SERVICE MANUAL
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MODEL
VM-1201
A0
REVISION
DATE
MAY. 21. 2001
DOCUMENT NUMBER
2.4 VERTICAL DEFLECTION BLOCK.........................................……………………..………...
2.5 HORIZONTAL DEFLECTION BLOCK.............................……………………............……...
3. TROUBLESHOOTING INSTRUCTIONS............................................……………...…….…..
3.1 NO DISPLAY, NO POWER.......................……………………………………………………..
3.2 NO DISPLAY, (POWER OK)............…………………………………………………………..
3.3 NO DISPLAY, (NO ASTER) ……………………………………………..........……………..
3.4 NO PICTURE OR NO COLOR (RASTERK)..................………………………...………….
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3.5 VERTICAL DEFLECTION FAILURE............................................…………………..……….. 10
APPENDIX：
A. SPARE PARTS LIST
B. SCHEMATICS AND PCB LAYOUT DIAGRAM
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Audience
This service manual is primarily for system / service engineers, distributors and dealers. It carries the
assumption that the reader understands the basic operating concepts.
Purpose
This manual contains reference data for Speco Technologies monitor. It gives information regarding
the operating principles of monitors, as well as technical service and maintenance information.
1. Introduction
The VM-1201, high performance monochrome monitor, display over 1,000 TV lines resolution on a
bright 12-inch picture tube. This combination provides excellent multi-screen displays commonly
produced by picture-in picture and quad units.
All user controls are conveniently located behind a protective front panel door. This monitor can be
placed on a desk or mounted in a standard 12-inch rack (with an optional rack mount kit)
This series are housed in an enameled steel cabinet for ruggedness and durability, and with the exception
of the picture tube, the circuitry is all solid-state. It also feature video loop through connectors with
switchable high-z/75ohm termination.
The VM-1201 is an excellent choice when you require a rugged, compact B/W monitor. The exquisite
and reliable design of this monitor will provide years of trouble-free operation.
1.1 Operational Specification
1.1.1 Operating Environment
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Temperature
Operating ：-10 to + 50℃
Storage
：-20 to +70 ℃
Humidity (Relative)
Operating ：10 to 85% non-condensing
Storage
：10 to 95% non-condensing
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1.1.2 Signal Input Requirements
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Connector
For CVBS：BNC terminal
Type：composite video input
Synchronous：0.3 V
Level：1.0Vp-p
Luminance：0.7V
Polarity：Positive bright
Impedance：75 ohms
1.1.3 Power Input Requirements
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Operating Voltage Range：90 ~ 264 VAC at 50 / 60 ±3Hz
Input Current at 90 VAC
Operating：0.5 Amps rms. maximum
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Input Current at 264 V
Operating：0.3 Amps rms. maximum
Power consumption
Normal operation：30 Watts maximum
1.2 Functional Specification
The standard conditions for verifying the following specification are as below：
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• Temperature
• Magnetic field
• AC line Input
• Warm-up Time
• Ambient light
：25 ±5℃
：No additional magnetic field in near side
：100 ~ 240 VAC ±10%, 50/60 ±3Hz
：30 minutes min. after power on and signal applied
：400 to 600 lux.
1.2.1 Display Quality
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Display area (monoscope pattern)：full scan
Video Amplifier Performance
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Video Bandwidth
：8 MHz
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Light output (brightness and contrast at maximum)
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At block pattern
：100 FL minimum
At full white pattern ：50 FL minimum
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Contrast adjustment range：Over 12 dB
Linearity (cross pattern)
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Horizontal ：10% maximum
Vertical
：10% maximum
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Picture geometry：≦ 2.5%
Picture centering：≦ 6mm
Size stability：Picture luminance from 5 FL to max., the size shall be less than 2.5%
(with full white pattern)
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Swing and jitters：Swing and jitters are not allowed (viewed at 50cm from eyes to
screen).
Focus：(viewed at 50cm from eye to screen, contrast adjusted to set luminance at 20 FL
with full white pattern, brightness set at raster just disappeared) Inspect full
character pattern, all characters should be distinguished.
1.3 Controls and adjustments
• External user’s controls：
• Brightness adjustment
• Contrast adjustment
• Horizontal hold
• Vertical hold
• Volume adjustment (optional).
1.4 Physical Specifications
• Dimension：313mm(H) ×310mm(W) x300mm(D)
• Net Weight：9 Kg
2. Theory of Operation
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This section describes each functional block of the monitor.
2.1 Main Power Supply Block
• AC power input：AC socket
• Line input noise / EMI filtering：Line filter T902 ;
X-Cap C901, C902.
Y-Cap C903, C904, C905.
• Over current protection：Fuse
• Power on/off control：Power switch
• AC to DC conversion and filtering：Diode D901, Capacitor C906
• Start-up circuit：R914, C914.
• Main switching power controller, free run oscillation, voltage feed back, switching duty control,
cycle by cycle over current protection, power MOSFET driving：U901-UC3842
• Free run oscillation：R909, C910.
• Voltage feed back and control：output voltage control R910, R911 & VR901; gain compensation
C911& R903.
• Current sensing and cycle by cycle over current protection：Current sensing R904; Noise
filtering R906, C909.
• Energy storing and transferring：Power transformer T901.
• Power driving：Power MOS transistor Q901.
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• Snubber circuit：Snubber C907, D902, R902.
• Primary side self-powering circuit：D903,C914.
• Output 13.5 volts for vertical & horizontal drive circuits：D904, C915.
• Output 27.5volts for horizontal deflection circuit：D906 ,C916.
2.2 Video input block
• Signal input buffering and switch
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CVBS Input buffer ：Q201 & R201,R202.
• Video filter & output stage.
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Video input：Through C202 to W202 (Contrast VR ) and differential amplifier Q202,
Q203.
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Video amplifier: Cascade amplifier R219, Q204, Q205, R222, C206.
Brightness control:VR201, R214, R225, R226, Q204.
2.3 Vertical & horizontal processor
2.3.1 Vertical guard:
This vertical feedback signal on pin2 when the level on pin 2 is below 0.35v or high
than 1.85v the guide circuit inserts a continuous level of 2.5V in the sandcastle output
signal of pin 17.The results in the blanking of the picture displayed, thus preventing a
burnt-in horizontal line.
2.3.2 Vertical drive output:
The drive o/p pin1 of U401 delivers a drive current of 1.5mA at 5V output through R302
to U402 pin1.
2.3.3 Sync separator:
The video input through C401, R401 and filter C402 to pin 5 of U401.The Sync separator
is designed such that the slicing level is independent of the amplitude of the Sync pulse. The
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black level is stored at pin7 by C404. The slicing level is stored at pin6 by C403 and decided
by R403.
2.3.4 Phase detector:
The phase detector circuit is connected to pin8. The circuits are activated depending on
the voltage of pin18 and the state of the Sync pulse noise detection circuit, C405, C406,
R405.
2.3.5 Supply (pin9, 10 and 16):
U401 can start operating by application of a very low supply current into pin16. When the
starting circuit is taken from pin10 via internal diode, and the voltage on pin16 will stabilize
to a typical value of 9.4V
2.3.6Horizontal oscillator, horizontal output transistor, and second phase detector (pin11, 12,
14 and15):
The oscillator is connected to pin15. An external RC; C409, R412, VR401; sets the
frequency combination between pin15 and ground. The open collect horizontal output is
connected to pin11. The duty factor is set by an internal npn emitter follower stage
connected to pin14. When no flyback pulse is detected at pin12 the duty factor of the
horizontal output stage is set to 50%.
2.3.7 Mute output and 50/60HZ identification (pin13):
Pin13 has the possibility for 50/60HZ identification. A pull-high resistor R408 achieves
the function.
2.3.8 Sandcastle output (pin17):
The sandcastle output pulse generated at pin17.
2.4 Vertical Deflection Block
• Power amplifier：
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The DC level across C308 and the current is detected by R306 and feedback to U401
through R311.
The driver output comes from pin5 and it drives the yoke by a negatives slope current ramp
R419 is used to stabilize the power amplifier.
Boost power D301, C305 is connected to pin3.
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• Flyback generator：
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U301 pin6 is the output of the flyback generator that when driven, jumps from low to high
condition C305 transfers the jump to pin3
• Vertical size control：VR301, R312, R308.
2.5 Horizontal Deflection Block
• Horizontal drive buffering：Driving source-U401 pin11. Driving transistor-Q40, to pull high the
driving waveform to drive the Q401(MOS FET).
• Horizontal deflection：Horizontal Output transistor-Q401; Load-Yoke inductance and C414 ;
D401, High Voltage generation-flyback transformer .
3 Troubleshooting Instructions
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This chapter describes possible failures of the monitor with corresponding check/correction
actions, and guidelines for safe operation and service of the monitor.
3.1No Display, No Power
3.1.1First of all, turn power off, use multimeter to check Q901, and R904, replace if bad. Turn
power on after that.
3.1.2Check DC voltage across C906. If no voltage or voltage too low, check and fix the following
components：AC receptacle poor contact, fuse F601 broken, power switch malfunction, or
bridge diode D901 bad
3.1.3Check voltage on U901 pin 7 for start up condition：If voltage on U901 pin 7 reaches the start
up voltage(around 15 to 17.5V), U901 UC3842 will start to work and output 5V at pin 8. If
voltage on U601 pin 7 is too low, check and fix following circuits：start up circuit R914,
and C914.
3.1.4If no output pulses at U901 pin 6, check and replace U901.
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3.1.5If driving pulses at U901 pin6 and drain of Q901 are correct but voltage at U901 pin 7 low
than threshold voltage --causing U901 to stop and restart periodically, check and repair
following circuits. Power transformer T901 bad; D903 short-circuit/opened.
3.2No Display, power output normal.
3.2.1Check and fix FBT B+：If no B+（27.5V）on pin2 of FBT replace D906, C916.
3.2.2Check driving output voltage：0 or very low check and replace Q402, Q401.
3.2.3Power off monitor. Check yoke connection. Use multimeter to check D501, D502, D401, Fix
if any is bad.
3.2.4Power on, check voltage at pin10 of U401 if no voltage, check and fix Vertical circuit B+,
D904.
3.3No Display (No Raster).
3.3.1Check yoke connection.
3.3.2Check CRT board and verify CRT heater is on.
3.3.3Check G2 voltage if fail, check and fix FBT or D502.
3.3.4Check K (cathode) voltage at negative of D501 about 150V, If no voltage output Check and
replace D501 and C501.
3.4Vertical Deflection Failure
3.4.1Vertical display can't be held--check and fix：U401.
3.4.2 Vertical raster abnormal (one horizontal line, size too small or fold back on top / bottom) --
check and fix：14V supply at U402 pin2, if has voltage check and fix U301.
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Appendix A. Spare Parts List
Location
Parts Number
28-1100-0006
Description
Fuse, 2A/250V, slow blow
Diode 3A, 600V, RS407
Diode, 1.5A, 800V, BA159
Diode, 3A, 800V, FR107
Diode, FR1005
F901
D901
06-3100-0005
06-1100-0001
06-1100-0023
06-1100-0014
06-1100-0058
08-3100-0011
08-1100-0003
08-1100-0001
08-1100-0002
08-1100-0081
09-4100-0007
09-4100-0119
09-4100-0087
11-0100-0054
41-2100-4009
11-2100-0095
01-3203-223J
01-01 2-*39J
01-2003-823J
D902
D501, D502
D903, D904, D301
D906, D401
Diode, 2A, 600V, FR205
Power MOS 2SK2996
Transistor NPN 2SC1815
Transistor NPN 2SC2688
Transistor PNP 2SA1015
Transistor NPN 2SD667
IC TDA2579B
Q901
Q201, Q202, Q206, Q402, Q501
Q205
Q502
Q203, Q204
U401
U301
U901
FBT
IC TEA8172
IC UC3842
Flyback Transformer
Driver Transformer
Driver Transformer
CR 22K 3W
T401
T901
R902
R904
CF 0.39 1W
R614
MOF 82K 3W
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Appendix B. Schematics and PCB Layout Diagram
1. Schematics Page 1 -- Main Board, Video Board.
2. Schematics Page 2 – Power Supply, Video Amplifier
3. PCB Layout -- Video Board, Circuit Trace
4. PCB Layout -- Main Board, Silk Screen
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G 4
G 2
7
6
5
G 1
1
D
S
V C
C / t R t
7
5
4
8
G N D
f e V r
3
2
1
C 2 0 4 1 / 6 V 1 0 U
R 2 1 1 3 K 3 .
R 2 0 9 1 2 0
C 1 2 8 S 1 5
2 0 Q 3
5 / 0 V 2 U 2 .
C 2 0 5
1 0
1 1
1 2
1 3
1 4
1 5
1 6
1 7
1 8
9
8
7
6
5
4
3
2
1
8 1 . W
R 3 0 6
C 4 1 5 0 . 1
3
8
6
4
2
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