Commodore C64 Service Manual page 6

There are three versions of the C64,
The C64
with
a
five pin
connector video output {326106),
The C64
with an eight pin
connector video output {251
1
38},
and the
C64B which has improved
system clock
circuit
design (251469).
Most
circuit
theory explanations
will
be the
same
for
all
three versions. Refer to
schematic
326106
unless noted otherwise.
The Power
Supply.
The external power supply generates a regulated
5VDC
and 9VAC.
5VDC
is
applied to pins 5
and
1
of
CN7
on
the
C64
pcb. Filtered
by L5,C97, and
C100
it
is
then controlled
by
on/off
switch S1
.
This
5VDC
output
supplies the
microprocessor
logic.
9VAC
is
applied to pins
6 and 7
of
CN7
on the
C64
pcb.
+
1
2VDC, +
5VDC CAN
and
9VDC
unregulated
are outputs that are derived
from
this
9VAC
supply. The
9VAC
supply
is
made
available
on
pins
10
and
1 1
of the
USER PORT CN2.
1
2VDC
Generation
9VAC
is
rectified
by CR5.
The
unregulated
DC
output
is
filtered
by
C88
and
C89
then regulated at
1
2VDC
by
VR1
.
The
regulated
output
is
filtered
by
C57
and C59.
The
1
2VDC
supplies
the VIC and
SID
IC,
and the audio amplifiers.
C64
CIRCUIT
THEORY
VRl
+12
+S
C5S
±: :±'
C57
.22
X X
IO
-
-
Z51V
C°IO
CR5
470
INJ40OI 50V
>78I2CT
X
CRG.
IN400I
UNRE&
CAN
+5
4
CR4
M08
+5
JTcsi
^CS2
IlOO X-Z2
-
16V
-
SHIELD
GND
9
VAC
POWER INPUT
(7 -PIN MALE DIN)
CN7
+
5VDC
CAN
Generation
9VAC
is
rectified
by
CR4. The
unregulated
DC
output
is
filtered
by C19, and C95
then regulated at
5VDC
by VR2. The regulated output
is filtered
by
C102 and C103. The output
called
5VDC CAN
is
separated and individually filtered into
two
outputs
called
Vvid and
Vc. Vvid
is
the
5VDC
supply
for the video circuits,
and
Vc
is
the
5VDC
supply
for
the clock
circuits.
9VDC
Unregulated Generation.
CR6
rectifies the
9VAC
input.
The output
is
9VDC
unregulated,
and not
filtered.
This supply
powers
the cassette
motor
transistor amplifier circuits,
and the
RF modulator on
the
C64B
version.
LI
2.Z
M
H
CAN +5
IO
1.47
X
25V
-
50V
20%
CAN +5
CG5
±L
CGG
_
1.47
I
+VviD
50V
20%
LZ
+vc
10
25V
C(*7
50V
"
20%
1^7/i/n
50V
4