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PRELIMINARY SERVICE
CHECKS
(Continued)
SERVICE
CHECKS
MATCH
THE
NUMBERS ON
THE INTERCONNECTING DIAGRAM
AND PHOTOS
WITH
THE
NUMBERS ON
THE
SERVICE
CHECKS
TO
BE
PERFORMED.
©
©
©
COMPUTER DEAD
(A)
Check
for
5.0V
at pin
1,
-12.0V
at
pin
8
and 12.0V at pin
9
of
Connec-
tor
J6
on the System Board.
If
the
voltages
are
correct,
go
to
part
(D).
If
the
voltages
are
not
cor-
rect,
check
the
adjustment
of
the
5V
Adjust
(VR1)
and
12.0V
Adjust
(VR2)
Controls
on
the
Power Supply
Board,
see
"Mi seel
laneous
Adjust-
ments."
(B)
If
the voltages are missing at Con-
nector
J6,
turn
the
Computer
Off
and
disconnect the power connectors
from
the
System
Board
and
Disk
Drive.
Connect
a
#1129
lamp
to the
5.0V
Source
(pin
1
of
Connector
J6)
and
a
#93
lamp
to the
12.0V
Source
(Pin
9
of
Connector
J6).
WARNING:
Operating
the
Power
Supply
without
a
load
may
damage
it.
Turn
the
Power
Supply
On
and
recheck
the
voltages.
If
the
voltages
are
still
missing, check Fuse
F1
(C)
If
the correct voltages return,
re-
connect
the
Power
Supply
to
the
System Board and Disk Drives one at
a
time
until
the
Board
or
Drive
that
is
causing the Power Supply to
shutdown
is
found.
WARNING:
Be
sure
Power
supply
is
turned
Off
when
connecting
to the
System Board
or Disk
Drive.
(D)
Check
the
CPU
IC
(U36)
and
ROM
IC
(U41) by
substitution.
SYSTEM BOARD
(A)
A
program
runs
for
a
while,
then
suddenly
stops
or
becomes
erratic
in
operation.
Check RAM
IC
Banks
and
1
(IC's
U1
thru U16).
KEYBOARD
(A)
Keyboard
dead.
Check Connector
J4
on
the System Board
for
good connec-
tions.
(B)
Check
the
Keyboard
cable
and
check
Connector
CN
on
the
Keyboard
for
good
connections.
(C)
Check
IC
U22 on
the System Board
by
substitution.
VIDEO
(A)
No
video.
Check
Connectors
J9
and
J10A
for
good connections and check
the
Video
cable
going
to
the
Mon-
itor.
©
©
©
(B)
(C)
Check
Video
tion.
IC
(U30)
by
substltu-
Video
display
is
not
correct.
Check
Video
IC
(U30)
and
Video RAM
IC's (U24, U31,
U34
and U35).
SOUND
(A)
No
sound
from
the
Internal
Speaker
(SP1)
and
no
audio
at
Connector
J10B.
Check
IC
U37A
by
substitu-
tion.
(B)
No
sound
from
the
Internal
Speaker
(SP1).
Check
the
setting
of
the
Volume Control
(R26A)
on the System
Board.
(C)
If
Volume Control
is
set properly,
check
Connector
J1
on
System Board
for
good
connections
and
check
Speaker
(SP1)
voice
coil
for
conti-
nuity.
DISK DRIVE
(A)
Disk
Drive
operation
Is
erratic.
Clean
the
Drive
heads.
Check
the
Drive
Spindle
Speed,
see
"Spindle
Speed Check".
(B)
Check Connectors
J1,
J2,
J4
thru
J7
and
J9
on
the Disk Drive and Connec-
tor
J5
on the System Board
for good
connections.
(C)
Drive
dead.
Check
for
12V
at pin
1
and
5V
at pin
4
of
Connector
J2
on
the
Drive
Board.
If
the
voltages
are
missing,
check
the
Power
Sup-
ply.
CD)
If
the
voltages are present at Con-
nector
J2,
check
the
setting
of
Switch
S2-3
on
the
System
Board.
It
should
be set On.
(E)
If
Switch
S2-3
is
set
On,
check
IC's
U22
and
U37
on
the
System
Board
by
substitution.
PARALLEL PORT
(A)
Paral
lei
Port
does
not
work,
check
Connector
J7
for
good connections.
(B)
Check
IC
U55
by
substitution.
IV
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