Page 90
Heathkif
If
you
still have not located the trouble
after
the
"Vi-
sual Checks"
are complete, and a voltmeter is avail-
able, check voltage
readings against those shown on
the Schematic.
Read the "Precautions for Trouble-
shooting" before you make any measurements.
NOTE: All
voltage readings were taken with a high
impedance
voltmeter. Voltages may vary as much
as ±20%.
NOTE:
In
an
extreme
case where
you are unable
to
resolve
a difficulty,
refer
to
the
"Customer
Service"
information
inside
the
rear
cover of
this Manual.
Your
Warranty
is located
inside
the
front cover.
PRECAUTIONS FOR
TROUBLESHOOTING
1. Use caution when you test IC and transistor
circuits. Although they have almost unlimited
life when
used
properly, they are much more
vulnerable to damage from excessive voltage
or current than other circuit components.
2. Be
sure
you do not
short
any
terminals
to
ground when
you make
voltage
measure-
ments. If
the probe
should
slip,
for
example,
and
short across
terminals
or voltage
sources,
it is very
likely
to cause
damage
to one
or
more IC's,
transistors,
or diodes.
CHECKING
TRANSISTORS AND
DIODES
SILICON
BIPOLAR
TRANSISTORS
To check
a transistor accurately,
you should
use a
transistor
tester.
However, if
one is not available,
you can use an
ohmmeter to determine
the
general
condition of
any one of the
bipolar
transistors in
this
kit. The
ohmmeter you
use must have
at least
1
volt
DC at the probe tips
to exceed
the threshold
of the diode
junctions in the
transistor
you are test-
ing.
Most vacuum
tube voltmeters meet
this require-
ment.
To
check
a
transistor
with an
ohmmeter,
proceed
as follows:
same,
but may be
either
high or
low. If one
reading is
high and
the
other low, the
transis-
tor
should be
replaced.
(Use the
Identification
Chart on Page
102 to
identify
the
transistor
leads).
4.
Interchange the
test leads
and
repeat step
3.
NOTE: In the
unusual case
when the
readings
are
all low,
or all high,
no
matter
which
ohmmeter lead
is
connected
to the
base, thej
transistor
should be
replaced.
MOSFETS
1. Remove
the transistor from
the circuit.
2.
Set the ohmmeter
to the R
x
100 range.
3.
Connect one of the ohmmeter
test
leads
to the
base (B) of
the transistor. Touch
the other
meter lead
to the emitter
(E) and then
to
the
collector
(C).
Both
readings
should be the
An
insulated
gate type MOSFET is used
at
Q107
on
the
oscillator circuit
board. Usually, any
defect in
these devices
is an internal short circuit
between
the source
and one of the
gates.
You
can check
them
in the
circuit with a high impedance
voltmeter
(10
megohms
or higher). An abnormally
low source volt-
age may indicate
an
internal
short circuit.
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