Service manual
The
Power
Supply
CIRCUIT
THEORY
CR26
_::-::-::-:4
A:-'I/SO
V
or
1.S
AlSO
V
on
h.~t
sink
~-r:----r-:U)"""':::::
+5
V
N
I'"
",I
-.
uu
o"ai
L---~~~-+-~~-~---;uD
.
+.
RS
lO
k
C7
6800
SOV
+5V
GND
1--+_..::::::.+26
v
+26 V
GND
The
Power
Supply
generates
two
outputs,
+ 5VDC and +
26VDC.
Both
outputs
are regulated. The
5VDC
output
supplies
the
microprocessor and TTL circuits. The +
26VDC
output
supplies
the
print
wire
coils and
the
paper feed and carriage
motor
drive circuits.
+
5VDC
Supply
VR 1 is a series regulator. The series regulator keeps
the
output
voltage
constant
when
the
load varies.
Capacitive filtering eliminates
most
of
the
ripple voltage on
the
output.
CR26 is a full
wave
bridge
rectifier
which
converts
the
AC
voltage
generated
from
the
top
secondary
winding
of
the
power
transformer
to
DC voltage.
+
26VDC
Supply
A
shunt
type
regulator
circuit
generates
the
constant
26
VDC
output.
UNREG
DC
+26
VDC REGULATOR CIRCUIT
R7
023
,=-
.7V
27V
VOUT
=019
VBE
+ VCR23
26.3V
=
-.7V
+27V
+26
VOLT OUTPUT
~
C1
J
ILO
AD
The
output
voltage
is regulated
at
26.3VDC
because
the
base
to
emitter
voltage
of
019
opposes
the
voltage
developed across CR23.
Most
of
the
load
current
passes
through
the
power
transistor
023.
CR27 is a full
wave
bridge rectifier
which
converts
the
AC
voltage
output
from
the
bottom
secon-
dary
winding
of
the
power
transformer
to
DC voltage.
C7
filters
the
rectified DC
output
voltage.
7