Technical information

O
RADIO
RETAILING?S
rrSenuie
ZENITH
5528
Dead
or
rveak
on automatic tun-
ittg
check C2,
a
50 ntmf. con-
denser
for
open
(part
No.22-289)
ZENITH 56,t7
Blown ballhst
tube before
re-
placing
tube check C9,
a 4O
mfd
con-
denser
connected to cathode of.2526.
If defective,
replace.
ZENITH
565'
Excessive
regeneration
.
nrove
grid
lead of l2A8G
away fronr oscilla-
tor section of
gang
condenser.
ZENITH
570{
Oscillation disconnect
6K7
first
audio from mutual bias system.
Insert
3500
ohm
I
watt
resistor
by-
passed
with
25 mfd
condenser in cath-
ode circuit.
Connect
grid
return
to
chassis.
ZENITH
57I,I
Whistles at medium volume, noisy
between signals . . .
Open
filter con-
denser; loose connection
or open con-
denser
across
r.f. choke.
ZENITH 57I,t
Inoperative on
automatic
tuning
.
open
compensating
coil
(part
No 20-196, No. 3 in diagram)
ZENITH
57I,I
Automatic
tuning dead or noisy
.
. .
dirt on
contacts or warped contact
strip
shorting to
ground;
also,
look
for
shorted
compensating condenser.
zENfTH
5721, E72S
Noisy on automatic tuning
washer
on latch bar of
pushbutton
assembly
grounding;
poor
contact
on
band
switch.
Signals cut
out above 1400 kc.
5
megacycle
trimmer screwed in too
tight.
Oscillation
open screen by-
pass; grid
lead of
6K7
near a.v.c. lug
or
plate
lead
of 6A,8; wave trap open
or improperly
adjusted.
zENtTH
580t,
t004
Reduced
volume,
shadowmeter
does
not
function
. shorted
.05
mfd
by-
pass
on
r.f.
input
side of
6C5 shadow-
nreter
grid.
zENtTH
5808, t005,
lt03
Oscillation
at 550 kc. improper
adjustment
of
wave
trap; realign
trap.
Noisy
tuning
grounding
braid
on
gang
rubs
on
flywheel; burrs
on
drive
shaft shorting
to
volume con-
trol: dial
pulley
rubbing
against dial.
66
zENITH'5902
Oscillation
or audio
howl.
ground
the 56 detector
cathode right
at
the
socket, remove
original
black
ground
wire.
Reroute
the second i,f.
plate
wire from
the lug
around
the 8
rurfd
condenser
and
connect
to the
other side
of the choke.
ZENITH 5907
AND I2O7
Distortion,
sounds
very
much
like
blocking a.v.c.
action look
for
open
filter
condenser section.
zENITH 75232
oscillation
when
volume
ts
.
check
Cl9
a 12 mfd
for open.
of the chassis and holding
the motor
assembly. The
motor assembly
should
be
moved
in the elongated
holes
until
the drive belt
has
a
snug tension but
not
too tight an
action. Then retighten
the
hexagon mounting bolts.
If
the drive
mechanism
has a
ten-
dency
to
slip when
using the large
man-
ual
knob check
for
a
loose
spring clutch.
All
adjustments
to
the clutch
should
be
mlds
very
carefully. The mechanism
being essentially
the
same as in
1937.
Adjustments
are made
by
turning
the
screw mounted
through the
blue
steel
clutch
spring found
at the front
of
the
brass drive
shaft
mechanism.
By run-
ning
the
screw
in,
the action will be
tightened,
and by
running
the
screw
out,
the
action
will be
loosened,
but in
all
cases
only one or two complete
turns
should
be necessary.
All
bearings,
dial
mechanism
and
gears
of
the
gani
should
be lubricated
approximatcly
once a
year.
If at any
time
it is necessary
to change the
elec-
tric
eye tube,
care should
b€
taken
not
to
place
the
tube
too
far
forward
as this
will
cause
a strain
to be
placed
on
the
dial pan
causing
friction
at the center
hub
of
the
gang
shaft
and
the motor
assembly
will nqt
operate
freely.
ZENITH
I937 MODELS
Electric
tuning
service adjustments:
Make
sure
that nothing
is
obstructing
the
free
action of either the
belt,
the
pulley,
or the
drive
shaft, such as wires
or
component
parts.
Check the
band
change shaft for
clearance
on the
9-12-15
tube models.
The
die
cast bracket through which
thc
brass
drive
shaft
for the motor
travelr
can be
centered
properly
by loosening
the
two
Parker-Kalon
screws which
hold
the
bracket
to the
front
of the dial
assembly.
After
centering
the
above
mentioned
die
cast
bracket
retighten the
two Parker-Kalon
screws.
Check
the
ft
nut
at the
rear
of
chassis
in
this
manner; loosen the
nul
permit
the
motor to run
and
retighten
the
rt
nut
while
in operation. This
will
allow the
front
and
rear
bearings
to
align
themselves properly.
Check
for ample
clearance between
the
dial
gang
drive
pulley
and the
mounting
nut
for the bearing
through
the
front
of the
chassis approximately
sl"
clearance. Brass
drive
shaft
should
also
have
ample clearance
at rear
of
chassis
between
collar
mounted
on
motor
switch.
The large
drive pulley
mounted
on
the
rear
of
the
brass shaft
should
be
in
line
with
the small
pullev
which
will
be
found
mounted
on
the
motor
armature.
Alignment
can
be accom-
plished
by loosening
the two
set screws
and sliding
the large pulley
either
back-
ward
or forward
on the
brass
shaft.
Audio
advanced
condenser
ZENITH
'37
Scratchv
noise
on
trrning
flywheel
rrrorlels
.
.
.
flywhceJ rrot
making proper
grouncl
at end of shaft. Tighten
spring
rrt
end of shaft by moving
pulley torvards
center; oil.
ZENITH 1937
5
AND
t TUIE MODELS
Lor.r'
sensitivitl
and volunre, broad
tuning increlsed
resistance
in
pt'i-
mary
w'indings
of i.f.
transf ornrels.
Resistance
varies
f
rom the normal
6
ohm to
as
high
as 90
or 3000
ohnrs.
Replace
all
i.f.
transfornrers for per-
manel)t repalt.
ZENITH
I937
MODELS
On
the
8,
l0
and 12 tube
model
1937
Zenith
sets,
difficulty
is
sometimes en-
countered getting
optimum
tracking
over
all
bands.
Generally
the B
band
is
the one
giving
the
most
trouble,
and
as
this is
the key ltand
around
which
all
the fundamental
calibrations
of
the
other
bands
are
obtained, its
importance
in
the alignment
procedure
is
obvious.
The
fault
lies in
the
shifting
of the
inductance
in the
tapped first
detector
coil. The
consequent
mismatching
of
the
inductive-capacitive
clesign
results
in
the
shifting
of
the
pcak
resonant
condition
for
optimunr
alisnmcnt
of the
circuit. In
other words,
clrre
to
the
poor
matching
of
inductances
as
a
result
of
this
shift, a
resonance
peal<
could
not
be obtained
in the R.F.
tuned
circuits.
Ffowever,
the
remedy
for
this
is
rather
easily
obtained.
It
has been
found
that shiftins
the.small
fixed mica
conclenser
marked
Cl in
the
diagram,
ordinarily
connccted
in
the
grid
circuit
of
the antenna
coil
secondarv.
over to
the
first
detector
coil
circuii
in the
identical position,
the matching
of
the
coils
becomes
closer
and a consequent
iurprovement
in
sensitivity
is
obtained.
'fhe-
capacity
oi this
conclenser
is 5
nlm
t(ls.
The tension of the
drive
belt
for
the
motor can be
adjusted
by
loosening the
two hexagon
bolts
found
at
the rear