MEDION
Service Manual
17-inch Color Monitor
C1786PNST (MD 1786LH)
Service Manual Versions and Revision
No. Version Release Date Revision
1. 1.0 July 31, 2001 Original release
Copyright
Copyright 2001 LiteOn Technology Corp.
All Rights Reserved
This manual may not, in whole or in part, be
copied, photocopied, reproduced, translated, or
converted to any electronic or machine readable
form without prior written permission of LiteOn
Technology Corp.
C1786PNST (MD 1786LH) Service Manual.
Printed in Taiwan.
Trademarks
LiteOn is a registered trademark of LiteOn
Technology Corp.
All other trademarks are the property of their
respective owners.
MEDION
MD 1786LH (C1786PNST)
Table of Contents
1. Precautions.........................................................................................................2
2. Product Specifications .......................................................................................5
3 Control Location and Functions ...................................................................... 10
4. Operation Theory.............................................................................................. 11
5. Alignments and Adjustments ........................................................................... 16
6. Troubleshooting............................................................................................... 20
7. Recommended Spare Parts List ....................................................................... 27
8. Block Diagram ................................................................................................ 29
9. Exploded Diagrams .................................................................................. Inserted
10. PCB Diagrams ......................................................................................... Inserted
11. Schematic Diagrams ................................................................................ Inserted
Page 1
MEDION
MD 1786LH (C1786PNST)
1 Precautions
Follow these safety and servicing precautions to prevent damage and to protect against potential hazards
such as electrical shock and X-rays.
1-1 Safety Precautions
1-1-1 Warnings
1. For safety purpose, do not attempt to modify
the circuit board, and always disconnect the AC
power before performing servicing on the
monitor.
2. Operation of the monitor outside its cabinet or
with the cover removed involves the risk of
shock hazard. Repair work on the monitor
should only be attempted by service personnel
who are thoroughly familiar with all necessary
safety precautions and procedures for working
on high voltage equipment.
3. Do not lift the CRT by the neck. After
completely discharging the high voltage anode,
handle the CRT only when wearing shatterproof
goggles. Try to keep the CRT away from the
body during handling.
4. High voltage should always be kept at the rated
value, no higher. Only when high voltage is
excessive are X-rays capable of penetrating the
shell of the CRT. Operation at high voltages
may also cause failure of the CRT or high
voltage circuitry.
nonmetallic control knobs, insulating materials,
cabinet backs, adjustment and compartment
covers or shields, isolation resistor-capacitor
networks, mechanical insulators, etc.
3. AC Leakage Current Check
Always perform the AC Leakage Current
Check on the exposed metal parts, including
metal cabinets, screwheads and control shafts,
as follows:
a) Plug the AC line cord directly into a rated
AC outlet. Do not use an isolation
transformer during the check.
b) Use an AC voltmeter with at least 5000
ohms per volt sensitivity as follows:
Connect a 1500 ohms, 10 watt resistor
paralleled by a 0.15uF AC capacitor in series
with all exposed metal cabinet parts and a
known earth ground, such as electrical
conduct or electrical ground connected to
earth ground, as shown in the Figure 1-1.
Measure the AC voltage across the
combination of resistor and capacitor.
Figure 1-1. Set Up For AC Leakage Current Check
5. The CRT is especially constructed to limit Xray emission to 0.5mR/HR at 300 microamperes
anode current. To ensure continued X-ray
protection, replace the CRT with only the same
or equivalent type as the original, and adjust the
anodes voltage to the designated maximum
rating, never to exceed.
1-1-2 Safety Checks
Before returning the monitor to the user, perform
the following safety checks:
1. Inspect to make certain that each lead dress is
not pinched or that hardware is not lodged
between the chassis and other metal parts in
the monitor.
2. Inspect all protective devices such as
To kn o w n
earth ground
0.15ufd
1500 ohm 10 watt
To ex posed m e tal
cabinet part
c) Reverse the AC plug at the AC outlet and
repeat the steps for AC voltage
measurements for each exposed metal part.
d) Voltage reading must not exceed 0.3 volts
RMS, equivalent to 0.2 milliampere AC. Any
value exceeding this limit ill constitute a
potential shock hazard and must be
corrected immediately.
PrecautionsPage 2
MEDION
MD 1786LH (C1786PNST)
1-1-3 Product Safety Notices
Many electrical and mechanical parts in this chassis have special safety-related characteristics which are
often not evident from visual inspection, the protection afforded by them may not be obtained by replacing
them with components rated for higher voltage, wattage, etc. Before replacing any of these components,
consult the Recommended Spare Parts List given at the end of this manual. Any of the replacements that do
not provide the same safety characteristics may result in shock, fire, X-ray emission or other hazards.
1-2 Servicing Precautions
Warning: An electrolytic capacitor installed with the wrong polarity might explode.
Caution: Before performing servicing covered by this service manual, read and follow the Safety Precautions
section of this manual.
Note: If unforeseen conflict between the following servicing precautions and any of the safety
precautions, always follow the safety precautions
1. Follow closely the servicing precautions printed on the monitor cabinet and chassis.
2. Always unplug the AC power cord from the AC power source before removing or installing any component
or assembly, disconnecting PCB plugs or connectors and connecting a test component in parallel with a
capacitor.
3. When replacing parts or circuit boards, clamp the lead wires around the component before soldering.
4. When replacing a high wattage resistor (>0.5W metal oxide film resistor) in the circuit board, keep the
resistor about 1 cm (1/2 inch) away from the circuit board.
5. Keep wires away from the high voltage or high temperature components.
6. Keep wires in their original positions so as to minimize interference.
7. Always connect a test instruments ground lead to the instrument chassis ground before connecting the
positive lead; always remove the instruments ground lead last.
After putting the rear cover back and make sure the monitor is working properly, the Hi-Pot &
Ground Continuity tests MUST BE performed before the monitor is returned to user.
1-3 Hi-Pot Test
1. Test Equipment
Puncture test model PM5530 ADT or KIKUSU TOS-8750 voltage tester or equivalent approved equipment.
Note : The test equipment must be calibrated in regular period.
2. Test Setup
a) Apply voltage : DC 2100 VDC
b) Test duration : 3 seconds
c) Cutoff current should be set to 3 mA
3. Test Procedure
a) Unplug power cord from AC source.
b) Put the power switch of the monitor in the ON position.
c) Leave signal cable un-connected.
Precautions
Page 3
MEDION
d) Plug monitor power cord to the Hi Pot tester terminals.
e) Turn on tester and watch the indicator or beeper.
f) If the indicator lamp lighten, or beeper beeps, the test fails.
1-4 Ground Continuity Test
1. Test Equipment
AC low ohm tester TOS-6100 or equivalent approved equipment.
Note : The test equipment must be calibrated in regular period.
2. Test Setup
a) Test duration : 3 seconds
b) Set current limit at 25 A
c) The grounding resistance must be less than 0.1 ohm.
3. Test Procedure
a) Plug the monitor power cord to the tester terminals.
MD 1786LH (C1786PNST)
b) Make sure all connections are well-contacted.
c) Turn on monitor power and tester power.
d) Press Test button.
e) If green light shows up, means test OK.
If red light shows up, means test fails.
f) If the Tester has a digital display, the resistance value must not exceed 0.1 ohm.
Note : Be sure not to touch the metal portion of the signal cable head during testing.
PrecautionsPage 4
MEDION
2 Product Specifications
2-1 Specifications
17-inch (15.8-inch Visual image area), sloted mask, 90 degrees
Picture Tube
deflection, dot type black matrix, medium short persistence
phosphor, dark tint, non-glare/ anti-static screen,
0.27 mm dot pitch
MD 1786LH (C1786PNST)
Sc anning Frequency
Maximum Resolution 1280 dots (H) x 1024 lines (V) @75Hz refresh rate
Display Area 310 mm (H) x 230 mm (V) typical
Display Characters 80 char. x 60 rows on a 10 x 10 matrix
Disp la y C olors Analog
Input
Sync hronizatin Signals Se parate Sync: horizontal/vertical, TTL, positive or negative
Sync hronization
Frequencies
Signal Connectors 15-pin, D-shell connector
Video Signals Analog : 0.7 Vp-p, RGB positive
Power Input 75 Watts (maximum) AC rated voltage, 100VAC to 240VAC
Misconvergence Center Area : <
User Contro ls Po wer On/O ff, C o ntrast, Brightness, Horizontal Size, Horizontal
VGA, Super VGA, 1024x768@60/75/85/100 Hz
1280x1024@60/75 Hz
Unlimited Colors
Horizontal : 30 to 86 kHz
Vertical : 50 to 120 Hz
0.25 mm; Corner Area : < 0.3mm
Position, Vertical Size, Vertical Position, Pincushion, Trapezoid,
Rotation, C olor tempera ture, Language, Display Frequency,
Degauss, Recall, H. Moire,V. Moire, Pincushion Balance,
Parallel, OSD Position, Top Corner, Bottom Corner
Service Controls PWB-1613
PWB-1611 : power voltage adjust (VR801), high voltage adjust
Preset Modes 14 (see Table 2-2. Timing Chart)
o
Environmental
Considerations
Operation temperature : 10
Operation Humidity : 20% to 80% ambient
Storage temperature : -40
Storage Humidity : 10% to 90% (non-condensing)
Altitude : Non operating 40,000 feet sea level
operating 10,000 feet sea level
C to 40oC ambient
o
C to 65oC ambient
Note: Above specifications are subject to change without prior notice.
Product Specifications
Page 5
MEDION
2-2 Signal Cable Pin Connections
Table 2-2. Signal Cable Pin Assignment
Pin Signal Pin Signal
1 Red video 9** +5V
2 Green video 10 Digital Ground
3 Blue video 11 Ground
4 Ground 12 S DA
5* NC 13 H-Sync
6 Red gro und 14 V- Sync/VCL
7 Green gro und 15 S C L
MD 1786LH (C1786PNST)
8Blue ground
Note * This pin is used for selftest detection. Connect this pin to ground at the PC end.
** For PC 99: This pin will provide +5V from PC side.
Product SpecificationsPage 6
MEDION
MD 1786LH (C1786PNST)
2-3 Timing Chart
This section describes the timings that the computer industry recognizes as standard for computer-generated
video signals.
Table 2-3. Timing Chart
MODE 1234567891011121314
H. Dots 720 640 800 640 800 1024 800 1024 800 1280 1024 1024 1280 1280
V. Lines 400 480 600 480 600 768 600 768 600 1024 768 768 1024 960
H. Freq. (KHZ) 31.47 31.47 37.88 43.27 46.8 48.36 53.67 60.02 62.966 64.34 68.68 80 80 85.938
V. Freq. (HZ) 70.08 59.95 60.32 85 75 60 85 75.03 99.472 60 85 100 75 85
A Period (us) 31.78 31.78 26.4 23.11 21.333 20.68 18.63 16.66 15.876 15.55 14.56 12.376 12.504 11.636
B Blking (us) 6.356 6.356 6.4 5.33 5.172 4.923 4.409 3.657 4.028 3.589 3.725 3.624 3.022 3.017
C Sync. (us) 3.81 3.81 3.2 1.556 1.616 2.092 1.138 1.219 1.185 0.972 1.016 1.231 1.067 1.077
D B.P. (us) 1.907 1.907 2.2 2.22 3.232 2.462 2.702 2.235 2.37 2.248 2.201 2.12 1.837 1.508
E Active (us) 25.42 25.42 20 17.78 16.162 15.75 14.22 13 11.848 11.96 10.836 8.752 9.481 8.62
F F.P. (us) 0.636 0.636 1 1.556 0.323 0.369 0.569 0.203 0.473 0.374 0.508 0.273 0.119 0.431
G Peroid (ms) 14.27 16.68 16.58 11.76 13.333 16.67 11.76 13.33 10.05 16.67 11.77 9.988 13.329 11.764
H Blking (ms) 1.557 1.43 0.739 0.67 0.533 0.786 0.578 0.533 0.544 0.642 0.582 0.483 0.525 0.593
I Sync. (ms) 0.064 0.064 0.106 0.069 0.064 0.124 0.056 0.05 0.048 0.047 0.044 0.074 0.038 0.035
J B.P. (ms) 1.08 1.02 0.607 0.578 0.448 0.6 0.503 0.466 0.48 0.501 0.524 0.397 0.475 0.547
K Active (ms) 12.71 15.25 15.84 11.09 12.8 15.88 11.18 12.8 9.526 16.03 11.18 9.505 12.804 11.171
L F.P. (ms) 0.413 0.35 0.026 0.023 0.021 0.062 0.019 0.017 0.016 0.094 0.015 0.013 0.013 0.012
CLOCK(MHZ) 28.3 25.1 40 36 49.5 65 56.25 78.75 67.5 107 94.5 117 135 148.5
Sync H
Polarity V
- - + - ++++++++++
+ - + - ++++++++++
Horizontal
C
E
Vid eo
D
Sync
A
H.Parameters:
A: Period B: Blanking Time
C: Sync Width D: Back Porch
E: Active Time F: Front Porch
Product Specifications
Seperate Sync
Ve r t i c a l
B
F
I
K
Vid eo
J
Sync
G
H
L
V.Parameters:
G: Period H: Blanking Time
I: Sync Width J: Back Porch
K: Active Time L: Front Porch
Page 7
MEDION
MD 1786LH (C1786PNST)
2-4 Display Power Management Signal (DPMS)
Note: These power-saving states exceed the Environmental Protection Agency (EPA) Energy Star
requirements.
Table 2-4. Display Power Management Signal (DPMS)
State LED Color H-Sync V-Sync Power
Cons umption
ON Green Pulse Pulse Normal
*
OFF Amber No Pulse No Pulse <5 watts
* For power consumption : 75W Max. (@ 230V AC, preset size and maximum light output condition)
2-5 TCO Version
The monitor meets the TCO 95/99, NUTEK energy saving, electric and magnetic field requirements.
Also it is compliant with TCO 95/TCO 99 labelling scheme.
The emission from magnetic and electric field must comply with the limits specified by the Swedish Board
for Measurement and Testing, commonly known as MPR 1990 recommendations. These limits are summarized in the Table 2-4.
Table 2-5. TCO 95 Emission Requirements
OCT/FLVOCT/FLE
dleiFcitengaMTn52Tn002
dleiFcirtcelEm/V1m/V01
egnaRycneuqerFzHk004~2zH0002~5
eulaVSMRSMR
ecnatsiDmc03mc03
citatsortcelE
laitnetoP
V005-/+V005-/+
The monitor is designed with selected CRT and carefully routed wires around CRT, make sure exactly the
same routing scheme is used when doing CRT replacement.
Product SpecificationsPage 8
MEDION
MD 1786LH (C1786PNST)
2-5-1 TCO 95 Version (Optional)
The TCO 95 scheme is for international and environmental labelling of personal computers. The labelling
scheme was developed as a joint effort by the TCO (The Swedish Confederation of Professional Employ
ees), Naturskyddsforeningen (The Swedish Society for Nature Conservation) and NUTEK (The National
Board for Industry and Technical Development in Sweden).
1)`Scope
TCO 95 touches on ergonomic qualities, emissions (electrical and magnetic fields), energy efficiency and
ecology (with demands for environmental adaptation for both the product and the production processes at
the manufacturing plant).
2) Environmental Requirements
The monitor abides by the environmental demands concerning restrictions on the presence and use of
heavy metals, brominated and chlorinated flame retardants, CFCs (freons), and chlorinated solvents, among
other things. The monitor is also recyclable.
3) Energy Requirements
The monitor also follows the energy requirements that, after a certain period of inactivity, the monitor shall
reduce its power consumption to a lower level in one or more stages.
4) Others
The monitor meets the strict environmental demands for the reduction of electric and magnetic fields,
physical and visual ergonomics and good usability.
Table 2-5-1. TCO 95 Visual Ergonomics
erutaeFdradnatSnoitpircseD
ytiraeniLsselro%1 ehtotderapmocsworrosnmulocfohtgnelniecnereffiD
.rotinomehtforetnecehthguorhtshtgnelgnidnopserroc
ecnanimuLyalpsiD)tsaelta(2m/dc001
ecnanimuL
ytimrofinU
sselro1:7.1 ehtnihtiwecnanimulnimotxamehtneewtebsioitarehT
.aeraevitcaelohw
2-5-2 TCO 99 Version
TCO 99 will append the color temperature and energy efficiency specification, also cover the environmental requirement.
Product Specifications
Page 9
MEDION
3 Control Location and Functions
(1) Displays menu & exits menu
(2) Confirms menu selection Scrolls
through menu to
(3) Choose an icon for adjust
MD 1786LH (C1786PNST)
(diagram the same )
(4) Ment/Adjusts level of se-lected icon
(5) Power LED
(6) Power ON/OFF switch
3-1 Front Panel
3-2 Front Panel Keys Functions
1. Function Key: Display the main menu, and exit the adjustment screen and save adjustments.
2. Decrease Key: Scroll across main menu, highlighting control to be adjusted. Decrease value of selected
control. Toggle between Contrast and Brightness adjustment screens.
3. Increase Key: Scroll across main menu, highlighting control to be adjusted. Increase value of selected
control. Toggle between Contrast and Brightness adjustment screens.
4. Select Key: Press once to display adjustment screen. Press again, for some controls, to toggle between
controls shown in pairs on main menu.
5. Power LED: Display different modes (ON, Standby, Ssuspend or OFF) of the monitor by showing
different color for each mode.
6. Power ON/OFF: To turn the monitor ON and OFF.
3-3 Adjustment Procedure
1. Press (6) key to turn on the monitor.
2. At normal condition, press (1)on the front panel to activate the on-screen manager (OSM) menu.
3. To select a user control, press (2) or (3) key repeatedly until the control is highlighted.
4. To adjust the value for a particular control, press (4), then press the (2) or (3) key to obtain the desired
value. There are a few parameters that do not require any adjustment, like Manual Degauss, Memory
Recall.
5. Some controls are grouped in pairs on the main menu. Press (4) key to toggle between them.
6. To save your adjustments and exit screen, press (1) key. The menu will automatically clear out from the
screen if no keys are pressed within 30 seconds.
Note: To enter the Internal Adjustment mode, press (1) & (4) keys simultaneously then press (6).
Page 10
MEDION
MD 1786LH (C1786PNST)
4 Operation Theory
This is a fully digital controlled multi-sync color monitor that is compliant with DDC1 and 2B Plug and Play
VESA standard and offers the following main features.
4-1 Main Features
1. Simplified design with minimum components.
2. The MYSON MTV212 M(A) 32 processor-- that has I
and brightness-- offers the functions for: (a) Contrast, (b) Brightness, (c) H-size, (d) H-position, (e) Vsize, (f) V-position, (g) Pincushion, (h) Trapezoid, (i) Pincushion Balance, (j) Parallel, (k) Top Corner and
(l) Bottom Corner.
2
C BUS controlled geometric correction, contrast
In addition, it also offers more functions as: (a) Sync. processor, I/P and O/P, (b) Mute, (c) Power saving
- Suspend & Stand-By, (d) Power saving override, (e) DDC1/2B, (f) I
signal cable (g) CS1/CS2/CS3/CS4 for linearity and size compensation.
3. Stores up to 10 factory preset modes and offers 8 user modes. There are 16 function icons at OSD. They
are controlled by two function keys and flywheel knob on front panel.
4. Powerful PHILIPS TDA4863 and TDA4841 present the following useful functions: (a) Pincushion, (b)
Trapezoid, (c) V-Position, (d) V-Size, (e) Verticals C and S correction -- factory adjust, (f) Pincushions
V. position correction, (g) Corner correction -- factory adjust, (h) Pincushion unbalance correction -factory adjust, (i) Parallelogram distortion -- factory adjust, (j) Moire cancellation, (k) X-ray protection,
and (l) Full horizontal and vertical auto sync capability.
5. Software controlled auto shut off function activated if fH < = 29 kHz and fH > = 86 kHz.
6. Full range AC input and simplified line filter design.
2
C Bus for auto-alignment through
4-2 Microcontrol Section
1. This monitor uses MYSON MTV212 M(A) 32 CPU. It contains a 8051 8-bit CPU core, 256 bytes of
RAM used as working RAM and stack area, 32k bytes of OTP ROM, 13-channel 8 bit PWM D/A
converter, 2-channel A/D converters for key detection saving I/O pins, internal H. sync and V. sync
signals processor providing mode detection, and an I2C bus interface. When H/V sync through D-Sub
signal cable enter pin 41 and pin 42, the CPU performs frequency / polarity detection and calculate and
send to H/V sync OUT. Then CPU reads the data from I703 and transfer to device 4841 and some DAC
in CPU, above operation takes about 500 ms.
2. There allowed 10 factory preset modes and 8 user modes. There are 15 functions, Contrast, Brightness,
H. Size, H. Position, V. Size, V. Position, Pincushion, Trapezoid, Rotation, H. Moire, V Moire, Pincushion
Balance, Parallel, Top Corner and Bottom Corner, all controlled by OSD icon which can be adjusted by
user.
3. The pin 27 and pin 28 are used for ATE function. When CPU receives C6 as slave address, it will operate
in ATE mode which is used for auto-alignment. After alignment the data will be stored in I703.
4. The user control parameters are selected by OSD icons, through two function keys and flywheel knob,
keys, they are detected by sensing the voltage through R710, R740, R741, R743, R716, R717 to pin 25, 26
and 15 of I701.
Operation Theory Page 11
MEDION
4-3 Deflection Section
1. I2C -- autosync deflection controller is TDA4841.
MD 1786LH (C1786PNST)
2. The TDA4841 is a high performance and efficient solution for autosync monitors. All functions are
controllable by I
control all functions.
2
C bus. SDA and SCL signals coming from microprocessor feed to pin 19 and pin 18 to
4-3-1 Horizontal Section
1. The oscillator is driven by the currents in R419 and R420. The minimum oscillator frequency is determined
by R419 and the maximum frequency is determined by R420.
2. Horizontal sync goes into pin 15 through R318. And horizontal flyback pulse goes into pin 1 through R401
and bypass filter C403 from pin 5 of FBT and R496 for HFLB loop.
3. Horizontal driver (pin8) O/P to Q401 via C410.
4-3-2 Vertical Section
1. Vertical sync goes into pin 14 through R317.
2. The free running frequency is determined by R301 and C301.
4-3-3 Vertical O/P section
1. The differential output currents from pin 13 of Vout1 and pin 12 of Vout2 can be directly coupled to the
vertical deflection booster pin 7 and pin 6 of TDA4863.
2. The TDA4863 has two output stages which are current driven in opposite phase and operate in combination
with the deflection coil in a full bridge configuration.
3. This IC is powered by two sets of positive voltage and one set of negative voltage. (+11.7V at pin 1, -11V
at pin 4, +40V at pin 2).
4-3-4 E-W/Trapezoid and H. Width Controls
1. The horizontal O/P stage uses diode modulator D419, D433, C411, C412, L409 and C418 for East-West
(Pincushion) Trapezoid and H. width controls.
2. The scan current is determined by B
is accomplished by Darlington pair Q418 and Q419 by coupling a parabola waveform from pin 11 of
TDA4841. The H. width / corner and trapezoid correction are also accomplished by this pin 11. The DC
level controls H. size. The AC level is combined with side pin and trapezoid corners functions.
+
minus Vm ( the voltage of C418) values and the pincushion control
4-3-5 X-Ray Protection
1. To avoid X-ray hazard, a DC voltage generated at pin 4 of FBT and rectified by D408, C432 and divided
by R403, R404 and R405 come into pin 2 of TDA4841.
2. If this voltage is higher than 6.39 V, then TDA4841 will be activated to float HUNLOCK (pin17), H.
DRV( pin 8), B DRV (pin 6), VOUT1 (pin 12), VOUT2 (pin13). After that all deflection circuit stop
working.
Page 12 Operation Theory
MEDION
MD 1786LH (C1786PNST)
4-3-6 G1, Blanking and Brightness
1. The vertical blanking signal comes from pin 16 of TDA4841. This pulse through Q405 amplified and
converted into negative pulse and sent to G1 for vertical blanking.
2. In protection mode or an out-of- range situation HUNLOCK will send 5 V pulse to cutoff Q407, then G1
will go down to -150V. During the mode change, Mute acts as same as HUNLOCKS.
4-3-7 Contrast Section
1. Contrast is controlled by I701 through I2C bus to I501 (LM1267) directly.
2. Beam current is detected through T402 (FBT) pin 7, C429, R449 and detected voltage feeding into Q432,
Q433, R436, R497, R459, C482 to control I501 pin 22 voltage. When I501 pin 22 voltage drops
below 4.1 V, the ABL function will happen.
4-3-8 H/V size breathing compensation
1. Beam current is sensed as above section (3-3-7 item 2) and this voltage routes through R451, R468, C470
then through R437 to I401 pin 31 for H. size compensation.
2. HV voltage is detected through T402(FBT) pin 11. C481, R4F4, R4F8, R4F9, Q428, R4G0, Q431, R4G1,
then through R302 to I401 pin 21 for V. size compensation.
4-3-9 Dynamic focus circuitry
The dynamic focus is applied to improve the corner focus performance, it includes horizontal and vertical
dynamic focus.
1. Horizontal dynamic comes from C413 and is amplified through T403, L405, H-DY, L402, C411, R417,
C450, C448, R435 and feed to FBT dynamic focus pin (T401 pin 12).
2. Vertical dynamic comes from I401 pin 32 through C315, R322, R326, R321, R323, Q301, R324, R325 and
feed to FBT dynamic focus pin.
4-4 Power Supply Section
4-4-1 AC Rectifier
The circuit can accept 90 V to 264 V AC input through D801~D804 bridge diodes and C808 filtering to get
DC 126 V~364 V for power conversion in T802.
4-4-2 Line Filter
It consists of C803, T801, C804, C805, C808, C819, C807, C817 and meets EMI regulation.
4-4-3 Power LED Status
1. The LED has 3 leads with common cathode to emit green and amber color light for different power
saving states. It is controlled by CPU.
2. Normal : Green light
Amber LED is off because CPU pin 30 is 5V and pin 31 is 0V, only green LED is turned on.
3. Off Mode : Amber light
CPU pin 30 is 0V and pin 31 is 5V, then green is off and amber is illuminated.
Operation Theory Page 13
MEDION
MD 1786LH (C1786PNST)
4-4-4 Auto Degaussing
When S801 turns on, pin 14 of I701 will send a signal to Q802 and turns on RL801 for degaussing. After 4
seconds, it will turn off RL801 automatically.
4-4-5 PWM Control
1. Start Up
The I801 (5S0765C) gets power from R807, R808, C830 and pin 3 voltage reaches 15 V for starting up.
The I801 starts oscillation at 20 kHz, pin 1 output to drive T802. Switching on, R819 set up an 15 V to
keep I801 working through D809 auxiliary voltage.
2. Regulation
The DC O/P voltage is proportional to the auxiliary voltage, so I801 pin 4 senses the feedback voltage
from the divider D806, R809, C810, VR801, Q803, Q801 and R821 to compare with the built-in 1.5 volts
reference voltage for error amplifier operation. Finally pin 4 can modulate the different duty cycle by
VR801 setting to achieve regulation purpose.
4-4-6 Synchronization
1. Normal Mode
The sync pulse from FBT (31 kHz~86 kHz) via R812, R811 and C815 to pin 5 of I801 to keep I801
synchronized with horizontal sync input frequency.
2. Power Saving Modes: Standby/Suspend
Because there is no pulse from FBT, so the free-run frequency SMPS works at 20 kHz by I801 itself.
3. Override
The horizontal free run frequency is about 63.2 kHz under override condition, SMPS is synchronized to
this frequency.
4-4-7 O.V.P.
If the auxiliary voltage is higher than 25 volts makes pin 3 of I801 is limited to have the OVP activated.
4-4-8 O.P.P.
The excess current of T802 through I801 pin 1, 2, make Vs>1.1V internal of I801, then limite the power.
4-4-9 Step Up Power Supply For FBT
1. The B+ of FBT is proportional to horizontal frequency, that is the higher frequency, the higher voltage.
The basic voltage is 49 volts from T802 pin 10 via L811, D813, C824 and the gate control of Q451 comes
from I401 pin 6 via Q450, Q434, D435 and R4E5. The duty cycle is controlled by I701 pin 33 (PWM pin
Adj.) via R719, C741, R4F6, R4F5, R4F1.
2. The regulation and boost up (from 56 V to 172 V or more, on demand). The H.V. is set at 25 kV (zero
beam) by I301 pin 33 which senses the secondary O/P from FBT. The booster comprises Q451, L410,
L411, D450, C425 and T802 to offer the required B+ for different frequency modes.
Page 14 Operation Theory
MEDION
MD 1786LH (C1786PNST)
4-5 Video Amplifier Section
1. RGB signal inputs are terminated by R501, R531 and R561 then pass through the coupling capacitors
C503, C533 and C563 to IC501 LM1267 preamplifier.
2. The amplifier RGB signals (0~3 Vpp) are adjusted by I
from pin 16 of TDA4841 to set up equal clamp level.
3. The video output stages are amplified by I502 (LM2467).
2
C bus, I501 pin 23 is for clamp pulse which comes
4. The RGB cathodes cut off are adjusted by I503 (LM2479) pin 8, 7, 6, which comes from I501 pin 16, 15,
14 to adjust cut iff voltage level by I
5. Under override condition, NO SIGNAL will show up on the screen.
2
C bus.
4-6 OSD (On Screen Display) Circuit
1. The I504 MTV021-08 is OSD IC. The OSD signals are worked by positive vertical pulse from I701 pin
34 that goes through R720 to I502 pin 10, and positive horizontal pulse from T402 pin 5 goes through R496
to I502 pin 5. CPU I701 pin 13, 12 (I2C bus) transfers information to I502 pin 7, 8.
2. The OSD R. G. B signals and blanking signal are terminated at I502 pin 15, 14, 13, and 12 to I501 pin 1,
2, 3 and 4 then the OSD picture appears.
Operation Theory Page 15
MEDION
MD 1786LH (C1786PNST)
5 Alignments and Adjustments
This section of the service manual explains how to make permanent adjustments to the monitor settings.
5-1 General Adjustments
5-1-1 Adjustment Conditions
a) Power Supply
Apply AC 115 V or 220 V
b) Warm-up Time
The monitor must be powered on for 15 minutes before starting any alignment, but requires 30 minutes of
warm-up time for convergence adjustment.
c) Signal Input
1. Video: RGB Analog, 0.7 Vp-p, positive
2. Synchronization: Horizontal and vertical TTL signal, separate, positive or negative
3. All adjustments should be made using a signal of FH = 86kHz, FV = 85 Hz, unless otherwise defined.
5-1-2 Equipment Required
The following equipments are necessary for adjustment procedures:
1. Volt-ohm-A meter (Sanwa FD-750C or equivalent)
2. 30 kV high voltage probe (HP34111A)
3. Oscilloscope (TEK2235 or equivalent)
4. Minolta Color Analyzer II
5. Signal generator (IBM PC with proper display cards or Chroma 2000)
6. Screwdriver
5-1-3 Switching Power Supply and Regulator Adjustment
a. The regulated B+ control has been preset in the factory and needs no adjustment. However, if any repair
is made on the power supply section, the following readjustment procedures are recommended:
1. Allow the monitor to warm-up for about 15 minutes.
2. Apply VGA (1280 x 960 @ 86 kHz/85 Hz) signal to the monitor.
3. Connect a DC voltage meter to TP001 (on the Main board), and adjust VR801 for 11.7 ± 0.1 Vdc
4. If a fuse is broken during adjustment, remember to replace it with the exact same type of fuse.
b. If necessary, follow the following procedures to enter the factory mode.
1. Press both ENTER key simultaneously then power ON.
2. After turn the power off, this monitor will go back to normal mode.
Page 16 Alignments and Adjustments
MEDION
5-2 Alignment Procedures
5-2-1 High Voltage Adjustment
CONDITION
MD 1786LH (C1786PNST)
Press
and 2 key simultaneously when switching the power On.
1
Display image : No video (86kHz Mode)
PROCEDURE
Connect DC meter to TP002 and adjust HV (i)
R802 to obtain a DC voltage of -152 ± 0.2 V DC (Sampo FBT) for CPT CRT M41AGE93X76 (TCO).
5-2-2 Screen and White Balance Adjustment
CONDITION
Press
Display image : No video (86kHZ Mode)
PROCEDURE
1 Raster color setting
1-a. Set brightness max. to 77 (OSD cursor) and 563 ± 5 at G2.
1-b Adjust R and B cutoff to min.
1-c Adjust G cutoff to about 0.45FL
1-d Adjust B cutoff to get y=283 ± 5, R cutoff to get x=298 ± 5 and Y=0.65 ± 0.05 FL.
1-e Adjust brightness cutoff to raster 0.01-0.02 FL.
and 2 key simultaneously when switching the power On.
1
CONDITION
Display image : 50 mm x 50 mm white block pattern
PROCEDURE
2 6500
0
K color temperature setting
2-a. Set brightness to cutoff and Contrast to maximum.
2-b Move cursor on OSD to choose color temperature icon.
2-c. With green block pattern, adjust G gain to get Y about 32FL.
2-d Adjust R.B. gain to get x=313 ± 5, y=329 ± 5; and Y=43 ± 0.5FL
3 9300
0
K color temperature setting
3-a. Set Brightness to cutoff and Contrast to maximum.
3-b Move cursor on OSD to choose color temperature icon.
3-c. With green block pattern, adjust G gain to get Y about 32FL.
3-d Adjust R.B. gain to get x=283±5, y=298±5; and Y=43±0.5FL
4 Full white ABL setting
Alignments and Adjustments
Page 17
MEDION
MD 1786LH (C1786PNST)
CONDITION
Display image : full white pattern
4-a Set Brightness to cutoff and Contrast to maximum.
4-b. Adjust ABL to Y=29FL ± 1FL.
4-c. Check the white balance at 5FL and 30FL.
4-d. Repeat all the procedures in 4-2-2 section until the best white balance is obtained.
5-2-3 Focus Adjustment
CONDITION
Display image : me character pattern (68.68 kHz Mode)
PROCEDURE
1. Set brightness to cutoff and contrast to maximum.
2. Adjust focus 1 at T402 (static focus VR) to make vertical line clear.
3. Adjust focus 2 at T402 (static focus VR) to make horizontal line clear.
4. Repeat above procedures to get best focus.
5-2-4 Static Convergence Adjustments
Static convergence involves alignment of the red, blue and green lines in the center area of the display.
Note : The monitor requires 30 minutes of warm-up time for convergence adjustment.
CONDITION
Display image : Crosshatch pattern
Warm-up Time : 30 minutes
PROCEDURE
1. Set brightness and contrast to display a well-defined pattern.
2. Ensure the convergence magnet rings are correctly positioned on the CRT.
Figure 5-1. Convergence Magnets on the CRT
1
11
+
P
CRT
FRONT
8 7 6 5 4 3 2
10
1) Setup Bolt 2) Bow Magnet 3) Band 4) 2-Pole Magnet
5) Spacer 7) Spacer
9) Holder
6) 4-Pole Magnet
9
8) 6-Pole Magnet
11) Tabs10) Band
3. Rotate the individual rings of 4-pole convergence magnets by changing the spacing between the 2 tabs to
Page 18 Alignments and Adjustments
MEDION
MD 1786LH (C1786PNST)
converge the vertical red and blue lines at the center of the screen.
4. Rotate the pair of rings of 4-pole convergence magnets by maintaining spacing between the 2 tabs to
converge the horizontal red and blue lines at the center of the screen.
5. Rotate the individual rings of 6-pole convergence magnets by changing the spacing between the 2 tabs to
converge the vertical red, blue and green lines.
6. Rotate the pair of rings of 6-pole convergence magnets by maintaining spacing between the 2 tabs to
converge the horizontal red, blue and green lines.
7. Repeat the steps from 3~6 until the best convergence is obtained.
Figure 5-2. 4-pole and 6-pole Magnets Movement
Red/
Bl u e Red
Bl u e Gr e en
Blue
Red
4-pole magnets
movem e nt
Red/
Blue
Green
6-pole magnets
movem e nt
Note : The 4-pole magnets and the 6-pole magnets interact, making dot movement complex.
5-2-5 Degaussing
Degaussing is required when poor color impurity appears on the screen. This monitor uses an automatic
degaussing circuit that is activated when the power is on. The automatic degaussing will be fully functional
again after the monitor has been in operation for 20 minutes.
The degaussing effect is confined to the picture tube since the coils are mounted at the back of the tube.
Should any part of the chassis or cabinet becomes magnetized, it is necessary to degauss the affected area
with a manual degaussing coil.
5-2-6 Manual Degaussing
1. Apply line voltage to the degaussing coil and move it in a rotary motion over the front, sides, and top of the
monitor. The coil should be kept away from the rear of the monitor to avoid damaging the magnetic neck
components.
2. Slowly rotate and move the coil away from the monitor to about 6 feet beyond the point where no effect
on the CRT will be noticeable.
For proper degaussing, it is essential that the field be gradually reduced by moving the coil slowly away from
the monitor. The degaussing coil must never be shut off or disconnected while near the monitor, as this would
introduce a strong field instead of canceling the effect of the stray fields.
Alignments and Adjustments
Page 19
MEDION
6 Troubleshooting
6-1 No Raster
MD 1786LH (C1786PNST)
No Raster
Measure
voltage of B+ at
T402 pin 2 on
PWB-MAIN
Yes
Check DC
B+ line, Q451,
Q402, T402
0 V
Short Circuit
at load?
No
Check voltage
of C808
Yes
Check
I801, R807,
R808, Q801,
Q802, ZD802,
VR801
Grid 1, Grid 2, etc.
No
Check D801,
D802, D803,
D804, T801,
R804, F801
Normal
(56 V, 31.5 kHz)
Check voltage of
cathode, heater,
High
(75 V or more)
Check I401,
I703, R719, C741,
R4F6, R4F5, R4C4
Page 20 Troubleshooting
MEDION
6-2 OSD Abnormal
MD 1786LH (C1786PNST)
OSD Abnormal
Check I502 pin 9, 4
is 5V and pin 5, 10, 7, 8
missing?
No
Check R517, L514,
R527, R523, R524
OK?
Yes
Check P502
OK?
Yes
No
No
Put on
I502
Replace them
Replace it
Yes
Replace I502
Troubleshooting
Page 21
MEDION
6-3 Function Key Abnormal
Function Key Abnormal
MD 1786LH (C1786PNST)
Check I701 and
I703 missing?
No
Power
ON/OFF again and
check X701, oscillator
OK?
Yes
Check
I703 EEPROM content
OK?
Yes
Yes
No
No
Put on
I701, I703
Replace X701
Replace I703 or do
ATE again
Replace I701 and check
uP OK?
No
Check
pin 8 of I701
is 5V?
No
Replace I705, Q701,
Q702, R728
Yes
Yes
Replace I701
Check
ZD701, R735
Page 22 Troubleshooting
MEDION
6-4 No Vertical Scan (Raster is one horizontal line)
No Vertical Scan
MD 1786LH (C1786PNST)
Check I301 voltage of
pin 1 is 12V, pin 4 is
-11V, pin 2 is 40V?
Yes
Check
pin 5 O/P waveform at
I301 ?
Yes
Check
pin 6, 7 of I301
waveform ?
No
No
No
Ckeck or replace
I301.
Check R312, R307,
R306, R313, R308,
R315, R316
Replace I401
Troubleshooting
Still no vertical scan
Check or replace CRT
Page 23
MEDION
6-5 Out of Horizontal Synchronization
Out of Horizontal
Synchronization
MD 1786LH (C1786PNST)
Horizontal
sync present at
pin 15 of I401
Yes
Check
I401 pin 8 H. output
frequency & pin 29
waveform
Yes
Check Q401,
T401, Q402,
R424, D401
6-6 Out of Vertical Synchronization
No
No
Check or replace
the signal cable or
H. sync pin 41
of I701.
Check or replace
I401, C406
Out of Vorizontal
Synchronization
Vorizontal
sync present at
pin 14 of I401
Yes
Check
I401 pin 24 waveform
Yes
Check I401 pin 12 & pin 13.
No
No
Check signal cable
& V. sync pin 42
of I701.
Check or replace
C303, I401,
Page 24 Troubleshooting
MEDION
6-7 R.G.B. Video Amplifier Abnormal
RGB Video AMP Abnormal
MD 1786LH (C1786PNST)
Check
waveform at I501 pin 5, 6 and
7
Yes
Check
waveform at I501
pin 18, pin 19
and pin 20.
Yes
Check
I502 pin 1, 2 and 3 collector
voltage (normally about 70V)
& waveform
Check or replace the
No
signal cable or I501
No
No
Replace I501
Replace I502
Troubleshooting
Yes
Video signal present at the
pin of the CRT R.G.B.
Cathode
Yes
Defective cut-off circuit
(DC restore) I504
Page 25
MEDION
MD 1786LH (C1786PNST)
6-8 Blank EEPROM Trouble-shooting:
Description of functions for models under C1786 series EEPROM DATA AUTO-RELOAD
The function allows plant staff to pre-write and customer service personnel to use blank EEPROM
through the pre-write EEPROM function whenever the CPU is implemented. The method of operation
is as follows:
First, press the HOT KEY, start after C1786 turns to (<&>) KEY. At this point of time, the CPU
is capable of detecting the first 8 DATA of each page that EEPROM contains. When the
reading goes to 00H or FFH, the EEPROM PAGE will turn to blank; instead, the pre-set value
is being written into the EEPROM through CPU. Otherwise, it shall be deemed an effective
value and that the pre-write function shall not be activated.
Page 26 Troubleshooting
MEDION
MD 1786LH (C1786PNST)
7 Recommended Parts List
Note:1. The components identified by mark are critical for X-ray safety. Replace these with
exactly the same parts specified.
2 . There is only OTP IC at the model beginning (FPR stage or before). When it put in mass
production and there must be Mask coming out. If you have spart parts need, please use BOM
to get the last release part number and related information.
No. Location Part Number Description
1 Q401 6421002705 TR NPN KSD1616A G TA
2 C808 6312618102 ALU uF 180 400V F 85C 25x35
3
4 D814 6412021702
5 D810 6412004117 DIODE UF2004M 2A/200V 50 nS
6 D815 6412002617 DIODE UF3002M 3A/100V 50 nS
7 D817 6412024404
8 F801 6851504053 FUSE TIME LAG H-BRK 4A/250V
9 I301 6442026400 IC TDA4863J 7P (PHILIPS)
10 I401 6442030000 IC TDA4841 32P SDIP (PHILIPS)
11 I501 6442031500
12 I502 6442029700 IC LM2469 9P NS
13 I503 6442029900 IC LM2479 8P NS
14 I701 6448014500 IC MTV212 M(A) S32 40P PDIP MYSON
15 I703 6448015720 IC MTV24C08 (MYSON)
D801 D802
D803 D804
6412010907 DIODE LT2A06 T52 2A/800V
DIODE
DIODE HER
IC LM
FE30-02BXF06
6 1A/600V 50 nS
10
24P SDIP (NS)
1267
16 I705 6442000875 IC KIA78L05 (SAMSUNG)
17 I801 6442031600 IC 5S 0765C 5P FAIRCH
18 L404 6111204135 COIL CHOKE 2mH K DR8x10
19 L405 6119007702 COIL LINEAR
20 L409 6111155133 COIL CHOKE 150uH DRWW 14x15 LY3B
21 L410 6111155138 COIL CHOKR L=150uH K DRWW 14x15
22 Q402 6421006700 TR NPN 2SC5587
23 Q418 6422002925 TR NPN HBF422T/B TO-92 TAPING
Recommended Spare Parts List
Page 27
MEDION
No. Location Part Number Description
24 Q419 6422006000 TR NPN 2SD2012 TO-220(IS)
MD 1786LH (C1786PNST)
25
26 Q451 6426006300 FET N-CHNL IRFS634A FAIRCH 11d
27 R803 6203080017 POSISTOR & OHM DGC2R08M
28 R804 6201100012 THERMISTOR 10 OHM 3A P=5 UEI
29 R802 6221127852 MOF OHM 0.27 1W J HOR
30 R4E3 6221227852 MOF OHM 0.27 2W J HOR
31 T401 6135000801 XFRMER HOR DRIVE THD-1008A EI19
32 T402 6133086010 FBT TFB-8601 SAMPO
33 T403 6136001700 XFRMER DYNAMIC TDF-1017 EI22 LSE
34 T801 6138001603 LINE FILTER TLF-1016C 16mH LSE
35 T802 6131052600 XFRMER PWR TPW-1088 EERL35 LSE
36 X701 6449006900 CRYSTAL 12.000 MHZ 49U 30PF TOP
Q420 Q421
Q430 Q403
6426010500 (S1)
6426006400 (S0)
FET N-CHNL IRF630MFP/IRFS630A
Page 28 Recommended Spare Parts List
MEDION
8 Block Diagram
MD 1786LH (C1786PNST)
SDA
SCL
SDA
SCL
R
G
B
R DAC
I501
PRE AMP
LM1267
RGB
O/R
V
H
SDA
SCL
G DAC
B DAC
R
G
B
MTV021
SDA
I701
MTV212M(A) 32
R
G
ABL
G1
BRIGHTNESS
CONTROL &
SPOT KILLER
DRIVER
GND
H
11.6V
B
CLBL
HFLB
SDA1
H
OUT
SCL1
VTTL
SW5 V
LM2479
R, G, B
BUFFER
&
DC
RESTORE
5V
ABL
5V
SW 5 V
OSD
SCL
6.3V
GND
115V
SDA 1
SCL 1
GND
V
H
80V
P503
11.6V
80V
I401
TDA4841
I502
Video AMP
LM2467
11.6V
BLANKING
CKT
GND
VIDEO 5 V
HFLB
G1
G2
P502
DIODE
MODULATE
G4
25.6KV
FBT
-150V
560V
6.6KV
115V
P501
RG
R
GG
G
BG
B
OSD
BLK
H
V
5V
SG
O/R
LED
KEY
CONTROL
POWER
DEL
CKT
11.7V
Q701, Q702
5V SW CKT
E2PROM
I703
LINE
FILTER
I705
78L05
BRIGHTNESS
DEG
CKT
BRIDGE
DIODE
5V
Q805
LOW VOLTAGE
DROP DOWN
6.3V
5S0765C
I801
SMPS
POWER
O/P
TRANS
T802
VERTICAL
O/P
I301
-11V
TDA4863J
11.7V
Q813
6.3V
49V
80V
Vertical Focus
STEP
UP
CKT
+H
49V
-H
+V
D.Y
-V
49V
XRP
11.6V
Q811
Q805
5V
dynamic
foucus
Block Diagram
Page 29
MEDION
LITE-ON TECHNOLOGY CORP.
5 F, No. 16, Sec. 4, Nanking E. Road, Taipei, Taiwan
Tel: 886-2-25706999Fax: 886-2-25706888
URL:// www.liteontc.com.tw
Printed in Taiwan
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