Advertisement
TROUBLE-SHOOTING PROCEDURES
Connect
a
phonograph and
speaker
to
the amplifier
as
de-
scribed
in
"Electrical
Connections" and
set
controls
for
phono
listening.
Play
a
known
high quality LP recording
on
the
phonograph.
If
there
is
no output
to
the
speaker
or
if
the output
is
low
or
audibly
distorted,
procede
to
the
checks
for
those
symptoms.
If
there
is
excessive
hum
in
the output,
disconnect
the
phono
input
cable from
the
amplifier
and
short
the
phono
input jack
to chassis.
If
the
hum
disappears,
the trouble
is
not
in
the amplifier but
in
the
phonograph
or
in
the
connection
to
the amplifier.
The cause
of
phonograph
hum
maybe
a
metal pick—
up arm
not
grounded
to
the
cable
shield
(try
a
good
single
ground
connection
to
the
cable
shield
from
turntable frame,
pick-
up arm, and
cartridge case), direct
hum
pick-up by
the
magnetic
cartridge from the record player
motor
(try
using
a rubber
mat on
the turntable
to
Increase the separation of
the
pick-up
from the motor),
or
pick-up
from a
power
trans-
former or other
magnetic
field in
the vicinity
(try
moving
phonograph
away
from suspected
source).
Check
also that
the
phono
input
cable
shielding
is
grounded
to
the
ampli-
fier
chassis
atone
pointonly, through the
skirt
of the input
connector
where
it
plugs
into
the amplifier.
Finally,
try
a
good
building
ground such
as
a
connection
from a cold
water pipe terminated under speaker
terminal
"G"
on
the
amplifier.
Do
not
connect
such a
ground wire
to
other
components
in
the system.
Excessive
hum
on
other
inputs
maybe
checked
in
a
similar
manner. Disconnect
the input
cable
in
question
and
short
the particular input jack
to
the
chassis,
if
the
hum
dis-
appears, the trouble
is
external
to
the amplifier.
Note
that
on
all
inputs,
the braid of the input
cable should
con-
nect
to
the amplifier
only through
the
skirt
of the input
connector.
The cause and
remedies
for
the
following
symp-
toms are then based
on
the
assumption
that
checks
made
in
the
manner
described
above have
eliminated
the
possibility
of the trouble
being
external
to
the amplifier.
If
the trouble
is
no
output
or
low
output,
check
AC
signal
voltages
and
DC
operating voltages
starting at
the Input
and working step-by-step toward
the output.
Set the
VOLUME
i LOUDNESS
controls
to
maximum
(10),
the
BASS
and TREBLE
controls
to
their
mid-points (0),and
the
SCRATCH & RUMBLE
filters
to
OFF.
Use
a
1000 cycle
sinewave
signal,
such
as
supplied
by
theEiCO
377
Sine
&
Square
Wave
Audio
Generator,
In
addition, use a pre-
cision
100:1
attenuator
to
permit obtaining a
level of
0.005
volt fed into
MAG.
PHONO
from
an audio gen-
erator
output
of
0.5
volt,
which can
easily
be measured
on
the lowest
AC
volts
range
of
your
VTVM
(also
improves
signal
to
hum
from generator).
Use
a high Input
impedance
VTVMforall
AC
signal
voltage measurements
and
a
VTVM
or 20,
000
0/
volt
VOM
for
DC
voltage measurements.
If
the trouble
is
an excessively
distorted
output,
try
tube
replacement,
signal tracing, or
procede
directly
to
voltage
and
resistance
measurements.
When
the
defective
stage
is
localized,
procede
to
a
resist-
ance and
voltage
check
of the stage, using the data
In
the
VOLTAGE
and
RESISTANCE
chart.
Disconnect
the
ampli-
fier
from
the
power
line
and
discharge capacitors
prior
to
making any
resistance
check and
prior
to
removing any
or
all
of the
EL84 output
tubes.
Do
not
turn
the amplifier
or\
with
any
of the
output
tubes
removed
.
CHECKING
A
TYPICAL TUBE
STAGE
1.
Check
tube.
2.
Check
plate
and cathode
resistor.
3.
Check
couf^lng capacitors
for
leakage
or short.
4.
For
output
stage,
check dc
resistance of transformer
windings.
5.
Check
grid leak
resistor for
open.
6.
Check
cathode by-pass
capacitors
for short.
7.
If
no
or
low B+ voltage on
tube,
check decoupling
path
for
open
or
defective R40, R41,
R42 and
filter
capac-
itor
C31
or
C32.
8.
If
wiring
and
circuit
components
including the tube
check
O.K.
and
B+ voltage
is
excessive,
check
the
de-
coupling path
for
short or
defective R40, R41, R42.
Suspected
trouble
in
the equalization, tone,
filter,
and
volume
or
loudness controls
and
networks should
lead
to
specific resistance
and capacitance checks
to
localize the
trouble.
In
general,
if
the user suspects
poor frequency
response,
defective equalization,
or
defective operation
of the
tone
controls or
filter
circuits,
the amplifier should
be
tested
thoroughly with audio generator, vtvm,
and
scope.
SERVICE
If
trouble
developes
in
your
instrument
which you
can
not
remedy
yourself,
write
to
our
service
department
listing
all
possible indications that
might be
helpful.
If
desired
you
may
return the
instrument
to
our factory
where
it
will
be placed
In
operating condition
for
$9,50
plus the cost
of parts
replaced
due
to
their
being
damaged
in
the
course
of construction.
NOTE:
Before returning
this
unit,
be
sure
all
parts
are securely
mounted.
Attach a
tag
to
the
instrument, giving
your
home
address
and
the trouble
with
the
unit.
Pack
very
carefully
In
a
rugged
container, us-
ing
sufficient
packing
material (cotton,
shredded
news-
paper, or
excelsior),
to
make
the unit
completely
immov-
able within
the container.
The
original
shipping carton
is
satisfactory,
providing the
original
inserts
are used
or
sufficient
packing
material inserted
to
keep
the
instru-
ment immovable.
Ship
by prepaid Railway
Express,
if
possible,
to
Electronic Instrument
Co.
,
Inc.
,
33 "00 North-
ern
Blvd.,
Long
Island
City
1,
New
York.
Return ship-
ment
will
be
made
by
express collect.
Note
that
a
carrier
cannot be
held
liable
for
damages
in transit
if
packing
IN
HIS
OPINION,
is
insufficient.
Advertisement
Troubleshooting
