10-2 Operational description
The block diagram
of
the
power
supply
unit
is shown
above.
lt
adopts the self-excitation ON/ON control
method. First, the source
supply
is rectified
through
the
noise
filter and converted
into
direct current. As the de
current is
applied
to
the switching transistor,
it
causes
the
transistor
to
start repeating ON and
OFF.
After
the
de
voltage is converted
into
high frequency pulse,
it
is
added to the
primary
side
of
the main
transformer
which
causes
to
induce voltage on
the
secondary side.
This high frequency
pulse is then rectified and filtered to
obtain the de
voltage
of
+5
volts. For control
of
output
voltage, the
output
voltage is compared
with
the refer-
ence voltage and its
error
is detected in the control
section.
While
the switching transistor is in the
OFF
cycle,
it
makes
the
photo
cuppler
PC1
active
by
the
detecting
signal
of
the control section
for
given period.
By adjusting
control current
of
the
drive circuit,
it
makes
the
out
put stabilized.
10-3 Maintenance
Cleaning
Dust deposit inside the
power
supply
unit
may
becomes
the
cause
for
overheat
as
it
prevent heat dispersion,
which
results in damage in component. Stains on the
fuse contact and connector
contact
may
lead to contact
failure.
So,
it
has to be cleaned using soft cloth dam-
pened
with
alcohol
or
dry
soft cloth.
10-4 Problem determination and sequence
Follow the next procedure
to
find the cause
of
trouble.
(1)
Avoid removing the board to check. But visually
observe the board
to
check
for
open circuit line,
burnt
resistor, fuse, and semiconductor chips in the
first
place.
(2)
If
a defective item were found,
it
has
to
be replaced
with
the
new
one. But, care
must
also taken
as
there are possible defects in
multiple
number
of
components.
34
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