts
with
accuracy.
SERVICE PROCEDURES
©
Conhect
|M-analyzer
generator
output
to
the
LEFT
AUX
LOW
input.
i
NOTE:
Speaker
common
terminals
are
not
af
ground
potential.
IM
distortion
onalyzer
ground
should
be
connected
to
AUX
input
ground
only.
:
e@
Connect
AC
power
cord
and
rotate
VOLUME
control
to
its
maximum
clockwise
(full
volume)
position.
@
Increase
IM-analyzer
generator
input
to
amplifier
for
30
watts
output
(9.0
VAC
across
4-ohm
foad
resistor).
AFTER
ONE
FULL
MINUTE
OF
WARM-UP
TIME,
PROCEED
TO
NEXT
STEP.
NOTE:
Warm-up
timeis
very
important
in
obtaining
proper
readings.
The
characteristics
of
transistors
change
slightly
os
their
internal
temperature
rises.
Once
the
transistors
are
worm,
the
tests
should
be
completed
without
delay
—before
they
can
cool
off.
:
@ IM meter reading should be 0.8% or less.
@
Repeat
preceding
steps
for
the
right
channel.
NOTE:
If
any
of
the
preceding
instructions
are
different
from
from
those
supplied
with
the
IM-analyzer
instruction
manual,
it
is
best
to
follow
those
in
the
manval.
If
a
load
resistor
of
50-watt
rating
is
built
into
the
IM
analyzer,
a
separate
load
resistor
is
not
required.
For
best
results,
the
IM
range
switch
should
be
set
to
give
a
reading
in
the
center
fo
full-scale
portion
of
the
meter
scale
for
greater
accuracy.
HARMONIC DISTORTION TEST
Set
BALANCE,
BASS
ond
TREBLE
controls
to
their
center
positions.
Set
MODE/TAPE
MONITOR
switch
to
left-hand
STEREO
position,
SELECTOR
switch
to
AUX
and
SPEAK-
ERS
switch
to
MAIN.
Set
LOUDNESS
CONTOUR,
LOW
FILTER
ond
HIGH
FILTER
switches
to
OFF.
Unplug
AC
power
cord.
@
Connect
a
4-ohm,
50-watt
resistor
ocross
LEFT
SPEAKERS
MAIN
terminals.
In
parallel
with
the
load
resistor,
connect
the
input
leads
of
a
harmonic
distortion
analyzer
and
the
leads
of
=
-
an
AC
VTVM
capable
of
reading
0.1
volts
with
accuracy.
@
Connect
a
low-distortion
audio
sine
wave
generator,
set
for
1000
Hz,
to
the
LEFT
CHANNEL
AUX
LOW
jack.
@
Connect
AC
power
cord
and
rotate
VOLUME
control
to
its
maximum
clockwise
(full
volume)
position.
@
Increase
generator
input
to
set
for
45
watts
output
(13.4
VAC
across
4-ohm
load
resistor).
Harmonic
distortion
meter
should
read
less
than
0.8%.
_@ Repeat preceding steps for right channel,
POWER
OUTPUT
MEASUREMENT
The
power
output
of
this
unit
is
designed
to
deliver
its
full-
rated
power
with
program
material
(voice
or
music)
into
4-to
16-ohm
loads
for
indefinite
periods.
When
a
constant
1
kHz
(kc)
cudio
tone
is
used
as
a
signal
to
meosure
the
continuous
RMS
power
output,
the
following
pre-
cautions
must
be
taken:
©
Measure
the
power
output
of
one
channel!
ata
time.
©
Limit
the
measurement
period
to
10
minutes
with
a
load
resistance
between
4
and
16
ohms.
If
the
power
output
of
both
chonnels
must
ever
be
measured
simultoneously,
use
a
load
of
4
to
8
ohms
per
channel
and
limit
measurement
toa
period
not
longer
than
1
minute
for
o
4-ohm
load
and
not
longer
than
5
minutes
for
an
B-chm
locd.
BECAUSE
ITS
PRODUCTS
ARE
SUBJECT
TO
CONTINUOUS
IMPROVEMENT,
FISHER
RADIO
CORPORATION
RESERVES
THE
RIGHT
TO
MODIFY
ANY
DESIGN
OR
SPECIFI-
CATION
WITHOUT
NOTICE
AND
WITHOUT
INCURRING
ANY
OBLIGATION.
(225)1S=1276-18
| SERVICE PROCEDURES | .
DIAL STRINGING
©
Turn
the
tension
screw
to
its
mid-position
(Figure
1)
and
remove
the
end
of
the
tension
spring
from
pulley
A
mounting
bracket
(detail
view).
@
Rotate
the
tuning
capacitor
drive
drum
to
its
maximum
clock
wise
position.
Tie
the
end
of
the
dial
cord
to
the
ear
inside
the
top
of
the
drive
drum.
@
Run
the
dial
cord
through
the
slot
in
the
drive
drum
ond
through
the
hole
in
the
chassis
front
ond
under
the
switch
shaft.
@
Wrap
two
full
turns
of
the
dial
cord
around
the
tuning
sheft.
e@
Run
the
diol
cord
around
pulley
A
(Figure
2).
Attach
the
tension
spring
to
hole
2
in
the
pulley
mounting
bracket.
Turn
the
tension
screw
to
its
maximum
clockwise
in
position.
@
Place
the
dial
cord
on
pulleys
B
and
C
and
over
pulley
D.
Position
the
diol
cord
in
the
inner
groove
of
the
drive
drum.
©
Pull
the
dial
cord
taut
and
wrap
2%
turns
around
the
outer
groove
of
the
drive
drum.
Run
the
dial
cord
through
the
slot
in
the
drive
drum
and
under
the
beveled
washer.
Tighten
the
mochine
screw
to
hold
the
dial
cord,
making
certain
that
the
tension
screw
is
in
contact
with
the
screw
stop.
©
Turn
the
tension
screw
counterclockwise
to
hold
the
dial
cord
under
tension
so
that
the
flywhee!
rotates
freely
but
the
dial
cord
does
not
slip,on
the
tuning
shaft.
e@
Place
the
dial
cord over
and
under
the
tabs
on
the
rear
of
the
dial
pointer.
Ploce
the
dial
pointer
on
the
top
of
the
chassis
front
panel.
REPLACING METER LAMP
© Disconnect AC power cord.
@
Remove
the
screws
which
hold
the
top
cover
to
the
chassis
and lift
off
the
top
cover.
@
Gently
push
in
on
the
lamp
and
turn
it
counterclockwise
to
remove.
Remove
the
metal
lamp
shade
and
place
it
on
thenew
lamp
in
the
same
position.
Place
the
new
lamp
in
the
socket,
push
in
gently
ond
turn
it
clockwise
to
lock
it
in
place.
@
Replace
the
top
cover
on
the
chassis
ond
secure
with
the
screws
removed
previously.
REPLACING
STEREO
BEACON
LAMP
@ Disconnect AC power cord.
e@
Remove
the
screws
which
hold
the
top
cover
to
the
chassis
and
lift
off
the
top
cover.
@
Pry
nylon
lomp
holder
from
the
lamp
mount.
Unsolder
the
leads
from
the
lomp
holder.
Solder
leads
torear
terminals
on
the
new
lamp
holder.
Place
new
lomp
holder
in
the
mount.
©
Replace
the
top
cover
on
the
chassis
and
secure
with
the
screws
removed
previously.
REPLACING DIAL LAMPS
@ Disconnect AC power cord.
@ Gently pull all knobs off the front panel control shafts. Re-
move hex nuts from the control shafts and lift off the front
panel.
@ Snap out the defective lamp from the spring clip. Place the
new lamp in the socket making certain that the unpainted side
of the lomp faces the edge of the diol glass.
@ Replace the front panel ond secure with the hex nuts re-
moved previously. Replace the knobs on the control shafts.
REPLACING DIAL POINTER LAMP
@ Disconnect AC power cord.
@
Gently
pull
all
knobs
off
the
front
pane!
control
shafts.
Re-
move
the
hex
nuts
from
the
control
shafts
and
lift
off
the
front
panel.
©
Remove
the
two
foam-cushion
strips
located
at
the
ends
of
the
dial
glass.
e
Loosen
the
screws
that
hold
the
retaining
clips
to
the
diol
glass.
Swing
the
clips
aside
ond
lift
off
the
dial
glass.
© Remove the lamp wires from the holding clip on the rear of
the pointer base and from the two clips on the top of the
chassis.
@ Slide the dial pointer assembly directly downward to release
it from the pointer base. Slide the new dial pointer assembly
upward, while pressing downward on the pointer base, until
the tab on the pointer motes with the slot in pointer base.
© Twist the lamp wires together and ploce them under the
holding clip on the rear of the pointer base. Do not leave any
slack in the wire above the pointer.
©
Connect
the
ends
of
the
two
wires
to
the
clips
on
the
top
of
the
chassis.
@
Replace
the
dial
glass
and
position
it
down
and
towards
the
left
of
the
chassis
front.
Swing
the
retaining
clips
back
into
place
and
tighten
the
retaining-clip
screws.
Replace
the
foam-
cushion
strips.
@
Replace
the
front
panel
and
secure
with
the
hex
nuts
removed
previously.
Replace
the
knobs
on
the
control
shafts.
CLEANING DIAL GLASS
@ Disconnect AC power cord.
©
Gently
pull
all
knobs
off
the
front
pane|
control
shafts.
Re-
move
the
hex
nuts
from
the
control
shafts
and
lift
off
the
front
panel.
@
Remove
the
two
foam-cushion
strips
located
at
the
ends
of
the
dial
glass.
©
Loosen
the
screws
that
hold
the
retaining
clips
to
the
dial
glass.
Swing
the
clips
aside
ond
lift
off
the
dial
glass.
@
Remove
dust with
o
dry
cloth.
If
you
wish
to
clean
more
thoroughly,
use
a
soap-and-water
solution
only,
any
stronger
agent
may
damage
the
markings
on
the
glass.
@
Replace
the
dial
glass
and
position
it
down
and
towards
the
left
of
the
chassis
front.
Swing
the
retaining
clips
back
into
place
and
tighten
the
retaining-clip
screws.
Replace
the
foom-
cushion
strips.
@
Replace
the
front
panel
ond
secure
with
the
hex
nuts
re-
moved
previously.
Replace
the
knobs
on
the
control!
shafts.
CLEANING FRONT PANEL
WARNING:
Use
only
plain
lukewarm
water
ond
a
freshly
loundered,
soft
lint-free
cloth
to
clean
the
front
contro!
panel.
tem ene,