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7.2.2
KEYBOARD
SELF TEST
7.2.3
MONITOR CONTROL
BOARD
TROUBLESHOOTING
The
keyboard
self test
is
really
a
BURN
IN
TEST
Should
the monitor
electronic
fail,
the
follo-
This
test
sequence
will
start
running
as
soon
wing
symptoms
may be
observed:
the
keyboard
processor recognize
that
no
comu-
nication with
the
terminal
is
present. Also,
if
o
_no
picture,
regardless
of
the brightness
the keyboard
is
connected
to
a
+12V
1A
supply,
setting
then
the
self test
will
start after
a
30
sec.
-
P
delay.
The
burn
in
test
will
continue
until
o
a
very
bright
horizontal
line
in
the middle
power-off or
until
a
fault
is
detected.
The
of
the
screen
cause
to
any
detected
problem
during
this test
have
to
be
traced
further
down
to
the
component
Q
the
picture
Size
15
tg
Smal]
by
using conventional
methods.
A
faulty
key-
switch
module
is
not recognized during
this
test.
The
figure
below
shows
the contact
arm
in
nonactive
position.
With
the
key
in active
po-
sition
the
measured
resistance
across
a
contact
is
approx
100 ohm.
æl
FIG
7.2.2
KEYSWITCH
MODULE
7.2.3.1
Monitor
electronic
troubleshooting hints
The
procedure here suggested
is
to
find
the
faulty
component
by measurement
step by
step.
SYMPTOM
POSSIBLE
CAUSE
-
SECONDARY
FAULT
No
picture
ragardless
Bad V102
of
the brightness
D1
R11
and
R12
setting,
but the
C31
12V
Fuse
speaker
may
sound
and
No
e.h.t.
voltage.
the keyboard's
LEDs
works.
Bad
V3,V5,C22,C23,
C25,V105
A
very
bright
horizontal
No
+22V
to
D2
line
in
the middle
of
the
D2
R64,C22,V3.
screen.
The
tube phosphor
may
by
damaged
Vertical picture
size
to
C41
small.
No
posible to adj.
C38
by
VR9.
-
Display
Tube
reference voltages:
Measured
by
a
digital
voltmeter
and
the
Video
disconnected.
Pin
3
approx
+650V
Pin
4
approx
+125V
Pin
6
approx
-65V
Pin
7
approx
+43V
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