Commodore PLUS 4 Service Manual page 22

PLUS 4Troubleshooting
5) NO COLOR
A) Check
frequency
O.K.
B) Check
O.K.
C) Check
O.K.
D) Check
is present.
6) NO SOUND or BAD SOUND
A) Check
O.K.
B) Check
signal.
O.K.
C) Check modulator
7) SERIAL
A) Check
B) Check U7, U2 and CN2
or BAD COLOR
pin 14 for 14.31818
Ul
counter
t: 1)
If no
..
2) Check
3) Check
Ul pin 13 for Color
1) Swap
If not:
••
modulator Ml pin 55 for Color
and pin 6for
If not: 1) Check
••
CN7 pin 6to
FB4 and
1) Check
Ul pin 33 for SND signal
If not: 1) Check
•• 2) Swap
audio circuit
If not: 1)
••
Ml
1)
2) Ml pin 2to ground
3) Check
FAILURES
FB23-26 for shorts
MHz with
Check solder joints of CTI
and adjust for correct
crystal, Ql and Q2
clock circuit
opens or shorts
Out signal.
Ul w/known
Color Out signal
Ml operation
see if color
for shorts
socket for open circuit
Ul w/known
for short to ground
Check Q3 -Be sure emitter
are not shorted
pin 2for SND signal
Adjust I.F. can
modulator) for clean,
approximately 480 ohms
Ml for component
to shield
Page 33
frequency
for
good
In signal
signal
good
or loss of
and base
v.
to 55
(top right of
loud volume
should read
failure
or each other