CTX CMS-3435 User manual

| | |
RD
|
NO.
SM-0030
|
CHUNTEX
:
|
:
; | |
SERVICE MANUAL | CMS-3435/36
CAUTION:
Before
servicing
this
chassis,
it
is
important
that
the
service
technician
should
read
the
"Safety
Precautions"
and
"Product
Safety
Notice"
in
this
Service
Manual.
CONTENTS
SAFETY
PRECAUTIONG...........:::ccceeereeeteeeeees
2
DESCRIPTION
OF
CIRCUIT........0.::
cece
10
CHECK
OF
HIGH
VOLTAGE
HOLD
DOWN
ADJUSTMENTS.
...0...
cece
ecceeseeeeeeseeeeeneeeenenetes
13
CIRCUIT..........::eccsccssessrrscesnseseesesereceseeceneesensseenns
3
TROUBLE
SHOOTING...
16
PRODUCT
SAFETY
NOTICE............::ceeeeeereees
3
BASIC
CIRCUIT
DIAGRAM.............::eeeeereereee
22
FEATUREG............-cccesssssssesseseeessesnesseerereetensenenss
4
PRINTED
WIRING
BOARD...........:::csereteereees
25
SPECIFICATIONS.
.........csecccseesseseeeeeteeeeeeersenseens
5
BLOCK
DIAGRAM.
...........2.:ccceeseeseeeeeeteeeetee
eee
eetes
27
CONTROLG.......-..0.csssssssseecseseessreeneersteeesseenseneese
6
EXPLODED
VIEW
DIAGRAM.............:-
eee
28
SIGNAL
TIMING
CHART.
..........::ceeeeeeeseereeeees
8
REPLACEMENT
PARTS
LIST............-::eeeere
29
SPECIFICATIONS
AND
PARTS
ARE
SUBJECT
TO
CHANGE
FOR
IMPROVEMENT
HIGH
RESOLUTION
MULTISCAN
COLOR
MONITOR
March
1990.
EDITION
1.0

SAFETY
PRECAUTIONS
NOTICE:
Comply
with
all
cautions
and
safety
related
notes
located
on
or
inside
the
cabinet
and
on
the
chassis
or
picture
tube.
The
following
precautions
should
be
observed.
1.
Do
not
install,
remove,
or
handle
the
picture
tube
in
any
manner
unless
shatterproof
goggles
are
worn.
People
not
so
equipped
should
be
kept
away
while
picture
tubes
are
handled.
Keep
picture
tube
away
from
the
body
while
handling.
When
replacing
a
chassis
in
the
monitor,
all
the
protective
devices
must
be
put
back
in
place,
suchas
barriers,
non-metallic
knobs,
adjustment
and
compartment
shields,
and
isolation
resistor-
capacitor,
etc.
When
service
is
required,
observe
the
original
lead
dress.
Extra
precaution
should
be
taken
to
assure
Correct
lead
dress
in
the
high
voltage
circuitry
area.
Always
use
the
manufacturer’s
replacement
components.
Especially
critical
components
as
indicated
on
the
Replacement
parts
list
should
not
be
replaced
by
other
manufacturer’s.
Fur-
thermore
where
a
short
circuit
has
occurred,
replace
those
components
that
indicate
evidence
of
overheating.
Before
returning
a
serviced
monitor
to
the
cus-
tomer,
the
service
technician
must
throughly
test
the
unit
to
be
certain
that
it
is
completely
safe
to
operate
without
danger
of
electrical
shock,
and
be
sure
that
no
protective
device
built
into
the
monitor
by
the
manufacturer
has
become
defec-
tive,
or
inadvertently
defeated
during
servicing.
Therefore,
the
following
checks
should
be
per-
formed
for
continued
protection
of
the
customer
and
service
technician.
High Voltage
This
monitor
is
provided
with
a
high
voltage
hold
down
circuit
for
clearly
indicating
that
voltage
has
increased
in
excess
of
a
predetermined
value.
Comply
with
all
notes
described
in
this
Service
Manual
regarding
this
hold
down
circuit
when
servicing,
so
that
this
hold
down
circuit
may
function
correctly.
Service Warning
With
minimum
Brightness
and
Contrast
the
operating
high
voltage
in
this
display
is
lower
than
25KV.
If
any
component
having
influence
on
the
high
voltage
is
replaced,
confirm
that
the
high
voltage
with
minimum
Brightness
and
Contrast
is
lower
than
25
KV.
To
measure
high
voltage
use
a
high
impedance
high-voltage
meter.(SENSITIVE
RE-
SEARCH
Model:
ESH
or
Equivalent)
Connect
(-)
to
chassis
earth
and
(+)
to
the
CRT
anode
button.
(See
the
following
connection
diagram
Fig.
1.)
NOTE:
1)
Turn
power
switch
off
without
fail
before
making
the
connection
to
the
Anode
button.
2)
Beforeturn
power
switch
ON,
confirm
the
AC
line
voltage,
set
the
"Voltage
Selector".
CRT ANODE
HIGH IMPEDANCE
H.V.METER
SENSITIVE RESEARCH
Model:ESH
or
equivalent.
CHASSIS
GROUND
Fig. 1
X-radiation
TUBE:
The
primary
source
of
X-radiation
in
this
monitor
is
the
picture
tube.
The
tube
utilized
in
this
chassis
is
specially
constructed
to
limit
X-
radiation
emissions.
For
continued
X-radiation
protection,
the
replacement
tube
must
be
the
Same
type
as
the
original,
manufacturer
ap-
proved
type.
When
troubleshooting
and
making
test
measurements
in
a
monitor
with
a
problem
of
excessive
high
voltage,
avoid
being
unneces-
sarily
close
to
the
picture
tube
and
the
high
voltage
components.
Do
not
operate
the
chas-
sis
longer
than
is
necessary
to
locate
the
cause
of excessive voltage.

CHECK
OF
HIGH
VOLTAGE
HOLD
DOWN
CIRCUIT
Checking
of
the
high
Voltage
hold
down
circuit
operation.
1. Turn the switch of the unit OFF.
2. Set Brightness, Contrast controls to max.
3.
Connect
a
DC
Voltmeter
and
an
adjustment
jig
as
shown
in
Fig.
2.
4.
Setthe
adjustment
VR
to
fully
counterclockwise.
5.
Turn
the
switch
of
the
unit
ON
and
gradually
rotate
the
adjustment
VR
counterclockwise.
6.
Check
that
a
reading
of
DC
voltmeter
is
less
than
9.4V
+
0.5V
when
picture
disappears.
Clockwise i
Variable
resistor © TPS
To chassis
ground
VR309
500K-B H. V.
1/2
W
Protector
R391 i R390
Main Board Assembly
Fig. 2
7. Turnthe switch of the unit OFF immediately after
checking that the picture disappears.
8. Remove the adjusting jig and the DC voltmeter.
Note: Reading of 9.4V is approximately equivalent
to 28 KV of CRT Anode High Voltage.
PRODUCT SAFETY NOTICE
Many electrical and mechanical parts in the color
monitor units have special safety related charac-
teristics.
These are often not evident from visual inspection nor
can the protection afforded by them necessarily be
obtained by using replacement components rated for
higher voltage, wattage, etc. Replacement parts
which have these special safety characteristics are
identified in this Service Manual.
Electrical components having such features are iden-
tified by marking with "!" on the parts list in this Service
Manual.
The use of a substitute replacement component
which does not have the same safety characteristics
as the manufacturer recommended replacement
one, shown in the parts list in this Service Manual,
may create shock, fire, X-radiation, or other hazards.
Product Safety is continuously under review and new
instructions are issued from time to time. For the
latest information, always consult this Service
Manual.

FEATURES
OF
CMS-3435/36
Multiscan,
model
CMS-3435/36,
from
Chuntex
is
a
high
resolution
color
monitor
that
automatically
ad-
justs
to
graphics
board
scanning
frequencies
from
15.5KHz
to
38KHz.
Multiscan
gives
IBM
PC,
PC/
XT,
PC
/
AT,
PS
/
2
and
PC
compatibles
users
crisp
text
and
vivid
color
graphics
displays
when
used
with
any
of
the
IBM
graphics
adapters
(the
CGA,
EGA,
MCGA,
VGA,
or
3514A).
Multiscan
can
also
be
used
with
other
IBM
compatible
graphics
adapters
to
provide
IBM
users
with
the
widest
range
of
color
monitor
compatibility
and
capability
available
in
the
market
place.
e
CMS-3435/36
automatically
scans
all
frequen-
cies
between
15.5KHz
and
38KHz
and
is
com-
patible
with
the
IBM
PC,
PC
/
XT,
PC
/
AT,
PS
/2
and
look-alikes.
e
CMS-3435/36
uses
14
inch
fine
pitch
(0.29mm
or
0.28mm)
non-glare
CRT
and
has
a
maximum
horizontal
resolution
of
1024
dots
and
a
maxi-
mum
vertical
resolution
of
768
lines
for
superior
clarity
of
display.
e
CMS-3435/36
is
compatible
with
IBM
CGA,
EGA,
MCGA,
VGA,
8514A
graphic
adapters
and
non-
IBM
Boards
supporting
extended
display
modes
such
as
800
x
600,
132
columns
etc.
This
wide
compatibility
makes
it
possible
to
upgrade
boards
and
software
without
purchasing
a
new
monitor.
@
CMS-3435/36
offers
both
TTL
and
ANALOG
sig-
nal
inputs,
and
in
the
ANALOG
mode
can
display
an
unlimited
palette
of
colors
depending
on
the
graphics
board
and
software
being
used.
Fea-
tures
a
TEXT
SWITCH
witha
choice
of
four
colors
(red,
blue,
green,
amber)
displaying
word
processing,
spread
sheets,
data-bases
or
other
software
in
crisp
alphanumeric
text
on
a
dark-
bulb
black
background.
e
CMS-3435/36
is
equipped
with
vertical
auto
sizing
circuit.
The
circuit
works
according
to
horizontal
frequency
and
sync
polarization
of
IBM
CGA,
EGA
and
VGA
convention.
This
func-
tion
can
be
made
inactive
by
turning
off
the
Auto
Switch
located
on
front
panel
if
the
input
signal
is
non-IBM
standard.
PIN ASSIGNMENT
Glarorors
O\cooo/9
For TTL Input Signals
Pin
CGA
EGA
No.
16
colors
16
/
64
colors
1
Ground
Ground
2
Ground
Secondary
Red
3
Red
Primary
Red
4
Green
Primary
Green
5
Blue
Primary
Blue
6
Intensity
Secondary
Green
7
N.
C.
Secondary
Blue
8
H.
Sync.
H.
Sync.
9
V.
Sync.
V.
Sync.
For Analog Input Signals
D-SUB
VGA
D-SUB
9 Pin 15 Pin
1 Red 1
6 R Return 6
2 Green 2
7 G Return 7
3 Blue 3
8 - B Return 8
4 H. Sync. 13
5 V. Sync. 14
9 Ground 10
9 Ground 11
9 Ground 4
*
For
VGA
cards,
signals
are
fed
into
the
monitor
via
an
anolog
cable
which
has
9
Pin
D-SUB
connector
on
one
end
and
15
Pin
D-SUB
con-
nector
on
the
other,
and
wired
as
the
table
listed
above.

SPECIFICATION
Multiscan Monitor
Picture Tube
Pitch
Input Signal
Display Colors
Synchronization
Resolution
Video Band Width
Active Display Area
Misconvergence
Power Supply
Power Comsumption
Dimensions
Weight
Environmental
Considerations
0.29mm 0.28mm
CMS-3435 CMS-3436
13 visual diagonal inches
Dark bulb, Nonglare etching
Medium short persistance
————_—.__—__{
Video: TTL Level Positive
Analog 0.7Vp-p / 75 Ohm Positive
Sync.: Separate Sync. TTL Level
Horizontal sync. Positive / Negative
Vertical Sync. _ Positive / Negative
Composite Sync. TTL Level
Polarity Positive / Negative
Composite Sync. on Green Video
Sync. 0.3Vp-p Negative (Video 0.7Vp-p Positive)
Analog
Input:
Unlimited
colors
TTL:
8/16/64
color
Horizontal: 15.5KHz to 38KHz (Automatically)
Vertical: | 50 Hz to 90 Hz (Automatically)
Horizontal: 1024 dots Vertical: 768 lines
40MHz
(Active display area is changed by signal timing)
Preset* VGA 1024x768 EGA CGA
Horizontal: 245mm 250mm 250mm 240mm
Vertical:
185mm
187mm
190mm
180mm
*Refer To Preset Timing Chart
Less than 0.4mm
AC 120V / 60Hz or 220 / 50Hz by internal setting
75W
368(W) x 378(H) x 387(D)mm
12.8kgs
Operating Temperature o°c to 40°C
Humidity 20% to 80%
Storage Temperature -20°C to 60°C
Humidity 10% to 90%

CONTROL
il
uv fF ww NW
Power Indicator
When the power is ON, the LED is lit.
Power Switch
Used to push the power ON or OFF.
Auto Switch
When this switch is on, the VASC (vertical auto-
sizing circuit) will be activated to maintain same
picture height when changing among 350 / 400
/ 480 lines different vertical resolutions according
to the sync polarization of BM VGA convention.
For some compatible VGA boards which require
to set dip switch to support different type of mo-
nitors, their sync polarization might not be com-
patible with IBM standard if they are set to sup-
port multiscan monitor instead of standard VGA
monitor while running VGA program. In such
case, this switch should be off to make the VASC
inactive without misadjusting picture height ac-
cording to wrong polarization.
Bright Control
Used to adjust the picture brightness of the
screen.
Contrast Control
Adjusts the display to the contrast preferred by
the user.
Analog / TTL Indicator
When set in TTL mode, the LED is lit.
10.
11.
Before
connecting
MULTISCAN
series
monitor
with
IBM
personal
computers
or
compatibles
and
IBM
graphics
adapters,
take
time
to
familiarize
yourself
with
the
switches
and
controls
that
give
MULTISCAN
series
monitor
all
its
compabilities.
Manual / Auto Indicator
When set in manual mode, the LED is lit.
. TTL/ Analog Switch
Used to select an input video signal - either TTL
or ANALOG - of the graphics adapter. It is impor-
tant to determine whether the input signal of the
graphics adapter being used is ANALOG or TTL
prior to connecting the adapter with your perso-
nal computer. Refer to instructions accompany-
ing the graphics adapter for information on the
input signal.
H. Center Control
Turn this knob for the proper horizontal position
of the display. Turn the knob clockwise to repo-
sition display to the right; turn it counterclock-
wise to reposition to the left.
V. Size Control
Turn this knob for the proper vertical size of the
display. Turn the knob clockwise for a larger
display; turn it counterclockwise for a smaller
display.
V. Center Control
Turn this knob for the proper vertical position of
the display. Turn the knob clockwise for a higher
display position; turn it counterclockwise for a
lower display position.

ON AUTO ON
12
eo OFF MANUAL OFF
COLOR TEXT H-WIDTH ||
15.
12. H. Width
13.
Switch of display preferred. When this switch is
ON; the width of the display size changes.
Note: When the horizontal scanning frequency
is between 15 and 20 KHz, H. Width cannot be
adjusted.
Manual Switch
This switch selects either the IBM mode or the
manual mode. When this switch is set in Auto
mode, Multiscan automatically works in the IBM
mode and adjusts itself to the scanning frequen-
cy, resolution and color requirements of the IBM
compatible graphics adapter being used. When
this switch is set in manual mode, the user must
manually select the number of colors (8 / 16 / 64)
needed by the graphics adapter being used with
the Color Switch (see 15. below). Refer to ins-
tructions accompanying the graphics adapter
being used for information on how many colors
the adapter can display.
ud
14.
14.
15.
13. 12.
Text Switch
This switch controls the text mode of Multiscan.
When it is ON, the text of the display will appear
in one color selected by the Color Switch,
regardless of the colors of the software program
being used. When it is OFF, the color of the
software program being used will again be dis-
played. The diagram below of the dip switches
shows how to display text in your choice of four
colors. When multiscan is used with mono-
chrome cards (MDA or Hercules), please set the
Text Switch on and select one of the four colors
with the color switch (see 15 below).
Color Switch
This switch operates under following mode:
TEXT SW. OFF ON
SW.1 | SW.2 COLOR MONO
OFF ON 8 AMBER
| ON | OFF | 16 RED
| ON | OFF | 64 GREEN
OFF | OFF 64 WHITE

SIGNAL TIMING CHART
Separate Sync.
HORIZONTAL
-
VERTICAL
fo
wenn]
VIDEO
Cc
D
E
|_@
|
i
Ele
~
=
A
=
O
|
|
Sync. Polarity: Positive / Negative
Composite Sync.
Composite Sync. TTL Level
HORIZONTAL VERTICAL
l ~~VIDEO ~
2
ae
eee
el
aie
pane
ss
ee
B fe
5 a TANIA
Sync. Polarity: Positive / Negative
Equalizing Pulse is available
Composite Sync. On Green Video
HORIZONTAL ~ VERTICAL
ie oe eee |B. | ee
|
# Synd. on G: TAR UUILALAN
A —(D+B)+(5-B)
Syne. Polarity: Negative
Equalizing Puise is available
2
and 2 <= B <5uS

Display format
Horizontal Dots
Vertical Lines
Horizontal Frequency
1) Sync. Polarity
Aus
Cus
Dus
Eus
Vertical Frequency
Sync. Polarity
Oms
Pms
Q ms
Rms
Sms
PRESET TIMING CHART
EGA
8514A
31.5kHz 15.8kHz 21.8kHz 35.5kHz
31.78 31.78 31.78
1.91
25.42
0.64
70H2
14.27
0.06
1.91
11.12
1.18
25.42
0.64
70H2
14.27
0.06
1.11
12.71
0.38
25.42
0.64
60Hz
16.68
0.06
1.05
16.25
0.32
f
63
4.2
7.2
45
6.6
60Hz
16.4
0.075
1.525
12.6
2.2
45.5
4.9
1.6
39
0
60Hz
16.68
0.6
0.08
28.10
1.15
3.91
22.80
0.24
2) 87Hz
+/—
11.50
0.11
0.56
10.80
0.02
1) When AUTO SWITCH is on, the vertical auto-sizing circuit will be active according to sync.
polarity in VGA mode.
2) 8514A uses interlace mode.

DESCRIPTION OF CIRCUITS
Power Supply Circuit
The power supply consists of 2 regulators, one
is a non-synchronous self-excited power con-
verter which supplies 200V, 95V, 21V, 12V, 6V,
the control loop is to keep 95V regulated, Q103
serves as an error amplifier, |C101 (4N35 optical
coupler) couples back the error to the primary
side to control the on time of the driver Q102,
thus controls the off time of the switcher Q101,
this loop tends to regulate the 95V output, once
the 95V is reached, Q102 turns on and Q101
turns off, then the energy stored in the trans-
former transfers to the secondary side. When
the energy is dried out, an induced magnetic
force turns Q101 on, the current flows through
Q101 to the current limiter R110, a sawtooth
voltage is thus set up across R110, this voltage
couples through R109 and C110 to the base of
Q102, imposes on a DC level controlled by the
error amplifier Q103. When the 95V tends to
drop due to a heavy load, the DC voltage of Q102
base drops too, so it takes longer time for the
sawtooth imposed on this DC to reach the on-
threshold of Q102 base, the result is that Q101
will switch on for a longer time, and output more
energy to make the 95V output back to its level.
When the load is getting lighter, the 95V outputs
tends to rise, this makes the DC in Q102 base
higher, so the sawtooth takes less time to turn
Q102 on, and cut Q101 off, so Q101 will turn on
for a shorter period, the energy being transferred
is less and the 95V output is kept constant.
The multiple secondary output DC voltages are
as follows:
200V to be further regulated to supply
horizontal deflection output
stage.
95V mainly for video output amplifier
and horizontal drive circuit.
21V _ is for vertical deflection output
amplifier and frequency voltage
conversion circuit.
12V __is for deflection processing IC
and sync separation circuit.
6V _ isfor CRT heater and logic circuit
on interface board.
The 200V output is further regulated by a
synchronous step down regulator to a voltage
ranging from 50V up to 120V for the horizontal
deflection output circuit and maintains the CRT
anode voltage fairly stable in spite of various
Scanning frequencies.
10
The step down converter is synchronized with
horizontal scanning frequency. The horizontal
drive pulse is taken from IC301(LA7850), ampli-
fied by Q104, then differentiated through C122,
and the voltage sensed for comparing is taken
from the FBT secondary voltage, error amplifier
Q108 amplifies the difference between reference
voltage (ZD104 + D114’s forward voltage) and
the sensed voltage for comparing, the result is a
DC level variation in the base of Q105. The diffe-
rentiated horizontal pulse from C122 is imposed
on this DC, thus the DC level variation can deter-
mine the on / off time of Q105. Q105 will turn
Q106 on / off, and Q106 drives the output Q107
through the drive transformer. When Q107 is on,
current flows through choke L104 and charges
C128 to the desired level, when Q107 is off, the
energy stored in L104 will charge C128 through
the fly-wheel diode D112 to maintain the output
voltage. This output voltage applies to the FBT
and generates the desired H.V.. Since the sens-
ed voltage for comparing is taken from FBT se-
condary side, it is propotional to the H.V., any
variation in H.V. will reflect on the sensed volt-
age, through the control loop, the supplied DC
voltage for FBT always tends to regulate this
variation and generates a fairly stable H.V.
Video Circuit
The input signals from 9 Pin D type connector
are first selected by the TTL / Analog Switch
(SW401). If the video signals are analog RGB
signals, it will be sent directly to the video
preamplifier 1C501 (M51387P), and the signals’
level is controlled by Q403 and Q404 for users
to adjust picture contrast to their preference. If
the video signals are TTL RGB signals, before
being sent to the video preamplifier |C501, the
signals are first processed with color mapping
and mixing circuit.
TTL RGB signals are sent to 1C401(82S147)
through buffer 1C402(7407). 1C401 is a PROM
(Programmable Read Only Memory) served as
‘color mapping table for different colors combi-
nation. Pin 17 and Pin 18 of this IC are mode
control pins for selecting 8, 16, 64 colors or mo-
no text. When the Auto / Manual Switch (SW1)
located on the rear panel is set at Auto mode,
1C401 will automatically output 8, 16 or 64 colors
signals according to IBM CGA / EGA standard.
But if the input signals are from computers not
compatible with IBM PC, then SW1 should be set
at Manual mode, and 8, 16 or 64 colors can be
displayed by setting the Dip Switch (SW3) manu-
ally. When Text Switch is ON, 1C401 will output
signals to display single color, and users can
select Red, Blue, Green and Amber by setting
Dip Switch (SW3).

Each three color signal pairs are then mixed
together by Q406, Q407, Q410, Q411, Q414 and
Q415 to be RGB signals with analog values. The
level of these signals is also controlled by
Q403 for users to set contrast. Finally these
signals are output to the video preamplifier 1C501
through buffers Q408, Q412 and Q416. -
1C501(M51387) is a video processing iC
equipped with three DC amplifiers to preamplify
RGB signals from 0.6V to 2V. The voltage gain
of these amplifiers is all DC controlled, so simple
voltage divider with resistors and trimmers can
be used to adjust the voltage gain of each RGB
signal’s amplification and thus achieve a well
balanced white picture. Clamping circuit is also
included in this IC to obtain a constant black level
on the amplified video output signals.
Let us take Red signal channel for instance, and
the same principle applies on both Green and
Blue signal channels. The input signal is AC
coupled through C501 to Pin 3 of IC501, the
voltage setting on Pin 4 of IC501 determines the
voltage gain of the Red Preamplifier, this voltage
is controlled by VR501 together with R504 and
R505. VR501 is thus designated R Subcontrast
adjustment which is to be adjusted together with
the other two Subcontrast adjustments to
achieve a well balanced white picture.
Clamping pulse to Pin 15 of 1C501 is taken from
Pin 12 of 1C803(74LS123) to trigger the internal
DC Restoration circuit in order to obtain a cons-
tant black level of the Red video signal output
from Pin 29 of IC501. Now this Red signal output
is ready to drive video output stage located on
CRT board.
Voltage setting on Pin 14 of IC501 further deter-
mines the voltage gain for all three channels and
can be used as user contrast control. An ACL
(Automatic Contrast Limit) circuit is equipped in
this monitor to prevent the CRT from being over-
driven. When anode current grows larger than
the limiting threshold, the voltage on Pin 14 will
drop and decrease the gain to force the video
signal output from 1C501 smaller and the anode
current is limited within 350uA for long term ope-
ration.
The video output stage contains three identical
cascode amplifiers to amplify the video signals
from 1C501 to the level of 45Vp-p capable of
driving CRT. These large signals are AC coupled
to the CRT cathods, and the Brightness control
circuit introduces a DC voltage onto each cathod
for CRT cut-off and Brightness control.
11
3. Deflection Circuit
3.1 Sync Processing Circuit
The sync processing circuit can handle both TTL
level separate or composite sync of any polarity
and composite sync on Green Video of negative
polarity. For TTL sync, the horizontal sync is
sent to Pin 2 of IC404(74LS136), then processed
by Q421, Q423 and XOR gate of IC404 to get a
positive sync pulse on Pin 6 of IC404 in spite of
the polarity of input sync. For composite sync
on Green Video, signal is sent to peak detector
Q418, the detected sync tip is then amplified by
Q419, Q420 and shaped by XOR gate to get also
a positive sync pulse on Pin 11 of 1C404. The
monitor can not synchronize with two sync sig-
nals at the same time, so Q422 serves as a switch
to turn off the detected composite sync pulse
whenever there is a TTL horizontal sync
detected. The positive sync pulse is then
processed by Q424, Q301 and sent to Pin 1 of
1C301(LA7850) for sychronization.
For TTL separate vertical sync, it is sent to Pin
10 of 1C404 and output from Pin 8 of |C404, but
if the vertical sync is in composite form, then it is
filtered out by R469, C419, R470, C420 from the
sync pulse detected on Q424, and sent to Pin 9
of 1C404, also output from Pin 8 of IC404 to be
further processed.
3.2 Frequency Voltage Conversion Circuit
The horizontal sync pulse from Q301 is also sent
to Pin 7 of frequency voltage converter IC302
(IR9331) to be converted into a DC voltage which
is proportional to the sync frequency. This vol-
tage is compared with the reference voltage by
the comparator circuit to identify the horizontal
frequency and make necessary changes of the
parameters in the deflection circuit.
The voltage output of the horizontal frequency
voltage conversion circuit has an upper limit
about 14V set by R342, R343 and D306, also a
lower limit about 5.5V set by D307 and IC301 (OP
Amp.). These limits ensure that the monitor will
not go out of the specified scanning range and
cause any damage of the output stage.
The vertical sync pulse from Pin 8 of |C-404 is first
processed by 1C405 to obtain uniform polarity
pulse in spite of input sync polarity change. It is
then sent to both 10301 (LA7850) for sychroniza-
tion and 1C202(HA17555) for frequency voltage
conversion. The converted DC voltage is used
to determine whether input frequency is higher
than 80H, if it is, then the vertical deflection pa-
rameters are preset to conform with IBM 8514A
graphic standard which uses 87Hz for vertical
interlaced scanning frequency.

3.3 Comparator Circuit
The comparator circuit including 1C304 and its
peripherals follows the criterion listed below to
achieve necessary changes and presettings of
deflection circuit parameters. It is powered with
a precise 16V regulated from 21V to ensure the
Circuit free from fluctuations caused by power
supply. Q305 and Q306 make up the 16V regu-
lator and VR 303 can be adjusted to output exact
16V DC.
A. Horizontal Oscillation Presetting
15 — 26 26 — 38
High Low
Low High
Frequency(KHz)
IC 304 Pin4
(LM339) Pin 13
Pin 3,4
(4066) Pin 1,2
Hold (1) is first set for 26 — 38KHz range, then
set Hold (2) for 15 — 26KHz, in the latter, Hold
(1) is included in the oscillation circuit and should
not be altered when adjusting Hold (2).
Oscillator
B. Horizontal Position Presetting
Graphics | VGA | EGA | CGA | 8514A
1C304
Pin 1 Low | High | High | Low
Pin 2 Low | Low | High| Low
Pin 13 Low ; Low | Low | High
1C306
Pini0,11 Off On On Off
[_———————I3-— OT OOCO.,.e.e-:-_"|
H.
Center
|
(1)
(2)
(3)
(4)
Shorter
ee
Retrace
12
D. Horizontal Linearity Presetting
Graphics VGA | EGA CGA
IC304 Pini; Low | High High
(LM339) Pin2|} Low | Low High
Q309 Off Off On
Q310 Off On On
a
$-Curve C322 C322 C322
Capacitor Alone | //C330 | //C330
Value //C331
3.4 Horizontal Deflection Circuit
1C301(LA7850) performs the signal processing
for both the horizontal and vertical output
stages. The horizontal sync from Q301 is sent
to Pin 1 of C301, and the phase of the sync pulse
is shifted for horizontal position control. The
shifted level is controlled by Resistors connected
to Pin 2, and the duty of the shifted sync pulse is
determined by R308 connected to Pin 3.
Flyback pulse comes to Pin 4 and a sawtooth
waveform is generated to be compared with the
phase of the shifted sync pulse by the AFC
(Automatic Frequency Control) circuit of 1C301.
Control voltage determined by the AFC ciucuit is
output from Pin 7, then fed into Pin 8 through
R310, Pin 8 is the input pin of VCO (Voltage
Control Oscillator), and locks the VCO to be
sychronous with the input sync pulse.
The synchronized VCO output is further shaped
for driving the output stage, drive signal is output
from Pin 12. Voltage setting on Pin 11 deter-
mines the duty cycle of the drive pulse. Pin 13
is the input of the X-Ray protector, once the
Anode voltage is higher than the set threshold,
the sensed voltage will trigger Pin 13 and turn the
SCR on to shut down the drive signal, the
horizontal deflection output stage is thus turned
off to avoid excessive radiation from CRT.
The drive pulse from Pin 12 is sent to transistor
Q302, through T301, drives the horizontal output
transistor Q303 on and off. When Q303 is turned
on, current flows through horizontal deflection
coil and the primary winding of the flyback trans-
former stores energy. When Q303 is turned off,
B+ charges C322 through deflection coil, cur-
rent flows in opposite direction, and the energy
stored in FBT couples to the secondary side,
supplys Anode voltage and the secondary load.
A H-Width coil connected to deflection coil can
be adjusted for suitable width.

ADJUSTMENTS
3.5 Vertical Deflection Circuit Monitor adjustments contained in this section
should be followed whenever a major component is
replaced, such as a CRT / YOKE assembly ora circuit
board. Some adjustments may also be required pe-
riodically to correct for component aging. Adjust-
ments should be performed in specific order given in
The vertical sync pulse from Pin 6 of IC 405 is
sent to Pin 19 of IC301(LA7850) to trigger the
vertical oscillator to be synchronous with the
input sync. The synchronized vertical sawtooth
signal is then taken from Pin 16 to Pin 2 of vertical
output amplifier 1C201 (LM7837). 1C201 con- the following paragraphs.
tains its own driver functions, so the AC / DC 1. Power Supply Circuit
feedback loop can be implemented on this (1) VR101 +95V Adjustment
single IC, problems with crosstalk from the (2) VR102 Def. B+ Limit Adjustment
horizontal signal affecting interlace charac- (3) VR103. +6V Adjustment
teristic is reduced. The DC feedback is sent to
Pin 7 through VR206, R243 and VR203, AC feed- 2. Horizontal Deflection Circuit
back is also sent to Pin 7 through VR205, R243. (1) VR301 H-Center Adjustment 1
Adjusting VR205 and VR 206 can achieve best (2) VR302 ~H-Hold Adjustment 1
linearity, VR203 determines the DC bias point of (3) VR303 +16V Adjustment
the output amplifier. Voltage setting on Pin 4 will (4) VR304 Horizontal Frequency Voltage
determine the sawtooth peak level of the Ramp Conversion Adjustment
generator circuit, thus can be used to adjust for (5) VR305 ~~ H-Center Adjustment 3
vertical size control. Q201, Q214 — Q219 and (6) VR3806 ~H-Center Adjustment 2
their peripherals serves as vertical auto sizing (7) VR307 ~—_H-Hold Adjustment 2
circuit to maintain same vertical size when (8) VR308 —H-Center User Control
changing among 350 / 400 / 480 lines resolutions (9) VR309 X-Ray Protector
according to IBM VGA conventions. VR201 is (10) VR310 High Voltage Adjustment
user vertical size control and VR202 determines (11) VR311. H-Center Adjustment 4
the suitable contro! range for VR201. (12) L305 H-Width Adjustment
4. CRT Bias Circuit 3. Vertical Deflection Circuit
The DC bias voltages for R, G, B CRT cathods (13) VR201 —-V-Size User Control
are supplied by Q213, Q206 and Q207. Q208, (14) VR202 \V-Subheight Adjustment
Q209 and Q210 control the DC level of each gun (15) VR203 V-Bias Adjustment
by adjusting VR211, VR212 and VR213. Q212is (16) VR204 Side-Pin Adjustment 1
for brightness control, it solely controls the DC (17) VR205 = ~‘V-Linear Adjustment 1
levels of all three guns. VR214, VR215 and (18) VR206 V-Linear Adjustment 2
VR216 are sub-bright controls to achieve precise (19) VR207 Side-Pin Adjustment 2
gray background over the entire range of bright- (20) VR208 ‘Vertical Frequency Voltage
ness control. Conversion Adjustment
(21) VR218 V-Hold Adjustment
4. Video Circuit
(22) VR211 R Bias Adjustment
(23) VR212 G Bias Adjustment
(24) VR213 __B Bias Adjustment
(25) VR214 —-R Subbright Adjustment
(26) VR215 GSubbright Adjustment
(27) VR216 ~—_B Subbright Adjustment
(28) VR401 User contrast control
(29) VR501 R Subcontrast Adjustment
(30) VR502 G Subcontrast Adjustment
(31) VR503. ~—B Subcontrast Adjustment
(32) VR504 Subcontrast
For quick reference, page 21 shows the locations
of all adjustments.
13

When
adjusting
the
monitor,
receive
a
full
screen
white
pattern
set
at 20
ft-L
unless
otherwise
speci-
fied.
1. Power Supply Voltage Check
When the monitor is working normally, the vol-
tages at plug P301 on main board are as follows:
v1
V2
V3
95V+ 0.5V for video o/p AMP
Ground
21V+ 0.5V for vertical o/p AMP
Voltages at P405 on interface board are as fol-
lows:
B1
B2
B3
(1)
(2)
(3)
(4)
12V 0.5V for deflection IC & video preamp
Ground
6V+ 0.1V for heater and logic circuits
Receive VGA 400 lines Signal with full
white pattern.
Adjust VR101 to obtain 95V+0.5V.
Adjust VR102 to Mechanical center position.
Adjust VR103 to obtain 6V+0.1V.
2. Sync and Deflection Circuit
2.1
(1)
(2)
(3)
2.2
(1)
(2)
(3)
(4)
(6)
(6)
Horizontal Frequency Conversion Circuit
Receive VGA (400 lines) Signal with full
screen white pattern.
Adjust VR303 to obtain 16V+0.2V on TP1.
Adjust VR304 to obtain 12.2V+0.1V on TP6.
Horizontal Oscillation
Receive VGA (400 lines) Signal with cross
hatch pattern.
Bypass the sync signal by connecting a 10u
/25V capacitor to TP2 and ground, capacitor
positive side is on TP2.
Adjust VR302 to make the picture stand still
or move slowly toward left or right.
Receive CGA signal with cross hatch pattern.
Adjust VR307 to make the picture stand still
or move slowly toward left or right.
Disconnect 10u/25V capacitor, check mon-
itor picture be steady when receiving display
modes range from standard VGA up to
8514A, if not, repeat procedures (1) through
(5) more carefully.
2.3 Vertical Oscillation
(1)
(2)
(3)
(4)
Receive VGA (400 lines) signal with cross
hatch pattern.
Adjust VR208 to obtain 7.8V+0.2V on TP8.
Disconnect VGA input signal.
Adjust VR218 to obtain 50Hz+1Hz vertical
free-run oscillation. Use counter or scope to
measure frequency on the positive side of
the vertical deflection coil, which is easily
accessed on one of the yoke assembly con-
tact points.
14
2.4 High Voltage Circuit
(1)
(2)
(3)
(4)
Receive VGA (400 lines) signal with full
screen.
Adjust contrast and bright controls to mini-
mum intensity.
Adjust VR310 to obtain 31.4V+0.2V on TP7.
This
reading
is
approximately
equivalent
to
24KV of CRT Anode High Voltage.
In some extreme cases, TP7 may not reach
31.4V
when
adjusting
VR310.
It’s
because
the
VR102
adjustment
limits
the
DC
voltage
supply to FBT, so put the VR310 in mecha-
nical center position, then adjust VR102 for
TP7 to be 31.4V+0.2V.
Adjust VR309 to obtain 8.2V+0.1V on TP9,
this will set the X-ray protector to hold
down the horizontal deflection output when
the Anode High Voltage exceeds 29KV.
2.5 Horizontal Center
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
Receive VGA (400 lines) signal with full
screen white pattern.
Adjust VR301 to ensure that the external
H.
Center
control
VR308
has
a
symmetric
range
to
shift
the
picture
toward
left
and
right
then
adjust
VR308
to
put
the
picture
in the center of the screen.
Receive EGA signal with full screen white
pattern.
Adjust VR306 to put the picture in the center
of the screen.
Receive CGA signal with full screen white
pattern.
Adjust VR305 to put the picture in the center
of the screen.
Receive 1024X768 signal with full screen
white pattern.
Adjust VR311 to put the picture in the center
of the screen.
2.6 Vertical Linearity
(1)
(2)
(3)
(4)
Receive VGA (400 lines) signal with cross
hatch pattern.
Adjust V. BIAS VR203 to the mechanical
center position.
Adjust VR206 so the top blocks are equal
to the bottom blocks.
Adjust VR205, so the center blocks are
equal to the top and bottom blocks.
2.7 Vertical Size
(1)
(2)
(3)
Receive 1024X768 signal with cross hatch
pattern.
Adjust the external user control VR201 clock-
wise
to
obtain
maximum
vertical
size.
Adjust VR202 to obtain full screen picture
height.

(4) Observe the picture to see if there is any fold
over on top or compression at the bottom of
the picture, adjust VR204 to obtain a normal
picture.
Readjust VR201 to obtained 187mm + 2mm
picture height.
(6) Receive CGA signal with cross hatch
pattern.
) Check picture height be 180mm + 3mm.
(8) Receive one of VGA signals (3850/400/480
lines).
(9) Turn the Auto Switch on the front panel to
ON position.
(10) Check picture height be the same 185mm
+3mm when changing among the 350/400
/480 lines different vertical resolution display
modes.
G
2.8 Side Pincushion Correction
(1) Receive EGA signal with cross hatch
pattern.
(2) Adjust VR204 for best side Pincushion
correction.
(3) Receive VGA 400 lines and 480 lines signals
and check side pincushion correction, fine
tune VR204 if necessary to obtain best
correction.
(4) Receive 1024X768 signal with cross hatch
pattern.
(5) Adjust VR207 to obtain best side Pincushion
Correction.
2-9 Horizontal Size
(1) Receive VGA (400 lines) signal with cross
hatch pattern.
(2) Adjust L305 to obtain 250mm + 2mm
picture width.
3. Video Circuit
Prior to the video circuit adjustment, all sync and
deflection circuit adjustments must be completed,
the monitor must have been warmed up for more
than 30 minutes.
Video signal must have 75Q impedance and cor-
rect voltage at the monitor input terminal. Before
adjusting, make sure VR501, 502, 503, 214, 215,
216, 211, 212, and VR213 are preset to the me-
chanical center position.
3.1 Cut Off Adjustment
(1) Receive VGA (400 lines) signal with a blank
pattern (black).
(2) Turn the screen VR on the FBT counterclo-
ckwise to minimum, then turn it clockwise
until the background raster is just visible on
the screen.
(3) Adjust VR408 and VR410 to obtain a gray
blackground raster.
(4) Turn the screen VR counterclockwise to
the position that the blackground raster is
just diminished.
3.2 White Balance Adjustment
(1) Receive VGA (400 lines) signal with full
screen white pattern.
(2) Set user contrast control to its minimum
and bright control to its maximum.
(3) Adjust VR214, VR215, VR216 to read CIE
coordinate X= 0.281+ 0.015, Y= 0.311+
0.015 using Minolta Color Analyzer II.
(4) Set user contrast control and bright control
to their maximum.
(5) Adjust VR501, VR503 to read the same CIE
coordinate as step (3).
(6) Set user contrast control to its maximum
and bright control to its minimum.
(7) Check CIE coordinate be within + 0.015
limits, if not, fine tune VR214, VR215, VR216
for compensation.
(8) Adjust user contrast control to 20 ft-L and
check for CIE color coordinate, if it is not
right, go back to step (4).
3.3 Brightness Adjustment
(1) White balance must have been adjusted
prior to this adjustment.
(2) Receive VGA (400 lines) signal with stair
step pattern.
(3) Set user contrast and bright control at their
maximum.
(4) Adjust screen VR on FBT so that the first
step of the stair step signal can just be
seen.
(5) Receive same signal with 60 X 60mm white
pattern.
(6) Check brightness be within 55 ft-L through
70 ft-L.
4. Focus Adjustment
(1) Receive VGA (400 lines) signal.
(2) Set user contrast and bright control at their
maximum.
(3) Adjust focus control on the FBT so that
focus at the middle points between the cen-
ter of the screen and the four corners to its
best. This is to make the focus for the full
screen area even.

TROUBLE SHOOTING
Should
trouble
shooting
be
required,
the
service
routines
are
provided
on
the
following
pages
to
facilitate
location
of
a
fault.
In
addition,
materials
listed
below
may
be
helpful
while
trouble
shooting.
(1) Description of Circuit
(2) Basic circuit diagram
(3) Block diagram
16

YES
YES,
PICTURE
DIAGNOSIS
DEFLECTION] YES
PROBLEM
VIDEO
PROBLEM
BRIGHTNESS | YES
PROBLEM
SIGNAL
PROBLEM
ADJUST SCREEN VR
RASTER OR PICTURE ?
POWER BOARD
SERVICE ROUTINE
ADJUST SCREEN VR
RASTER OR PICTURE
MAIN SERVICE ROUTINE
START
| NO
CHECK POWER BOARD |OK
G O/P 95V/21V/12V/6V
SERVICE ROUTINE
| CHECK DEF.B +
50V ~ 120V
AULT | Fix OR REPLACE
IF
[FO
DEFLECTION BOARD |FAULT
BAD COMPONENTS
IS H. V.
PRESENT ?
CRT BOARD
SERVICE ROUTINE
BIAS & BRIGHTNESS | RALLE
SERVICE ROUTINE (FOUND
INTERFACE BOARD |FAULT
SERVICE ROUTINE
|
FAULT |
FOUND" FIX OR REPLACE
| BAD COMPONENTS:
J
|
| FIX OR REPLACE
BAD COMPONENTS
FIX OR REPLACE :
BAD COMPONENTS
FIX OR 5s ——
FOUND | BAD COMPONENTS
PROBLEM |NO
SOLVED
FINISH |
17

A. POWER BOARD SERVICE ROUTINE
POWER INDICATOR LED OFF
POWER CORD
NO
OK
R101,
7101
DOES
AC
APPEAR
ON
BD101
|
AC
FILTER
POWER SW.
FAILURE
BD101, C101 ~ C104
C105 ~ 107, R102, 103, Q101, Q102
DOES DC 320V APPEAR
ON BD101 +/- PIN
DRIVER PART & FEEDBACK LOOP
COMPONENTS !C101 (PHOTO COUPLER)
VR101, R110
CHECK G O/P
95V/21V/12V/6V
CHECK RESPECTIVE LOAD
CHECK 200V ON
C118
CIRCUIT
OF
EACH
VOLTAGE
D108, C118, Q107
C128
Q107, Q106, C128, Q124, Q105
Q108, ZD104, SYNC ON F2
FEEDBACK ON D2, R131,127
R133, R140,L104,C131
CHECK CONNECTOR D
D1 FOR 50V ~ 120V
CHECK HORIZONTAL
DEFLECTION CKT
OK
18

B. DEFLECTION BOARD SERVICE ROUTINE
H-SYNC ON TP 2 NO Q301, GO TO INTERFACE
V-SYNG ON C221 -——————-| __ BOARD SERVICE ROUTINE
emreerane
YES
21V, 16V, 1C302 AND
CHECK F/V O/P
PERIPHERAL CKT COMPONENTS
VOLTAGE TP 6
COMPARATOR
NO
10303,
1C304
&
VOLTAGE
LOGIC O/P
DIVIDER RESISTORS
YES
1C301, X - RAY PROTECTOR,
1C305, 1C306, VR301 ~VR307,
RC COMPONENTS AROUND !C301
H - OSCILLATOR
& H - CENTER
>>>
1C301, X - RAY PROTECTOR,
Q302, Q303, D301, FBT,
C313 ~ C315, C330 ~C331,
C332, Q307, 309, 308, 310
1C301, 1C201, IC202
Q201, VR201~205
& PERIPHERAL COMPONENTS
H - DRIVE
H - O/P & H. V.
YES
VERTICAL
DEFLECTION
SIZE, LINEAR
Q204, Q205, VR204, Q221,VR207,T302
SIDE PIN
Q202, Q203, R213
V. CENTER
19