Eico HF-12 Instruction Manual page 7

connection
to
the
cableshield 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 at
one
point only 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
may be 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
thaton
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
control
to
maximum
(10),
and
the
BASS and
TREBLE
controls
to their
mid-points
(0).
Use
a
1000 cycle
sinewave
signal
,
such
as
supplied by
the
EICO 377
Sine
&
Square
Wave
Audio
Generator.
In
addition, use a pre-
cision
100
: 1
attenuator
to
permit obtaining a
level of
0.01 volt fed into
MAG.
PHONO
from an audio generator
output of
1
.0 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
VTVM
for
all
AC
signal voltage
measurements
(such as the
EICO
232,249,221,
or 214)
anda
VTVMor20,000Q/voltVOM
for
DC
voltage measurements.
If
the trouble
is
an excessively
distorted
output,
try
tube
replacement,
signal tracing,
orprocede
directly
to
voltage
and
resistance measurements.
When
the
defective stage
is
localized,
proc^deto
a resist-
ance and voltage check
of the stage, using the data
In
the
VOLTAGEand
RESISTANCE
chart.
Disconnect the ampli-
fier
from the
power
line
and
discharge capacitors
prior to
making any
resistance
check and
prior
to
removing
either
or
both of the EL84 output tubes
V4
and V5.
Do
not turn
the
amplifier
on with
either of the
output
tubes
removed.
TROUBLE-SHOOTING
A
TYPICAL TUBE
STAGE
1
.
Check
tube.
2.
Check
plate
and cathode
resistors.
3.
Check
coupling 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 R18, R31
,
R32, R33 and
filter
capacitor
C17
or
C18.
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 R18,
R31
,
R32, R33.
Suspected
trouble
In
the
equalization, tone, and
volume
controls
and networks should lead
to specific resistance
and capacitance checks
to
localize
the trouble.
In
gen-
eral,
if
the user suspects
poor frequency
response,
defec-
tive
equalization, or defective operation of the tone
con-
trols,
the amplifier
should be
tested
thoroughly with audio
generator,
vtvm, and scope.
SERVICE
If
trouble
develops
in
your instrument
which you can not
remedy
yourself, write to
our service department
listing
all
possible indications that might be helpful
.
Note
num-
ber
appearing
in
red
under
the
word "Manual"
on the front
cover.
If
there
is
no number,
state
this.
If
desired,
you
may
return the instrument to
our factory
where
it
will
be
placed
in
operating condition
for $7. 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
theunit.
Pack very
carefully
in
a
rugged container, using
sufficient
packing
material (cotton,
shredded newspaper,
or excelsior),
to
make
the unit
completely
immovable
within the container.
The
original
shipping carton
is
sat-
isfactory,
providing the original
inserts
are usedor
suffi-
cient
packing
material
is
inserted
to
keep
the instrument
immovable. Ship
by
prepaid Rai
Iway
Express,
if
possible,
to
Electronic Instrument Co.
,
Inc.,
33-00
Northern Blvd.
Long Island City
1,
N.
Y. Return shipment
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.
6