Taxan Ergovision 740 LR User manual

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Document Title: Ergovision 740 LR & 740 TCO Service Manual
001
Nigel Inkson
issue Number:
Issued By:
Revisions:
001 Original Issue 22/05/96
Document
Control
Date of Issue: 22/05/96

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bbvssrene
ie Safety Standards and Approvals
This
monitor
complies
with
DHHS
Rules
21
CFR
Subchapter
J
Applicable
at
date
of
manufacture.
Certified
to
comply
with
che
limits
for
a
Class
B
computing
device
pursuant
to
part
15
of
FCC
rules
Please
refer
to
instructio~s
included
FCC
notice
in
the
user’s
manual
if
this
equipment
is
suspected
of
causing
interference
tc
radio
reception.
Important Safety Notice
This
equipment
conizins
special
components
which
are
important
for
safety.
These
critical
parts
should
only
be
replaced
with
the
parts
specified
by
the
manufacturer
in
order
to
prevent
X-radiation,
shock,
fire
or
other
hazards.
Do
not
modify
the
orginal
design.

Mi Preface
i Before You Start
General Safety Precautions
1. Use an isolation transformer in the power line and AC
supply to troubleshoot.
2. When servicing, observe the original lead dress, espe-
cially in the high voltage circuits. If a short circuit is
found, replace all parts which have been overheated or
damaged.
3. Before turing the display on, measure the resistance
between B+ line and chassis ground. Connect the nega-
tive side of an ohmmeter to the B+ fines and the positive
side to chassis ground. Each line should have more
resisstance than the following specifications:
| +200V 134.5KQ |
} TV 60.51KQ
(eee ees ee ee
PER Bak
| +15V 27.13KQ |
4.1502
4. Potentials, as high as 26kV are present when this display
is in Operation. Operation of the display without the rear
cover involves the danger of a shock hazard from the
display power supply. Servicing should not be at-
tempted by anyone who is not thoroughly familiar with
the precautions necessary when working on high volt-
age equipment. Always discharge the anode of the pic-
ture tube to the display chassis before handling the tube.
5. After servicing, be sure to check the items listed in the
Safety Checkout, below before returning the serviced
unit to the customer.
Safety Checkout
The following checks must be made after correcting the
original service problem and before the unit is returned to the
customer.
1. Check the area of your repair for unsoldered or poorly
soldered connections. Check the entire board surface for
solder splashes and bridges.
2. Check the inter board wiring to ensure that no wires are
pinched or coated with high-wattage resistors.
3. Check that all control knobs, shields, covers, ground
Straps and mounting hardware have been replaced.
Makde absolutely sure you have replaced all the insula-
tors.
4, Look for any unauthorized replacement parts, particu-
larly transistors, that may have been installed dueing a
previous repair. Point them out to the customer land
recommend their replacement.
5. Look for parts which, though functioning, show obvious
signs of deterioration. Point them out to the customer
and recommend their replacement.
6. Check the line cord for cracks and abrasion. Recom-
mend the replacement of any such line cord to the
customer.
7. After making any repair, check the B+ and HV to see
whether they are at the values specified. Make sure your
instruments are accurate; if your HV meter always
shows a low HV, check the meter to ensure it is not
malfunctioning.
8. Carry out the leakage current checks as detailed below
overleaf,
Leakage Current Cold Check
1. Unplug the AC cord and connect a jumper between the
two prongs on the plug.
2. Turn on the display power switch.
3. Use an ohmmicter to measure the resistance value be-
tween the jumpered AC plug and cach exposed metallic
cabint part on the display, such as scre«heads, terminals
control shafts, etc. When an exposed metallic part has a
return path to the chassis, the reading should be between
240k and 5.2M. When exposed mets: does not have a
return path to the chassis, the reading must be.
vy
i,

Leakage Current Hot Check
1. Plug the AC cord into the AC outlet. Do not use an
isolation transformer for this check.
2. Connect a 1.5k, 10 watt resistor in parallel with a 0.15F
capacitor between each exposed metallic part on the set’
and a good earth ground (see How to Find a Good Earth,
below) as shown in the diagram below.
Leakage Current Hot-Check Circuit
AC VOLTMETER
oY
—~O o
0.15nF
=
MW
15002, 10W
To instrument's —*
exposed metal
parts
Example of Leakage Current Hot-Check Circuit
Good earth
ground
3. Use an AC voltmeter with 1000 ohms/volt or more
sensitivity to measure the potential across the resistor.
4. Check each exposed metallic part, and measure the
voltage at each point.
5. Reverse the polarity of the AC plug in the AC outlet and
repeat the above measurements.
6. The potential at any point should not exceed 0.75 volt
RMS. A leakage current tester (Simpson Model 229,
RCA WT-540A or equivalent) may be used to make the
hot checks.
Leakage current must not exceed 0.5 milliamp. Ifa measure-
ment is outside of the specified limit, there is a possibility of
a shock hazard and the monitor should be repaired and re-
checked before it is returned to the customer.
How to Find A Good Earth
A cold water pipe is a guaranteed earth ground; the cover plate
retaining screw on most AC outlet boxes is also at earth
ground. If the retaining screw is to be used as your earth
ground, verify that it is at ground by measuring the resistance
between it and a cold water pipe with an ohmmeter. The
reading should be zero (0) ohms. If a cold water pipe is not
accessible, connect a 60-100 watt trouble light (not a neon
lamp) between the hot side of an AC power receptacle and the
retaining screw. Try both slots, if necessary, to locate the hot
side of the line. The lamp should light at normal brilliance if
the screw its at ground potential
Trouble light
Mie
Ohmmeter
AC Wall Socket
Cold water pipe
How to Check for Earth Ground

Table of Contents
[Section 1)
Product Specification
1.1.Monitor Control Locations & Functions . 2... 0 ee ee ee 1-1
1:2:Product Overview. 6.6 eck a ee Re te ew Oe Ee 1-2
1:3:CRT Characteristics: «ise sok Zak de Ae OE ee SR 1-2
44. Power SpeciliGations: o.& %-%.4 a wi. cameta Ae he Ge eae eee we ewe GAS 1-2
PVA ATPOWErSUDDIV: 4. Gas GE eee Reh Be ae ee a ee Ee ew S 1-2
1.4.2.PowerManagement ... 0... 2 1-2
1.5.Video Specifications. 2 0. ee 1-2
1.5.1.Video Amplifier Performance. ........ Rade eae ba Ses eh det va a Meee a Peery Gack 1-2
1.5.2.Video Input Signal Characteristics .. 0. 0 ee ee 1-2
1.6.Syne Inpub’Signal Characteristics:«- « x-y.4.4 ste aw G hee oh ok eA ge we 1-2
Os Separate: Synce sei 2 cet neta we Ea a een Ohne aint AO ee 1-2
4: 6:2.Composite:Sync. sk sce eta wa RB a ek ee ede 1-2
16:3:;Syne-On-Greens:..4, ats. isk a ee ees PS Posed Sah eee he Ae ae ee 1-3
Te7-Environmentalis 25.4. 248 ae ee a ae ER Ae te en Ae ee ee 1-3
1.7.1.Temperature/Humidity/Altitude ....... teddies ee ates. tf oe a eas 1-3
1752 Vibration Test. sa vee ised Gea we AA oe we ene ek be ae Gee 1-3
TFS sDIOD MOS 4: ate te ok Aad va GE ee ee Ee OT a 1-3
1.8.Preset Timing Modes . 2... 1-3
[Section 2.
Disassembly Instructions
2.1.Removing the Rear Cover 2. 10. 2-1
2.2.Remove Top Shield and Rear Shield... 2... 2 ee ee 2-1
2.3.Internal Disassembly (Right Side). 2 2 2 2-1
2.4.Internal Disassembly (Left Side) . 2... ee 2-1
2.5.Removing the Neck Board & Main Board... 1... es 2-2
2.6.Remove the Control Board .. 2... 2. 2-2
[Section 3,
Theory of Operation
3.1 ySwitehing Power Supply” 4.02 4.0. 2g Aes ieee A Eb be Be a ee et 3-14
Sol WwAUtO-degauSsing: 6... ad ota aoe Sayer ae Sl be ae aes we deat ed 3-2
3.1.2.Suspend Mode Operation .. 1... 3-2
3.2.The Deflection Circuit. 2. 3-2
3.2.1.16301 LM1291 Video PLL System for Continuous-Syne. 2... ee 3-2
3.2.2.1C301 LM1291 Pin Descriptions .. 2... 2.2... ee 3-4
3.2.3.1C302 LM1295 DC Controlled Geometry Correction System 2... 2. ...02.. 3-5
3.2.4.1C302 LM1295 Pin Descriptions .. 2... ee 3-5
3.2.5.Vertical Deflection Circuit. 2. 0 2 2 ee ae ee ee ee 3-6
3.2.6.Geometry Correction Circuit 2... 3-7
3.2.7.Structure of Horizontal Deflection Circuit. 2 2 ee 3-7
3:2.8.X-RAY Protection: Citeult .205 cee ew op a we ee 3-12
S279: The FOCus Circuit oa sye, oe ier Bel a eS OH ad ee he Sd A 3-12
EV740LR Service Manual Table of Contents / 1

3.2.10.Horizontal linearity and CS Switching | .
3.3.Video Amplifier... 2... 002,
3.4.Microprocessor And Sync Processing ...... .
Section 4
Setup Adjustments
4.1.Preparing the Display for Adjustment ... 2...
4.1.1.Test Equipment Required... 0.0.2.2...
4.2.Adjustment Procedures ........020022..,
4.2.1.Adjustment Sequence ...........,
4.2.2.Preset Timings Used During Adjustment
4.3.High Voltage Verification... .......022.
4.4.G1 Voltage Adjustment... .....000000.
4.5.Background Brightness Setting ..........
4.6.Screen Brightness Adjustment... .....020..,
4.7.Magnetic Field Configuration. .......20202..,
4.8.Raster Center Verification .......0002,
4.9.Tilt Verification 2.2.0.0... .000000000,
4.11.Color Misconvergence .............
4.12.Primary Test Mode Performance Adjustments .
4.13.Performance Adjustments for All Preset Modes
4.14.lmage Performance Verification .. 2.0.0...
4.15.Uniformity Verification. . 2...
4.16.Brightness Verification Hg) FN Ae we ae
4.17.Display Size Stability 2... 000.0000 20.,
4.18.Color Purity Verification... 2...
4.19.Video Noise... . 2... ee
4.20.Power Saving Check .........,..0.2..
4.21.DDC 1/2 Data Writing... 2...
[Section 5.
Troubleshooting
5.1.No Display at Power-on .. 2... .0.020002..,
5.2.No X-ray Operation... 2... 2...
5.3.No Video Operation ........0..00020..
5.4.Poor VerticalLinearity ..........0.00.,
5.5.Poor Horizontal Linearity... 2... 2
5.6.Poor Uniformity...
5.7.Tilted Display Area...
5.8.Misconvergence ............0.....,
5.9.Poor Regulation . 2... 00000020204,
5.10.PoorFocus ...............0. 0...
[Section 6,
Printed Circuit Boards
6.1.Neck Board... .....02.2.20,022..,
6.2.Main Board ......2.2.,20202202..,
2/ Table of Contents

6:3: Control: Board’ ss sch. acee y, ae a we Bah Soe IS al ak ae a Se 6-3
6.4.PCB Wiring Connection... 2. ee 6-3
Schematic Diagrams
7.1.Video Circuit Diagram . 6. 1 toluene 7-1
7.2.Deflection & S/P/S & Logic Circuit Diagram... 2... ee ee 7-1
Mechanical Parts
Be Key to-Exolodad Views «oce's ak: b Aes) AR a ee, © OS He Be a OR eS 8-1
6:2.Exploded VieW: 25 Lak lise dete ee ae a ee a et eed ea gS he 8-2
[Section 9!
PCB Component List
9.1.Explanation of Parts Listing... ee 9-1
9:2" Main Board: c.g 8 sara Ce acds Foc hee A ee er ee ER ae ee, ee ee te 9-1
9:9:Neck Board! 2-23 oso. Gls 8 a Rte ws ate a ee od te a A a 9-7
9:4. Control: Board. 2.3 05. eo ee. te SIS ER ey Ge oie at pe he eB We we 9-9
9.5.HITACHI CRT Different List. 2. 2 2. 9-9
9.6. TOSHIBA CRT Different List 2... 2 9-9
EV740LR Service Manual Table of Contents /3

Notes
4/
Table
of
Contents
EV740LR
Service
Manual

~
Product
Specification
Tate
Monitor
Control
Locations
and
Functions
........-
1-1
1.2.
Product
Overview
...
2...
0.
cee
eee
eens
1-2
13;
CRT
CharacteristicS
..
0...
6c
cee
eee
eee
1-2
1.4.
Power
Specifications.
0.6...
.
eee
eee
eee
eee
1-2
1.5.
Video
Specifications
....
6...
cere
eee
eee
ees
1-2
1.6.
Sync
Input
Signal
Characteristics
........-..++-.
1-2
Tet
Environmental.
......00
00
ee
eee
eee
teenies
1-3
1.8.
Preset
Timing
Modes
......-.-.
seer
tress
1-3

EV740LR Service Manual : : :
1.1. Monitor Control Locations &
Functions
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KEY TO BUILT-IN MONITOR CONTROL FUNCTIONS
Manual Degauss and
Ractery. Se ing Recall
unction
Digital
control
for
manual
degauss
of
monitor
at
the
normal
condition
and
for
recall
the
origional
factory
setting,
during
OSD
pattern
is
on
screen.
Thumbwheel for
Adjusting Setting and
OSD Function
Selection
Thumbwheel
for
adjusting
the
setting,
clockwise
for
increasing
and
counterclockwise
for
decreasing
and
selection
the
OSD
function
icon.
Push
Button
for
OSD
|
Press
to
call
up
OSD
function
into
screen
and
confirm
the
thumbwheel
ON/OFF
and
enter
for
icon.
Thumbwheel
Enter
Confirm
Increase
/
decrease
raster
black
level
using
thumbwheel
adjusting,
Brightness Control :
B
clockwise
for
increasing
and
counterclockwise
for
decreasing.
utton
Contrast Control
Butto
Increase / decrease video gain using thumbwheel adjusting, clockwise for
n
increasing and counterclockwise for decreasing.
Hard power On/Off button. Adjacent LED is lit when on. The LED color is
green for normal condition and change to orange for DPMS condition. —
Power On/Off
1-1

: Product Specification
1.2. Product Overview [] EPA energy star............. standby < 30 watts
The monitor installed in the EV740LR (RMH 7H11) phom
described in this service manual has the following features:
1.5. Video Specifications
O
17
inches
0.26mm
dot
pitch
conventional
CRT
1.5.1.
Video
Amplifier
Performance
30-85
kHz
horizontal
scanning
:
.
;
O
Bandwidth
(dot
rate).........
135MHz
O
Thirteen
preset
modes
:
:
;
;
O
Typical
10%~90%
rise
and
fall
times
calculation
5.5ns
1
Universal
segmented
auto
range
power
supply
: ;
;
;
.
O
Video
generator
rise/fall
times
.
2ns
maximum
O
VESA/NUTEK/EPA
compliant
power
management
;
O
Scope
and
probe
bandwidth
...
350MHz
minimum
41.3.
CRT
Characteristics
O
Probe
capacitance
...........
2.5Pf
:
O)
Overshoot/Undershoot
.......
10%
maximum
O
Screen
Size,............005.
17
inches
:
fC]
Sync
on
green
..............
Amphitude:714mV
O
Faceplate
Type............-.
Fs
maximum
Sync
on
Green
Amplitude:286mV
maximum
O
Orientation.............0045
Landscape
C
Phosphor
Dot
Pitch..........
0.26mm,
1.5.2.
Video
Input
Signal
Characteristics
delta
atvangement
a
:
O
Video
Type
................
Analog
Oo
aan
GUNG
edn
es,
ear
Fi
Amplitudes
ceneniucesley
ss
700mV
maximum
a
oe
etree
ae
:
cee
O
Video
Input
Impedance.......
75
Ohms+1%
cic
a
ee
1
Optional
DDC
1/2B
Video
Connector
Pin
Assign-
O
Phosphor
Type.............-
P22
fients:
CO
Phosphor
Persistence.........
Medium
Short
O
Faceplate
Properties..........
ASN
coating,
mn
on
nner
anti-static,
anti-reflection
|
pin.
Signal
|
O
Standard
Light
Transmission...
53.5%
Typical
Red
video
Bd : Sync return
1.4. Power Specifications Monitor GND
12 | SDA(bi-directional) |
1.4.1. Power Supply 13 1H. sync
O A/C Receptacle ..........-0. 1EC320 14 |V. sync (VCLK) _|
O Power Supply Type.......... Universal | 15 [SCL
O A/C Line Voltage Ranges ..... 88VAC-132VAC
180VAC-264VAC
O A/C Line Frequency Ranges ... 50Hz/60Hz+3Hz
| YOO®O®
O
Inrush
Current..............
30A/132V
or
|
©®O®O®
@
SOA/264V
(at
cold
start)
ig
Q®R
OG
O
Leakage
Current.............
<3.5mA
|
sai=s
=
O Degauss .............-. 000 Automatic and
Manual (20 minutes for a full recovery)
1.6. Sync Input Signal Characteristics
1.4.2. Power Management
Oo
Summary
of
operating
states:
1.6.1.
Separate
Sync
Automatic O Syne Type ....... 2.2 eee TTL
EE ONELY : ad
Time O Amplitude ..............0.0. 2.4V minimum
green not applicable (Logie High), 0.8V max.(Logic Low)
orange <3 seconds QO Polartly .. 0.0.0.0... ee eee Positive or Negative
orange <10 seconds (1 Equalization pulses .......... Not allowed
orange <10 seconds Shan’
; 1.6.2. Composite Sync
| green not applicable
" ; ; mot O Syne Type ...... 62... eee TTL
O Signaling compliant with VESA DPMS guidelines :
} aot O Amphtude...........0..00. 2.4V minimum
O Nutek 1992 guidelines........ suspend < 30 watts; (Logic High), 0.8V max.(Logic Low)
off < 8 watts

EV740LR Service Manual La
O Polarity ................2.. Positive or Negative
O Serration pulses............. Allowed at horizontal
rate
( Equalization pulses.......... Not allowed
1.6.3. Syne On Green
O Syne Type..............04. As per Apple
O Amplitude ................. OV min(Logic High)
-286mV max.(Logic Low)
O Polarity ................04. Negative/Composite
Ol Serration pulses............. Allowed at horizontal
rate
O Equalization pulses.......,.. Not allowed
1.7. Environmental
1.7.1. Temperature/Humidity/Altitude
OPERATING
O Temperature.......... 10°C to 35°C
O Relative Humidity ..... 0 to 90%,
non-condensation
O Altitude .............
NON-OPERATING
0 to 10,000 feet
O Temperature.......... -40°C to +65°C
‘O Relative Huntidity ..... 0 to 95%,
non-condensation
O Altitude ............. 0 to 40,000 feet
Vibration Test
UNPACKED UNIT
1.7.2.
Operating without package:
|__| Frequency |
|_i_| 5:22
| 22-500Hz
Times/Cycle:
Amplitude Acceleration(G)
O Rise Time.................. 10 Minutes
O Fall Time.................. 10 Minutes
O Number of Sweeps .......... I Cycle
EAS Soa eile aes ten tieat X,Y,Z
C Total Times ................ 60 Minutes
PACKAGED UNIT
Storage with package:
Acceleration(G) |
0.83G
Amplitude
Frequency
5-5O0Hz
Times/Cycle:
O Rise Time...........0..00., 10 Minutes
O Fall Time........0.....0... 10 Minutes
1-3
O Number of Sweeps.......... 1 Cycle
ED AXIS oes pices eons bee ke a eed X,Y,Z
O Total Times................ 60 Minutes
1.7.3. Drop Test
O Compliant with NSTA Project 1A guidelines
O Drop Height ............... 46cm
O Test Direction..............
1.8. Preset Timing Modes
This display has 13 preset display modes configured during
manufacture, given in the following table:
eDoti
1280x1024 |
1024x768
1024x768
1024x768
800x600
800x600
800x600 |
43.269 640x480 _|
| _o9 37.736 640x480 _|
640x480
640x480
| 12 31.469 640x400
31.470 640x350 _|
68.677
60.023
58.230
53.674
48.044
46.875
‘3
CINE
Be
j=) jee)
1 Corner, 3 Edges, 6 Faces

_ ss
Disassembly
Instructions
—
2A; Removing the Rear COVE sd aN Million Dawe Ota kes 6 2-1
22. Removing the Top Shield and Rear Shield........ 2-1
2.3, Internal Disassembly (Right Side)............... 2-1
2.4. Internal Disassembly (Left Side)................ 2-1
2.5. Removing the Neck Board and Main Board
2.6. Removing the Control Board................05. 2-2

3 EV740LR Service Manual ;
2.1. Removing the Rear Cover
1. Remove the four screws at the rear of the display. Refer
to the figure 2-1 (A).
2. Remove the rear cover.
Figure 2-3 Remove the Top Shield & Rear Shield
2.3. Internal Disassembly (Right Side)
The neck board is plugged on to the CRT neck and is enclosed
in a metal shielding.
1. Disconnect the two ground wires. Refer to the figure 2-4
(A).
2. Remove the connected pin from the Neck Board. Refer
to the figure 2-4 (B).
Figure
2-1
Remove
the
Rear
Cover
3.
Remove
the
two
connected
pins
from
the
Main
Board.
Refer
to
the
figure
2-4
(C).
2.2.
Remove
Top
Shield
and
Rear
_
4.
Remove
the
connected
pin
from
the
Main
Board
to
Control Board. Refer to the figure 2-4 (D).
Shield
5. Remove the two screws at the bezel. Refer to the figure
1. Disconnect the five ground wires from the top shield. 2-4 (E).
Refer to the figure 2-2 (A).
=
A)
6.
Remove
the
nylon
revets
holding
from
Bezel.
Refer
to
2.
Remove
the
two
screws
at
the
top
shield.
Refer
to
the
the
figure
2-4
(F).
figure
2-2
(B).
3. Disconnect the two ground wires from the top shield.
Refer to the figure 2-3 (A). an
ze)
a
4, Remove the two screws at the top shield. Refer to the
figure 2-3 (B). ]
5. Release the cord cramp from the top shield. Refer to the
figure 2-3 (C).
6. Remove top shield and rear shield.
Figure 2-4 Internal Disassembly (Right Side)
2.4. Internal Disassembly (Left Side) =~
1. Disconnect the ground wire. Refer to the figure 2-5 (A).
2. Remove the connected pins from the Main Board. Refer
Figure 2-2 Remove the Top Shield & Rear Shield to the figure 2-5 (B).
2-1
rs
Ss?

Disassembly Instructions
IMPORTANT NOTE
To avoid risk of electric shock, before re-
moving the anode cap, made sure tdhe an-
ode has been completely discharged as
high voltage may remain on the anode for
extended time after power off.
3. Remove the anode cap from the CRT. Refer to the figure
2-5(C).
4.
Remove
the
two
screws
at
the
bezel.
Refer
to
the
figure
2-5
(D).
5.
Remove
the
nylon
revets
holding
from
bezel.
Refer
to
the
figure
2-5
(E).
Figure 2-7 Remove the Control Boaed
Figure 2-5 Internal Disassembly (Left Side)
2.5. Removing the Neck Board &
Main Board
1. Disconnect the three ground wires from the Neck
Shield. Refer to the figure 2-6 (A).
2. Remove the neck shield.
3. Remove.the Neck Board.
4. Remove the Main Board.
2.6. Remove the Control Board
1. Remove the four screws from the Control! Board. Refer
to the figure 2-7 (A).
2. Remove the Control Board.

EV740LR
Service
Manual
Notes
2-3

3.1.
3.2.
3.3.
3.4.
Theory of Operation
Switching Power Supply
The Deflection Circuit
Video: AMDIING! «40st scan ae eat eas eee eS 3-12
Microprocessor and Sync Processing............ 3-13

EV740LR
Service
Manual
_
|
3.1. Switching Power Supply
The switching power supply (SPS) used in this display is a
150W flyback mode type. The power supply provides seven
outputs (B+, 77V, 15V, -15V, 6.3V ,415V and +5V). Please
refer to schematic diagram for details of the circuit layout. The
input voltage is from 88VAC — 264VAC with an input
frequency of 47Hz — 63Hz. as shown in figure 3-1.
The current first passes through the EMI control circuit and
is regulated to DC by the bridge diodes (BD901) and filter
capacitor (C907). During rectification a large current surge is
generated and as C907 has a very low impedance while being
charged the fuse, on/off switch and bridge diode are all liable
to be damaged. Forthis reason, a thermal resistor (NTCR) is
added before the bridge diode in order to limit the large current
surge generated during the charging of the capacitor.
During rectification, C910 is charged through R903 and
R904. When C910 is charged to 16V, IC901 3842A starts to
operate (for details, of the functions of this IC, please refer to
the relevant data sheet) and outputs a pulse signal from Pin 6
to set the transistor Q902 in the ON state. At this time,
transformer T903, which is connected in parallel, starts to
store power. When the current passing through the resistor
R914, and the supplementary current from R957 and R964
into Pin 3 of IC901 reaches 1.1V, IC9O1 is reset, causing the
energy stored by the transformer to reach the rated value. In
order to prevent the transformer from being saturated and
causing damage to the transistor, when transistor Q902 is in
the OFF state, the energy stored in the transformer T903 is
released into the secondary coil and is regulated through the
various output loops and filters and converted to the required
DC output. In addition to this, at the appropriate time, the
windings pin! — pin2 supply Pin 7 of IC9Q1 with a fixed
power supply for normal operation. Also, when windings pin2
— pin3 are in power saving active state, power is supplied to
Pin 7 of IC901 for normal operation.
In
any
of
the
above
cased,
the
output
pulse
is
terminated
and
the
FET
is
turned
off,
causing
the
voltage
on
the
output
of
the
FET
to
rise
rapidly,
and
the
voltage
across
the
winding
of
the
primary
to
reverse
in
polarity,
thus
tending
to
reset
the
flux
within
the
core.
At
this
point,
the
diodes
D915,
D925,
D917-
D920
and
D926
on
the
secondary
supply
winding
become
forward
biased
and
begin
to
conduct,
thus
transferring
energy
from
primary
to
the
secondary,
and
charging
the
secondary
capacitors.
There
is
also
secondary
winding
the
primary
side
of
the
power
supply
which,
through
diode
D908
and
Q901
recharges
the
control
IC901
reservoir
capacitor
C910.
This
supply
then
keeps
the
IC901
running.
In
the
event
of
a
secondary
short
circuit,
the
supply
fails
to
recharge,
thus
the
voltage
across
C910
drops
to
a
threshold
limit
below
which
the
[C901
cuts
out
and
returns
to
its
low
current
load
operation.
During
normal
operation,
the
supply
rails
charge
until
the
error
amplifier
realized
by
IC903
on
the
secondary
begins
to
turn
on
the
opto-coupler,
PH901.
At
this
point,
the
photo-tran-
sistor
of
this
opto-coupler
on
the
primary
side
begins
to
conduct,
draining
current
from
the
primary
control
IC901
supply
through
diode
D907
and
D928.
Under
normal
operation
IC903
regulates
the
current
flow
through
PH901,
and
hence
determines
the
output
voltage
of
the
error
amplifier
internal
to
IC901.
Various
passive
compo-
nents
around
[C903
and
IC901
set
the
gain
compensation
for
optimum
stability
and
regulation
characteristics.
In
the
event
of
a
fault
condition
occurring,
either
Q904
may
be
turned
on
by
the
lack
of
voltage
at
pin2
of
IC901
or
zener
diode
ZD903
may
conduct,
due
to
excessive
voltage
on
the
primary
IC901
supply.
In
the
latter
case,
the
triac
Q903
will
fire,
thus
dragging
down
the
output
of
the
control
IC901
error
amplifier,
which
in
turn
will
limit
the
duty
cycle
and
reduce
the
output
voltage.
It
will
stay
in
this
mode
until
the
AC
input
power
is
removed.
PMG1CONTROL |.
FROM LOGIC CIRCUIT PMG1——— CIRCUIT Q905
weasel
ISOLATION FEEDBACK
prea Moe Shoes CIRCUIT ats CIRCUIT
[ PH901 1C903
|
loss
a
Bin
tel
FROM
FBT
oe
:
PULSE
SYNC
CIRCUIT
PWM
CONTROL
CIRCUIT
|
MAIN
SWITCH
30Khz~85Khz ‘| Q907 a UC3842A (1C901) Pe _ qQg902
FUSE
Om
B5VAC~264VAC AC IVP tp Ue
EMI CIRCUIT
T902
AUTO OR MANUAL |! |
DEGAUSSING CIRCUIT |
Q91i5,RL901 ft j
FILTER CIRCUIT BD901
’ ee te PTV
I
Wid
ion.
te
eed
te?
>
15V
POWER
X'FORMER
O/P
RECTIFIER
pssy
12V
|
an
@EILTERS
eo
oeeeaesy
ae
|
———-+
CIRCUIT
|
|
NC
,
»
6.3V
ei
T903
Sy
|
»
5V
- =» B+ (200V)
Figure 3-1 Switching Power Supply Block Diagram
3-1
"e

i Theory of Operation
When the feedback signal passing through the main 77V
output is completed, the transistor's duty cycle is adjusted
through the transfer to Pin 2 of IC901 3842A of the primary
coil by PH901 4N35 and IC903 TL431, stabilizing the output
current. At this time, it is important to note that before the
feedback signal is established, the charge level of C917 cannot
trigger Q903 SCR or it will cause a faulty power startup. In
addition, in order to synchronize the supply power and moni-
tor and reduce noise that will cause interference to the display,
in the area D913 the monitor's feedback transformer gets a
feedback signal in order to ensure synchronization between
the power supply and monitor, with synchronization in the
range 30kHz — 85kHz. Because the power operating fre-
quency changes with the monitor causing changes in the value
of IP, (the value of LP is fixed while the value of IP increase
or decreases according to the frequency), this affects the test
value of Pin 3 of IC901 3842A. This causes the total power
supplied to vary according to the frequency, so a compensa-
tion value is provided by D914 in order to reduce the differ-
ence in total power for different frequencies. In addition,
because the AC input ranges from 85VAC to 264VAC, this
causes the value of the direct current on the DC bus to vary,
affecting the rise rate of IP, the oscillator and the duty cycle,
and causing the test value obtained at Pin 3 of IC9O1 to vary.
To resolve this, a compensation value is provided by R964
and R957 which reduces the difference resulting from the
different input voltages.
3.1.1. Auto-degaussing =
‘When base of Q915 connector is in high state, the
transistor Q915 2SC945P is on, causing the relay to
jump from Normal Open (N.O.) to Normal Close (N.
C.):to perform auto-degaussing operations. The du-
ration of this operation is controlled by a logic pulse
and lasts approximately 6 (six) seconds. When tran-
sistor Q915 enters the OFF state and the relay returns
to N.O. to terminate the auto-degaussing operation is
completed.
3.1.2. Suspend Mode Operation
Two feedback ratios can be selected, both sensing
from the 78V rail. In the event of Q905 being turned
on by micro processor, additional current is drawn
from the virtual earth node of IC903, thus causing the
power supply to serve the rail to a high voltage,
nominally 78V. This is trimmed by resistor R937,
R940 and R941. The other supply raif are predeter-
mined ratios of this winging, being +15V,-
12V,+6.3V and +200V nominally. In addition, a low
voltage primary side winding feeds the control IC901
directly through D907 turning off the control [C901
supply through Q901, which would otherwise dissi-
pale excessively.
When Q905 is turned off, the 78 V rail drop to around
17V. In this case, the primary control supply fed
through D907 drops to a value that is below the level
needed to sustain operation. Instead, Q901 begins to
conduct and the higher voltage supply winding taken
via
D908
is
used
to
keep
the
primary
side
powered
up
with
minimal
power
losses.
The
5V
power
supply
is
driven
by
one
of
two
sources,
In
normal
operation
when
the
78V
is
present,
the
5V_.
regulator,
IC902
is
fed
from
the
15V
rail
through
diode
D921.
When
switched
to
standby
mode
(78V
rail
drops
to
12V)
then
the
15V
rail
drops
too
low
to
supply
IC902.
In
this
case
Q906
take
over
and
main-
tains
the
supply
to
IC902
at
around
9V.
In
addition
to
the
5V
regulated
supply,
in
normal
operation
there
is
also
a
15V
regulated
supply
take
from
the
15V
rail.
To
ensure
that
micro
processor
gets
a
good
5V
power
supply,
there
is
a
power
good
detection
circuit
.
formed
by
Q801
and
Q802.
This
monitors
the
supply
going
into
the
5V
rail
(not
the
5V
rail
directly).
It
detects
whether
there
is sufficient
voltage
to
enable
the
SV
regulator
to
work
effectively.
It
is
not
a
detection
of
the
5V
rail
itself,
but
relies
upon
the
premise
that
the
regulator
is
not
faulty
and
that
there
is
no
faulty
load
condition
on
the
5V.
During power up, there is a delay to the signal at the
output of the threshold comparator Q801 and Q802
a caused by ZD801 and C801, in order to allow the
micro Circuit time to stabilize. The threshold is cho-
sen
such
that
the
RESET
line
drops
low
at
least
25ms
before the SV drop out of regulation. — L
Finally
a
synchronization
pulsé
taken
from
the’
oii
zontal
output
stage
maintains
the
SMPS
operating
frequency
in
sync
with
the
horizontal
scan.
D913
injects
a
pulse
which
prematurely
triggers
the
oscil-
lator
within
IC901
which
would
otherwise
run
at
a
frequency
lower
than
the
minimum
required
sync
frequency.
3.2. The Deflection Circuit
Please refer to the block diagram of the deflection circuit and
video circuit and Logic circuit as shown in figure 3-2.
3.2.1. IC301 LM1291 Video PLL System for Con-
tinuous-Sync
The LM [291 is an integrated horizontal time base solu-
tion specifically designed to operate in continuous-sync
video monitors. If automatically synchronizes to any H
ferquency from 30kHz to 85kHz and provides the drive
pulse to the high power deflection circuit.
Available sync processing includes a vertical sync sepa-
rator and a composite video syne stripper. An internal
syne selection scheme giyes highest priorily to separate
Hand V syne, then composite sync, and finally syne on
video, no external switching between sync sources is
necessary, The LM1291 provides polarity-normalized..*2
H/HV and V sync outputs, along with logic flags which
show the respective input polarities.
The design uses an on-chip FVC (Frequency to Voltage
Converter) to set the center frequency of the VCO
a
a
a
a
3-2

EV740LR Service Manual
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-2 Video, Logic,Audio and Deflection Block Diagram
Figure 3
3-3