Tandy CM-4 User Manual

Circuits
Checked:
1.
No raster
appears.
•
Power
circuit
•
Horizontal
sync
circuit
•
Protector
circuit
2. A
high
voltage
develops
but
no
raster
appears.
•
Video
output
circuit
3.
A
high
voltage is
not
developed.
•
High voltage
circuit
NO
RASTER
APPEARS
I
Does
116V
appear
between
TP-91
and
ground?
I
No
Yes
zn
Power/horizontal
sync/protector
circuit
Check
the voltage
level
at
the
collector
of
Q851.
If
the voltage
is
normal, the
voltage
can
be varied
between
140 to
160
with the
brightness
control.
Check
the connections
between the
monitor and
computer.
Proper
CRT
and
its
related
circuits
CRT
R872
J
T602
C859
.
Yes
Defective
Does
the
signal
appear?
No
Input
circuit/
computer
Yes
UUca J.tv
d|J|Jcai
at the
emitter
of
Q402?
No
1
r
V
Input circuit/
computer
G401,G402and
its
related
Circuits
ZY77-
R413
~!
f^Q401
I
Q402
D407
i
I
D408
'
Circuits
Checked:
•
Video
circuit
and
its
related
circuits
NO
PICTURE
APPEARS
Note: If the
picture does
not
appear,
fully
rotate the
brightness
contrast control
clockwise before
inspecting.
Check the video signal
at
the base
of
Q451 with
an
oscilloscope.
Is
the
video
signal
present?
No
Yes
Yes
Check
the video
signal
at
the
base
of Q851
with
an
oscilloscope.
Is
the video
signal
present?
No
Check
Q402 and
its
related
circuits.
i
Check
the video
input
circuit
and
its
related
circuits.
Check Q451,Q851
and
its
related
circuits.
T
l
Q401
|
Q402
I
D407
r
Q451
'
Q851
1
D408
1
R850
"1
I
I
I
I
Input
cable
input
socket
computer
IC491
IC492
IC493
IC494
19

Tandy CM-4 Specifications

General

Brand	Tandy
Model	CM-4
Category	Monitor
Language	English