48
-
~
- - - ~
HEATHKIT
=AG®iMMH
STAGE-BY-STAGE
SIGNAL
INJECTION
This section
of
the
Manual
consists of
a
series
of
hum
tests
that
will help
you
locate the area of the
difficulty.
The
hum
is
injected
into the
circuit
when
you
touch the
circuit
with a narrow-
bladed screwdriver.
CAU'l'ION:
FuU
AC Zine v
oltage
wiU
be
present
at
s
everal
places
in
the
Amplifier
when t he power
cable
plug
is
connected
t o
an
AC
outlet.
Be
especially
careful
that
you do
not
touch
the
AC
so
ck
e
ts,
power
switch
lugs,
or
fuseh
o
ld
er
lugs.
Use
a narrow-bladed screwdriver or other
narrow
metal
object
for these
tests.
Hold
the screwdriver with your finger
touching the metal
shaft;
then touch
the
circuit
at
the place
specified
in
the
chart.
Touch
only the point
listed.
If
a high
impedance
input voltmeter
is
available,
'
it
may
be
helpful to
compare
the voltage readings in the area
of
trouble with the
correct
readings
indicated
on
the Schematic
and
1oltage
Charts.
Be
sure to
remove
the
power
cable plug
from
the
AC
outlet
before
you
make
any
repairs
on
the Amplifier.
Refer to the
11
Ci
rcuit
Board
X-Ray
Views
11
(Page
61)
and
to the Schematic (fold-out
from
Page
65)
to
locate
and
identify
the
parts
that
may
be
listed
on
the
charts.
Each
signal
injection
chart contains
duplicate information for the
right
and
left
channel
circuits.
If
you
are
having
difficulty
in
only
one
channel
in your Amplifier, disregard
that
part
• of each
chart
that
deals with the
other
(working) channel.
FINDING THE AREA
OF
TROUBLE
NOTE:
If
you
have
trouble only
when
operating in the
Phono
mode,
disregard
the following information
and
proceed to
the
11
Phono
Preamplifier Signal Injection
Chart"
on
Page
50.
( ) Connect a
set
of speakers to the
Speaker terminals
(refer
to fold-
out
from
Page
43).
( ) Set the controls
and
switches to the
following
positions.
Volume:
Centre
of
rotation
Balance: Centre of
rotation
Aux
pushbutton:
ON
Speaker pushbutton:
ON
All
other pushbuttons:
OFF
( )
Push
the
Power
pushbutton on.
......
L-,
L..
w
L....·
To Next Page
Loading...
Need help?
General
