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TROUBLESHOOTING
(Continued)
No
5.0V
at
pin
9
of
Connector
SK3-1.
Check
the winding on Transformer
T1
from pin
11
to
pin
13
for
continuity
and
check
Diode
D9,
Capacitors C19 thru C22 and
Coil L2.
MICROPROCESSOR
(CPU)
OPERATION
Microprocessor
IC
(U36)
not
working.
Check
for
a
7.159MHz waveform at pin
19
of
IC
U36.
If
the
waveform
Is
missing,
refer
to
the
"Oscillators
and
Dividers"
section
of
this
Troubleshooting
guide.
If
the waveform checks
good,
check the
logic
reading at pin
21
(Re-
set)
of
IC
U36 while turning the Computer
On.
The
reading
should be High
when the Computer
is
turned
On,
then
go Low.
If
the reading
is
not
correct, check the
logic
reading at pin
21
of
IC
U51
while turning the Computer
On.
The
reading
should
be
High
when
the
Computer
Is
turned
On,
then
go Low.
If
the reading
is
not
correct,
check Capacitors C134
and C135,
Diode
CR2,
Reset Switch
SI
and Resistor R38.
If
the
reading
is
correct
at pin
21
of
IC
U51,
check
IC
U51.
OSCILLATORS AND DIVIDERS
Verify Oscillator Modules
(Y1
and
Y2)
are work-
ing
properly
by
checking for
a
28.636MHz sig-
nal
at pin
27
and 16.0MHz signal
at pin
14
of
IC
U51.
If
the
28.636MHz
signal
is
missing or
frequency
is
not
correct,
check
Oscll lator
Module
Y1
.
If
the
16.0MHz
signal
is
missing
or
frequency
is
not correct,
check Oscll
lator
Module
Y2.
If
the
Oscillator
Modules
check
good,
check
the
dividers
In
IC
U51
by
checking
for
a
1.193MHz
signal
at pin
3,
8.0MHz
signal
at pin
11,
14.318MHz signal
at pin
12,
3.
5795MHz sig-
nal
at
pin
13,
7.16MHz
(4.77MHz
in
normal
speed mode) signal
at pin
16,
500KHz signal at
pin 38 and
4.0MHz signal
at pin 39
of
IC U51
If
any
of
the signals are not correct,
check
IC
U51.
KEYBOARD
Keyboard
does
not
function.
Check
Keyboard
Connector
J4
on
the System Board and Connector
CN
on
the
Keyboard
for
good
connections
and
check
the Keyboard Cable
for
broken wires.
If
the Connectors
and
cable check
good,
check the
waveforms
at
pins
1
and
4 of
Connector
J4
on
the System Board while pressing the Space Bar
on
the Keyboard.
If
the waveforms check
good,
check
IC
U22 on the
System Board.
If
the wave-
forms
are missing,
check the waveforms at pins
2,
21
thru 24
and
27
thru 34
of
Keyboard Con-
trol
I
er
IC
(Ml)
on
the Keyboard.
If
the wave-
form
Is
missing
at
pin
22,
check
the
6.0MHz
Crystal
(XL)
and
IC
Ml.
If
any
of
the other
waveforms
are
missing,
check
IC
Ml.
If
the
waveforms
check
good,
check
for
pulses at pins
37
and
38 of
IC
Ml
while pressing
a
key.
If
pulses
are
missing,
check
IC
Ml.
If
pulses
are present, check
IC
M2.
No
Sound.
If
there
Is
no
sound
from
the
Internal
speaker,
check
the
setting
of
the
Volume Control
(R26A).
The
Control
should
be
set
to
Maximum clockwise
for
Maximum
volume.
If
the
Control
is
set
properly,
type
In
and
run
the following Basic
program:
10
PRINT CHRS(7): GOTO
10
The
program
produces
a
continuous
audio
tone
of
about 1100 Hertz.
While the program
is
run-
ning,
check
for
pulses
at
pin
13
of
IC
U19.
If
pulses
are
missing,
check
IC
U19.
If
pulses are present,
check
for
pulses
at
pin
6
of
IC
U20.
If
pulses
are
missing,
check
IC
U20.
If
pulses are present,
check
for
pulses
at pin
13
of
IC
U51
.
If
pulses are missing,
check
IC
U51.
If
pulses
are
present,
check
for the
waveform shown
In
Figure A at
pin
7
of
IC
U37A.
If
the waveform
is
missing, check
IC
U37A.
If
the waveform
Is
present, check for
a
logic High
at
pins
26
and
27 and
logic Low at
pin
28 of
IC
U22.
If
any of the
readings are
not
correct,
check
IC
U22.
If
the
readings
are correct,
check
for
a
logic
High at pin
2
of
IC
U47.
If
the
reading
Is
not
correct,
check
IC
U47.
If
the
reading
Is
correct,
check
for
the
waveform shown
In
Figure A at
pins
9
and
10 of
IC
U25.
If
the
waveform
Is
missing
4V
REF
Figure A
at
either
pin,
check
IC
U25.
If
the waveform
is
good
at
IC
U25,
check
for
the
waveform
shown
In
Figure
B at pin
1
of
IC
U26.
If
the
waveform
Is
missing,
check
the
voltages
and
components
associated
with
IC
U26.
If
the
waveform
checks
good,
check
for
the
waveform
shown
in
Figure
C
at
pin
5
of
IC
U27
(with
Volume
Control
R26A
set
at
Maximum
volume).
If
the waveform
Is
missing, check the voltages
and
components associated with
IC
U27.
If
the
waveform
checks
good,
check
Capacitor
CI
30,
Connector
J1
and
Speaker
SP1
r
r r
•
4V
5mSec
•
2V
REF
Figure B
NORMAL/TURBO
CPU
CLOCK
Figure C
2V
.
5mSec
2V
REF
To
check
the
CPU
clock
switching
circuits,
type
In
and run the
following program:
10
OUT 98,32: PRINT "NORMAL (4.77MHz)
H
20
AS=lhKEYS:
IF
AS=
H
"
THEN 20
30 OUT 98,40:
PRINT "TURBO (7.16MHz)"
40
AS=INKEYS:
IF
AS="" THEN 40 ELSE
10
16
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