MECHANICAL PARTS LIST................................................................................................. 41
Before servicing this chassis, it is important that the service personnel must read the
“Safety Precautions” and “Product Safety Notice” in this Service Manual.
ATTACHMENT A ................................................................................................................. 45
SPECIFICATIONS AND PARTS ARE SUBJECT TO CHANGE FOR IMPROVEMENT.
HIGH RESOLUTION COLOR DISPLAY MONITOR
(Sept. 2000)
FEATURES
1. Flat screen CRT with anti-glare, dynamic focus circuit,
dark glass, and INVAR shadow mask give the
sharpest focus and highest contrast.
2. Automatic scanning and automatic adjustment to
conform to a wide range of scanning frequencies and
user requirements.
3. Signal input allows D-Sub Mini 15-pin cable.
4. Power Save Mode automatically puts the monitor into
a standby mode (power consumption less than 15W)
when the H.sync. signal is not detected, and a power off mode (less than 5W) when the V.sync. signal is not
detected. Normal mode is restored immediately when
the H. sync. signal and the V.sync. signal are detected.
This feature prolongs monitor life and reduces energy
consumption by up to about 75 %.
SAFETY PRECAUTIONS
NOTICE:
notes located on or inside the cabinet and on the chassis
or picture tube.
The following precautions must be observed.
1. Do not install, remove, or handle the picture tube in
2. When replacing a chassis in the monitor, all the
3. When service is required, observe the original lead
4 Always use the manufacturer’s replacement components.
5. Before returning a serviced monitor to the customer,
6. In the case of the microprocessor unit, shop
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 notes described in this Service Manual
regarding this hold down circuit when servicing, so that
this hold down circuit may function correctly.
Comply with all cautions and safety related
any manner unless shatterproof goggles are worn.
People not so equipped should be kept away while
picture tubes are handled.
protective devices must be put back in place, such as,
barriers, non-metallic knobs, adjustment and compartment
shields, and isolation resistor-capacitor, etc.
dress. Extra precaution should be taken to assure
correct lead dress in the high voltage circuitry area.
Especially critical components as indicated on the
circuit diagram should not be replaced by other
manufacturer’s one. Furthermore where a short circuit
has occurred, replace those components that
indicate evidence of overheating.
the service personnel must thoroughly test 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 defective, or inadvertently
defeated during servicing.
Therefore, the following checks should be performed
for continued protection of the customer and service
technician.
adjustment is necessary after exchange of the
microprocessor unit.
Service Warning
With minimum Brightness and Contrast the operating
high voltage in this display is lower than 30 kV.
If any component having influence on the high voltage is
replaced, confirm that the high voltage with minimum
Brightness and Contrast is lower than 30 kV.
To measure high voltage use a high impedance
high-voltage meter. (SENSITIVE RESEARCH Model:
ESH or Equivalent)
Connect (-) to chassis earth and (+) to the CDT anode
button. (See the following connection diagram Fig. 1.)
NOTE:
Turn power switch off without fail before making
the connection to the Anode button
CDT ANODE
HIGH IMPEDANCE
H.V. METER
SENSITIVE RESEARCH
Model: ESH or equivalent. CHASSIS GROUND
(+)
(-)
FIG. 1
X-radiation
TUBE:
The 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
approved type.
When troubleshooting and making test measurements in
a monitor with a problem of excessive high voltage, avoid
being unnecessarily close to the picture tube and the high
voltage components.
Do not operate the chassis 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 ON, and set the Brightness
and Contrast controls to max.
2. Turn the switch of the unit OFF.
3. Connect a DC Voltmeter and an adjustment jig as
shown in Fig. 2.
4. Set the adjustment VR to fully counterclockwise.
5. Turn the switch of the unit ON and gradually rotate the
adjustment VR clockwise.
6. Check that a reading of DC voltage-meter is less-than
0.60.1 V when picture disappears.
7. Turn the switch of the unit OFF immediately after
checking that the picture disappears.
8. Remove the adjusting jig and the DC voltmeter.
NOTE:
Reading of 0.6 V is approximately equivalent to
30 kV of CDT Anode High Voltage.
2
PRODUCT SAFETY NOTICE
Many electrical mechanical parts in the color monitor
units have special safety related characteristics.
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 identified
by marking with on the schematics and 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.
Productions are issued from time to time. For the latest
information, always consult this Service Manual.
SPECIFICATIONS
DC VOLT METER
(10 V range)
VARIABLE
V
Clockwise
RESISTER
To
CHASSIS
GROUND
R793
R792
DEF BOARD ASSEMBLY
FIG. 2 CHECKING CIRCUIT USING JIG
RESISTER
300 k -B (1/2 W)
68 k (1/2W)
Model Name
CM771U CM771ET CM772U CM772ET
Destination North America Europe North America Europe
Rated Voltage AC 100-120 / 200-240 V, Automatically select.
6 Vertical Frequency 70.086 Hz 85.061 Hz 84.997Hz 85.024 Hz
Front
porch
Sync.
width
Back
porch
Blanking
width
Display
time
H. period
(1H)
7 Scan System (Non-interlaced) (Non-interlaced) (Non-interlaced) (Non-interlaced)
8 Signal name 30B 54A 68A 91A
* VGA is a registered trademark of International Business Machined Corporation.
* VESA is a trademark of a nonprofit organization, Video Electronics Standard Association.
0.011 ms (1H) 0.009 ms (1H) 0.381 ms (10H) 3.548 ms (110H)
0.032 ms (3H) 0.028 ms (3H) 0.064 ms (2H) 0.129 ms (4H)
0.491 ms (46H) 0.433 ms (46H) 1.049 ms (33H) 3.097 ms (96H)
0.533 ms (50H) 0.471 ms (50H) 1.430 ms (45H) 6.774 ms (210H)
12.800 ms (1200H) 11.294 ms (1200H) 15.253 ms (480H) 13.226 ms (410H)
13.333 ms (1250H) 13.333 ms (1250H) 16.683 ms (525H) 20.000 ms (620H)
VESA
16001200
(75Hz)
9
9
(Pos./Pos.)
1600 dots1200
lines
VESA
16001200
(85Hz)
-
-
9
9
TTL Level
(Pos./Pos.)
1600 dots1200
lines
VGA
640480
(60Hz)
TTL Level
(Neg./Neg.)
640 dots480 lines 640 dots410 lines
TTL Level (Neg./Neg.)
Adjustment
signal
6
DESCRIPTION OF CIRCUIT
1. Power Supply Circuit
This model incorporates a wide range universal power supply utilizing a switching regulator (see block diagram in Fig.6).
1.1 AC input
AC input consists of AC inlet, EMI filter (C901C905,C907) and rectifier (D901D904). Rectifier circuits adapt to
full-wave method. Inrush current limiting circuit (R90A) protects from excessive inrush current at initial stage of power
on.
1.2 Switching Regulator circuit
Switching Regulator circuit is designed to handle variations of two conditions to ensure constant +B voltage to
secondary circuit : (Circuit #2) varying load conditions of video, (Circuit #3) varying horizontal frequencies and load
conditions.
1.2.1 Circuit #1 :
Circuit #1 consists of chopper inductor (L910), chopper component (Q910), rectifier component (D910, C920) and
control IC (I920). R918 and R919, R91A detect output voltage and provide signal to I920 pin 20 which adjusts the pulse
width based on the pin 20 voltage level to provide constant voltage output.
1.2.2 Circuit #2 :
Circuit #2 consists of chopper transformer (T921), chopper component (Q920) and control IC (I920). T921 detects
output voltage and provides signal to I920 pin 4 which adjusts the pulse width based on the pin 4 voltage level to provide
constant voltage output. If the secondary circuit becomes overloaded, primary current through T921 is detected at R923,
R924 and stops the switching operation. Once the circuit has overloaded, the power switch must be turned off for a
short period and then turned on to re-establish power.
Switching frequency is determined by time constant of R92E and R92F, R92G.
1.2.3 Circuit #3 :
Circuit #3 has two outputs. +5V is used mainly to drive the microprocessor circuit and input the signal selection circuit.
+6.3V is used for the CRT heater.
When the DC voltage from circuit #1 is applied to I940, I940 starts oscillations. Once oscillations start, the switching
transistor is driven by the voltage taken from the tertiary winding of T940. The output voltage of the T940’s tertiary
winding is rectified by D942 and C942.
The main power supply (Circuit #2) turns on (off) when a signal High (Low) is applied to the base of Q984 from the
microprocessor circuit.
1.3 Degaussing circuit
When the power is switched on, the CRT is degaussed automatically by current flowing through the degauss circuit
while the relay (S99R) is closed. Degaussing current flows for approximately 20 seconds and stops by causing relay
(S99R) to be opened after secondary circuit operation is stabilized.
The circuit also allows for manual degauss by using “DEGAUSS” control on OSD menu which closes S99R through
Q991 to allow current to flow through the degauss coil.
7
AC inlet
FIG. 6 BLOCK DIAGRAM FOR POWER SUPPLY CIRCUIT
Main power supply
Circuit #2
Chopper
Chopper
Control
+B
+85V
+54V
+14V
Circuit #1
Degauss
Circuit
Manual
Degauss
Circuit #3
+ 12V
Chopper
On/Off
control
5V
Reg.
+ 6.3V
MPU
Control
Standby power supply
On/Off
On/Off
control
Heater
8
2. Video Processing Circuit
Amp
p
2.1 Video select circuit (Optional)
Two of Video input signals shall be switched at Video selector (I205) controlled by switching signal coming from
microprocessor.
2.2 Video Processor
The video input signal of 0.7 Vp-p is amplified to approximately 50 Vp-p by the video processing circuit and is fed to the
cathode to drive the beam current.
This chassis incorporates a single chip video processor I201, with three channels, one for each of R/G/B, which
functions as the pre-amp of the inputs, OSD mixer and also gain control. A control signal from the microprocessor
changes the amplifier gain of the video channels (R/G/B) together with white balance control.
Video Output circuit I202 amplifies R/G/B signals controlled by I201 to the enough level to drive Cathode of CRT. DC
voltage of Cathode is determined by DC Cut off voltage from Cathode Clamp Circuit. DC Cut off voltage is generated at
Level Shift Circuit which consists of I203, Q22R, Q22G and Q22B, whose R/G/B channels are also controlled by
microprocessor.
2.3 ACL Circuit
The current at the secondary winding of the flyback transformer is used to represent the CRT beam current. The current
is measured and fed to the contrast control Q281,Q282 to limit the maximum beam current with negative feedback.
2.4 Blanking Circuit
Video blanking during the beam retrace period is achieved by applying both horizontal and vertical blanking pulses to
I201.
2.5 Precedence of Clamp Pulse Circuit
Video Processor I201 receives Clamp pulse signal from I701, Precedence of Clamp Pulse Circuit.
2.6 OSD Circuit
I301 receives H/V pulses from Deflection Circuit and control signal from microprocessor, whose output feeds Clock
signals synchronized with H pulse and control signals from microprocessor, OSD display signals in R/G/B, OSD
blanking signal to OSD Mixer Circuit in I201.
FIG. 7 VIDEO PROCESS CIRCUIT
Video in to CRT
Video Processor I201
Gain
Control
Amp. Clamp
Level
shift
ACL
I701
Output
.
Cathode
clam
Cathode
R/G/B Gain
Control
Contrast
Control
From FBT
Brightness
Control
R/G/B Cut off
Control
9
)
8Buffe
e
t
)
3. Horizontal Deflection and High Voltage Regulation Circuit
3.1 Horizontal Deflection Circuit
The purpose of the horizontal deflection circuit is to cause the CRT electron beam to be scanned horizontally by driving
a current through the deflection yoke, synchronized by the H sync pulse. The circuit consists of an AFC circuit, made up
of an H phase locked loop and VCO (voltage controlled oscillator), and the deflection output.
The H.sync. signal is input to I701 where it is delayed and then input to a phase detector. The phase locked loop (I701)
also accepts input from a saw tooth waveform which is provided by the deflection feedback (flyback pulse) through the
R707. The output of the phase detector creates an error voltage between the feedback pulse and the input pulse and is
then fed to the VCO after processing by an AFC Filter.
If the oscillator frequency deviates more than 4% of H.SYNC, PLL1 (I701) goes into search mode and HUNLOCK (I701)
changes to “H”. The minimum horizontal frequency is determined by the capacitor at C706 and R704. Horizontal
frequency range is determined by R705. H.SIZE, S.PIN and Trapezium are controlled by PWM circuit (Q801). The
output pulse from the VCO is fed to the pre-drive and then output from I701 to the drive buffer Q701 / Q702. The
pre-drive circuit within I701 is controlled by duty cycle by the internal circuit.
In case of no sync signals supplied or excessive frequency change, such as a signal timing change, HUNLOCK once
changes to “H”, and PWM circuit (Q801) output is stopped.
The deflection circuit of the DJ72 chassis has been separated from the high voltage regulation circuit to provide
improved H linearity performance by utilizing the consonant conditions of the horizontal beam current characteristics.
The S-consonant capacitors, C770C777, are changed by Q767Q771 and S77R, which provide 812 stages of
consonant conditions. The horizontal linearity coils L771L772 are changed by S77R to provide two stages of H
Linearity conditions.
The H.DEF +B voltage chopper power supply parabolically modulates the H.DEF +B voltage of the deflection circuit,
based on the horizontal frequency, to provide a frequency - dependent voltage of between 42.5V and 160V to the
deflection circuit.
HFLB
V.SYNC
H.CP
V.BLK
From MPU
H.SYNC/Composite SYNC
MPU
FIG. 8 HORIZONTAL DEFLECTION CIRCUIT
I701
14
SEPA
RATER
SDA
SCL
+B (+200V
16
19
18
15
17
H.SIZE CONTROL
OSCILLATOR
5 3 4 6
Drive
Buffer
E / W
From
H.SIZE
PWM
H.Cen
MPU
32
12
13
I601
Vertical
Output
f
H-V
Def
Out
Amp
Amp
Driv
r
H.DRIVER
+B E
V.DY
Lin.
Coil
(85V
PWM
E
HV
Module
Lin.
Coil
T751
T751
L771
ERROR
S77R
C771~
Q767~
Q771
10
C777
From MPU
S.fig.
Cap.
S.fig.
Cap.
C770
From MPU
Select Select
V-sync
clamping
blanking
HUNLOCK
SDA
SCL
I701
14
16
17
19
18
FIG. 9 DEFLECTION CONTROL IC BLOCK DIAGRAM
EWDRV
11
EW-Output
H-Pincushion
H-Corner
H-Trapezium
-
V-Sync
Integrator
Video
Clamping
And
V-BLANK
HUNLOCK
Output
I2C-BUS
Receiver
Vertical
Oscillator
and AGC
V-Position
V-Size,VOVSCN
Protection
and Soft Start
I2C-BUS Registers
7V
1.2V
V-Output
V-Linearity
V-Linearity Balance
FOCUS
Horizontal
and Vertical
H-Size
Control
12
13
32
6
4
3
5
V
OUT2
V
OUT1
Focus
H-Size
Control
Oscillator
H/C-sync
15
H/C-Sync
Input and
Polarity
Correction
Coincidence
Detector
PLL1 and
H-Position
Horizontal
Oscillator
H-Output
Stage
PLL2,Parallelogram,
Pin Unbalance and
Soft Start
1
HFLB
HDRV
8
11
FBT
3.2 High Voltage Regulation Circuit
The output pulse from Q701 is also fed to the high voltage regulation circuit with the same design of consonant circuit as
the horizontal deflection circuit. High voltage of 27.0 kV is obtained by the step-up windings of the flyback transformer to
drive the CRT anode. The high voltage is monitored by the E
error detection circuit. The error detection circuit
HV
functions by stepping the high voltage down and comparing it with the reference voltage of inside I740 whose output
controls I740, the Integrated Circuit included with E
switching transistor.
HV
3.3 Dynamic focus drive circuit
This monitor’s CRT includes a dynamic focusing electron gun to achieve sharp and uniform focus throughout the display
area. The CRT’s Focus anode receives a DC component of approximately 27% of the CRT anode voltage, combined
with the AC voltage parabolic wave form of magnitude of 600 Vp-p horizontal, and 180 Vp-p vertical. DC focus voltage is
obtained from a tap of the flyback transformer’s bleeder resister, and fed to G3 focus electrode. Horizontal and vertical
parabolic output pulses are amplified at Q501Q508, T560 and fed to the flyback transformer where they are combined
with the DC component (27% of anode voltage). The potentiometers (focus 1, focus 2) at the flyback adjust the DC
focus voltage. The focus 2 potentiometer mainly adjusts horizontal beam shape (vertical line width), and the focus 2
potentiometer mainly adjusts the vertical beam shape (horizontal line width) by optimizing the DC component of the
parabolic waveform.
3.4 High Voltage Hold-Down Circuit
DJ72- Chassis uses a system that stops H/V DRIVE SIGNAL output when abnormal high voltage is detected. So that
the high voltage output will be declined to zero. The circuit operation in detail is as follows.
When an input voltage to I740 (pin15, it is determined by R792 and R793) exceeds the specified level, the high voltage
is declined to zero.
FIG.10 HIGH VOLTAGE HOLD-DOWN CIRCUIT DIAGRAM
For the models CM771U-511, CM771ET-301
8
10
E
HV
I740
module
EHV +B
R792 R791
R793
+
C791
-
D790
L791
HIGH
VOLTAGE
CRT
R746
R756
R747
12
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