Philips FIMI FC 16N User manual

AN
V18754
.
SERVICE MANUAL
FIMI
HIGH RESOLUTION GRAPHICS MONITOR
FC 16N/FC 20N
BAUGLEICH: PHILIPS C16-N / C20-N
Schaltungsdienst Lange OHG
D-12277 Berlin
Tel.:[phone]

Technical
Operations
Manual
Philips
High
Resolution
Graphics
Monitors
Models
C16-N
and
C20-N

Table of Contents
Part I: Monitor Operations
1
Monitor
Overview
...cccccccosncscsessceserescnsssssssessssensesseesceseessssesecensssnscnsseosssseeee
Lod
1.1
Block
Diagram..........sccssssssssecsssssssssenssenscnssnonecssensasencocsnsssensaseosenseses
1-1
1.2
Monitor
Specifications
........sscssscsssspsessscssscnssnsenssssenseessenensenssenecences
1-3
2
Power
Supply
&
Degauss
Circuitry
......cc.sccnsssssnsecsnsscsssssnesssnscensosensveseee
S71
2.1
Power
Supply
.........sccoscscsssorsrssessessecessnssssenssessncsssncsssnssssncersneesnssnesess
2-1
2.2
CHOPPED
......snssccsscsscscecsssceserssesesessnessnsssanessnecensssessnnsnsseucssnesasecusenseanes
2-3
2.3
Degaussing
Circuit
......ccsscsscssrssssenssnssseseneseossscecsncsnssesseesens
sapnruren
2-6
3
Deflection
Board
.......c.scsscccecscsssesseessnssnssssssssessesssessessnscnssvesseseesensenssnesensee
J”
3.1
Horizontal
Deflection
...........sssscssssssssesscsscssscsescsenenensncnsenecscsssnsensess
3-1
3.2
ET
Stabilization
Circiiit
.........ssccscsssscscrsssssescsssrsesercerssenssnenonses
wee
7D
3.3
Vertical
Deflection
...........cssssscssssscssssssscsecsssesessensasenerensseeensecsnserseees
3-4
3.4
Auxiliary
Services
......scssscscsssssessnesesssnsssnsssnsensenssssonssossssseceneeanerneees
3-4
4
Video
Preamplifier
Board
......ssscssssssssssrsssenesenesssenssessncenssnsensensssecsosenees
4-1
4.1
Video
Preamplifiers..........scscsersssecsecseees
wuic
bia
sundae
Gatpesasispaanunisats
4-1
4.2
Synchronization
........csssscessersssessscssenceeesnssersnssencssstensarensnssernenssnsencnssees
4-2
5
Video
Output
Stages
(Socket
Board)
.......rcccsssscssecssscsecsssssnenscsesseseoneneee
5-1
5.1
Fimal
Video
Stage
.......s.sscsssssssssssscerecssssssessnsesensnenssecececsescescssanesrensnese
5-1
5.2
Black
Level
Adjustment
and
Individual
Beam
Limiting.............
5-1
5.3.
Flashover
Protection
.........0+s+0
svoscecaeananencnnennennsenncssnssssnnnnnneneecngte
5-1
6
Dynamic
Focus
Board
....-.-.serscsssscscssesccssereencencsessceresees
wee
21
Part
II:
Adjustment
Procedures
7
Equipment
Needed
for
Adjustments
.......cccessocsrsscsrssesesesenesnencanensenseoes
7-1
S
Synchromization
.........ccscscssrssenesecsceressovsresssserssqnenenensevassesensnsssssenansevecsorese
8-1
Q
EHT
Stabilization
.........cscssscscscssrsccsesnccerssensssserscsncensensosconsonsscsensccseesnsonses
9-1
10
Geometry
......ccsccccscccsseseresnseseneseessrnssserenssosssenesessessoeseesesneacansesacaesnsnssoooeees
10-1
11
Chromaticity
..........ccccscsecccscerssererecesersonosonsncoessssenessssesecnsecsssrecesssonsnononeaes
11-1
12
Focus
NOE
ATT
ST
ARAN
LE
RN
ICES
ETE
ETON
TOE
13
Troubleshooting
.....cc..csecccsssssseeccsssossssssssesersseseesssnesenssssnsecnsssanessnscseeseseseee
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1
13.1
OWOTVIEW
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13-1
13D
TMGICATOTS
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ewes
tnnedanseedchishadesnesennnsaesoutered
13-1
Appendix
A:
Monitor
Diagrams
.......s--ssesssssessnssressenensssersenensseenenrensansnssosecsenses
A-1
Appendix
B:
Layout
Diagrams...
sinbstheatedsnsiaaaustaabeaiebennesteneeseiovcctabasectatarensuene
B-1

Preface
This
Technical
Operations
Manual
is
divided
into
three
major
parts:
e
PartI-
Monitor
Operations
e
Part
II
-
Adjustment
Procedures
e
Appendix
Part
I,
Chapters
1-6,
describes
the
major
components
of
the
monitor,
includ-
ing
a
monitor
overview
and
circuit
descriptions
for
each
of
the
major
com-
ponent
blocks.
Part
I,
Chapters
7-13,
provides
instructions
for
adjusting
the
monitor’s
con-
trols
and
includes
a
chapter
on
troubleshooting.
Appendix
A
presents
a
series
of
diagrams
describing
monitor
dimensions,
control
locations,
and
how
to
access
and
replace
monitor
component
boards.
epee
B
contains
layout
diagrams
for
the
monitor’s
five
component
boards.
Inserted
in
the
back
of
the
manual
is
a
monitor
circuit
diagram
which
is
referenced
throughout
the
document.

Table of Figures
MO mitor Block Dig or ares ccsesisicsccsuszvinsschanseccssesesassnssntesscccnaincnveooweves 1-2
Power Supply & Degauss Circuitry | Block Diagram ..........s00s00 2-2
Chopper Block Diagram ..........ssscscecssscscssesssossssssscessesesncecssscesceres 2-4
Deflection Board Circuit Diagram ..........sscssscssssscsssscssecscsceenseteeces 2-5
EHT Stabilization Circuit Diagram ...........sssscssssscsssssccsnsereseeceesese 3-3
Dynamic Focus Board Circuit Diagram ........ssssessseccsseseesseressees O° 1
Appendix A: Monitor Diagrams
A-1
A-2
A-3
A-4
A-5
A-6
A-7
A-8
A-9
A-10
A-11
A-12
Appendix B: Layout Diagrams
Monitor Mechanical Dimensions C16-N .......ssssscesscsssssssseesseseees A-1
Monitor Mechanical Dimensions C20-N .........ssscsccssssecececaseesees A-2
Removing the Pedestal CIG-N | ss.ccscocsosnseesssosscntoesessonbeciseseccencovsesoe A-3
Removing the Back Cover C16-N ......sssssssssssssssssssssssesesesererecseenees A-4
Removing the Back Cover C20-N ......esssscsssssssssscssosenecssececeeesoeseses A-5
Removing the Top Metal Cover C16-N & C20-N ou... esssesseeseee A-6
Top Accessible Controls C16-N & C20-N .....e.sssssscessceseescecsceenees A-7
Side and Back Controls C16-N & C20-N ....sececssssssseesscesseesseeseeees A-8
Replacing the Power Supply C16-N & C20-N ou... ssssssecsseccscesoeees A-9
Replacing the Video Preamplifier Board C16-N & C20-N ....A-10
Replacing the CRT Socket Board C16-N & C20-N ......eeseseeees A-11
Replacing the Deflection Board C16-N & C20-N .......ssesssoees A-12
Power Supply
Chopper Board
Deflection Board
Video Preamplifier Board
Socket Board
Insert: Monitor Circuit Diagram

1 Monitor Overview
The
C16-N
and
C20-N
are
high
resolution
color
monitors
specifically
designed
for
CAD/CAM
applications
to
display
graphic
and
alphanumeric
information
with
a
resolution
of
up
to
1280
x
1024
pixels.
The
monitors
are
in
a
plastic
cabinet
with
a
tilt/swivel
base.
1.1 Block Diagram
The
block
diagram
of
the
monitor
is
shown
in
Figure
1-1.
The
electronic
circuits
are
divided
among
the
following
blocks:
°- POWER SUPPLY and DEGAUSS CIRCUITRY
° DEFLECTION BOARD
e VIDEO PREAMPLIFIER BOARD
* CRTSOCKET BOARD
e DYNAMIC FOCUS BOARD (only for C20-N)
Each
of
the
blocks
are
described
in
Chapters
2
through
Chapter
6.

CONTROL DYNAMIC FOCUS
BOARD BOARD
(ONLY FOR C20M)
Figure
1-1.
Monitor
Block
Diagram
Boao
a
a
te
ee
1-2

1.2 Monitor Specifications
Refer
to
Appendix
A
for
dimensional
diagrams
for
the
C16-N
and
C20-N
monitors.
1.2.1 Picture Tube
M48KDB56 X 40 (20")
M38JFIJ37 X 31 (16")
e 16" and 20" high resolution color tube coil assembly
90° deflection angle
0.28
(16")
and
0.31
(20")
trio
dot
pitch
29 mm neck diameter
P22 phosphor, medium-short persistance
CIE
chromaticity
coordinates:
X;=0.618
Xg=0.280
Xp
=0.152
Yr=0.350
Yg=0.605
Yb
=
0.063
white
coordinates:
X=0.281
+/-
0.02
Y
=0.311
+/-
0.02
White
coordinates
are
measured
at
the
center
of
the
CRT
face
on
a
white
window
equal
to
25%
of
total
picture.
The
contrast
control
is
set
to
30
FL.
:
The
brightness
control
is
set
to
the
threshold
of
raster
extinction.
e Brightness
1.
Normal
intensity
mode:
30-35
FL
at
0.7Vpp
video
input
signal.
Brightness
is
measured
at
the
center
of
the
CRT
face
ona
white
window
equal
to
25%
of
total
picture
with
the
contrast
control
set
to
maximum
and
brightness
control
set
to
the
threshold
of
raster
extinction.
2.
Uniformity:
Maximum
variation
from
center
to
edge
is
<
or
=
40%
(monotonic).
Brightness
is
measured
on
a
full
white
page
with
brightness
control
set
to
the
threshold
of
raster
extinction
and
the
contrast
control
set
at
20
FL
at
the
screen’s
center.
Misconvergence: 0.15 in the center
0.35mm
within
a
circle
diameter
equal
to
the
image
height
0.45mm
in
the
corners
Color
purity:
No
color
impurity
for
each
of
the
R,G,B
colors
ae
ee
ae
ce
Re
ee
oe
ee
a
1-3

1-4
12.2 Deflection
Horizontal
Frequency
range:
48
to
64
kHz
Blanking
time:
>3.5
usec
>
Retrace
time:
2.8
usec
Vertical
Frequency
range:
50
to
120
Hz
Blanking time: 39 lines
Retrace
time:
550
usec
Synchronization
Composite
sync
on
green
(0.3Vpp)
75 ohm input impedance
Geometry
With
nominal
video
inputs
pincushion
barrel
trapezium
shall
fall
within
a
3mm
band
formed
by
two
concentric
rectangles.
Linearity
Difference
between
displayed
character
sizes:
a. worst case - Ey= 10%
b.
between
adjacent
characters
-
Ey=5%
[Ey
=
(max
size
-
min
size
/
max
size)
x
100]
|
Jitter, hum: not visible
1.2.3 Video
RGB
inputs:
75
ohm,
analog
with
sync
on
green
amplitudes:
video
pulse:
min
0.65V
-
max
0.75V
-
typical
0.7V
sync
pulse:
min
0.27V-
max
0.33V
-
typical
0.3V
Resolution:
up
to
1280
x
1024
Bandwidth:
110
MHz
(at
-3dB)
linear
Rise
and
fall
times:
<
or
=
5
nsec
Overshoot: max 8%

1.2.4 Power Supply
e
AC
input
Range
A
92-132V
Range
B
184-264V
Range
select
accessible
by
the
user
e
Mains
frequency:
47/63
Hz
e
Switching
frequency:
43
Hz
+/-2
Hz
e
In-rush
current
limitation:
50A/2
usec
e Max. consumption: 120W
1.2.5 Controls
e External:
Brightness,
Contrast,
Manual
Degauss,
and
Power
On/Off
e Internal:
H-PH:
Horizontal
Phase
V-Hold:
Vertical
Frequency
Height: Vertical Size
V-Cent:
Vertical
Shift
S-Pin:
East/West
Pincushion
V-Lin:
Vertical
Linearity
Width:
Horizontal
Size
4
H-Lin:
Horizontal
Linearity
H-Cent:
Horizontal
Shift
Serv:
Service
Switch
(collapsing
Vertical
Deflection)
Trap:
Trapezoidal
Corrections
1.2.6 Input Connectors
e Signals: BNC (75 ohm)
e AC power: CEE 22-6A
1.2.7 Safety
e
UL,CSA,
DHHS,
VDE,
PTB,
TUV
approved
1.2.8 EMI/RFI
e VDE0871/6.78 class B approved
FCC-15J
class
B
(approved
on
Philips
system)
1 5

1.2.9
Reliability
e
MTBF:
more
th
25°C
an
25,000
hours
(including
CRT)
as
per
MIL-HDBK
217D
at
1.2.10
Environmental
Conditions
e
Operating
ambient
temperature:
0°C
to
+40°C
Storage
temperature:
40°C
to
+
65°C
Humidity:
5%
to
90%
RH
(non-condensing)
1-6

2
Power
Supply
and
Degaussing
Circuitry
This
chapter
describes
the
circuitry
of
the
Power
Supply
and
the
Degauss
Coil.
Figure
2-1
presents
a
simplified
block
diagram
of
these
components.
2.1 Power Supply
The
power
supply
works
at
a
fixed
frequency
of
about
43
KHz
in
flyback
mode.
The
mains
voltage,
rectified
(R1)
and
filtered
(F1),
is
applied
to
the
power
transformer
(T1)
which,
by
the
switching
power
transistor
(Q1),
transfers
the
voltages
and
the
energy
necessary
for
proper
operation
to
the
secondary
side.
The
mains
voltage
range
is
selected
by
an
external
voltage
selector
slide
switch.
In
the
110V
range,
the
bridge
rectifier
acts
as
a
doubler
circuit,
and
in
the
220V
range,
the
bridge
rectifier
acts
as
a
normal
rectifier
circuit.
An
auxiliary
voltage
(Vaux)
is
also
obtained
from
the
primary
side
of
the
transformer
which
supplies
the
Pulse
Width
Modulator
(PWM)
circuits
(based
on
the
TDA
1060
IC),
the
driver
stage,
and
the
automatic-manual
degaussing
circuitry.
During
startup
of
the
power
supply,
the
auxiliary
volt-
age
is
not
present,
and
the
voltage
necessary
for
the
PWM
is
derived
directly
from
the
rectified
mains.
The
startup
time
is
determined
by
an
R-C
network;
the
power
supply
can
only
be
restarted
after
the
R-C
network
has
been
discharged.
7
On
the
secondary
side
of
the
power
transformer,
the
square
waveforms
are
rectified
and
filtered
(RF2,
RF3),
providing
the
following
output
voltages:
+
64.5
V,
+30V,
+14.5V
and
+6V.
The
+64.5V
output
is
sensed
and
subtracted
from
a
stabilized
reference
voltage.
The
error
signal
is
amplified
and
sent
to
the
PWM
circuit
via
an
opto-coupler,
where
it
is
compared
to
a
triangular
waveform
at
fixed
fre-
quency.
The
resulting
square
waveform
modulates
the
duty
cycle
in
propor-
tion
to
the
error
signal
in
order
to
keep
the
output
voltage
constant
at
+
64.5V
against
mains
voltage
and
load
variations.
This
square
waveform
is
then
amplified
by
the
driver
stage
(transistor
Q2
and
driver
transformer
T2)
and
is
applied
to
the
power
transistor
T1,
thereby
closing
the
feedback
loop.
There
are
two
protection
thresholds.
The
primary
current
is
sensed
by
resis-
tor
RS.
If
the
first
protection
threshold
is
exceeded,
the
duty
cycle
is
con-
tained
(thus
limiting
the
output
power).
If
the
current
increases
even
further
and
surpasses
the
second
threshold,
the
power
supply
is
switched
off.
If
the
higher
output
voltages
(+
64.5V
and
+30V)
are
short-circuited,
the
primary
current
increases
causing
the
power
supply
to
be
switched
off.

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Figure 2-1. Power Supply and Degauss Circuitry Block Dia
2-2

If the lower output voltages (+ 14.5 V and +6V) are short-circuited, the
primary current does not reach the turn-off threshold due to the lower
power;
for
this
reason,
these
outputs
are
short-circuit
protected
by
a
fuse.
(An
LED
after
the
fuse
indicates
if
the
voltage
is
available
on
the
output.)
In
series
with
the
+6V
output,
the
resistor
produces
negative
current
feed-
back
in
order
to
limit
current
variation.
An OVP circuit in the classic crowbar configuration senses the 30V and
+ 14.5V output voltages. The +30V output voltage is short-circuited by an
SCR whenever the sensed voltage exceeds + 17.5V.
2.2 Chopper
Figure 2-2 presents a simplified chopper block diagram, and Figure 2-3 is a
circuit diagram of the chopper.
A chopper circuit is mounted on the power supply and provides an output
voltage which can be adjusted by a multi-turn trimmer from 76.5V to 102V.
The horizontal deflection stage needs an input voltage proportional to the
line frequency. In this way, a single power supply unit can be used for the
whole family of monitors from 48 to 64 KHz.
The chopper contains a boost switching regulator working at a fixed frequen-
cy of about 75KHz, a power inductor L, a power mosfet Q, a rectifier diode
D, an output filter F, and a PWM. The +64.5Vdc input voltage comes from
the power supply.
When the mosfet is turned on, the input voltage is applied across the power
inductor, which stores the energy.
When the mosfet is turned off, the energy stored in the inductor creates a
voltage which switches on the diode and transfers the energy to the output
filter and then to the load. Additional energy is also transferred from the
input directly to the output during the diode conduction time.
The +64.5V input voltage is applied to the PWM circuitry (based on IC
UC3842) via the resistor R.
The output voltage is sensed and is sent to the PWM where it is subtracted
from a stabilized reference voltage.
The duty cycle of the PWM square waveform is modulated in porportion to
the error signal and current amplitude in order to keep the output voltage
constant against input voltage and load variations.
This square waveform drives the power mosfet, thus closing the feedback _
loop. When a short circuit occurs at the output, the input supply voltage is
overloaded and the power supply is switched off.

&
gy
ACOV+/AG
‘9L+
(2-eEeon)
AYULINOYID
WMd
Figure
2-2.
Chopper
Block
Diagram
2-4

AZzOt/SLe
ex
OSS
-82AA8
Figure
2-3.
Chopper
Circuit
Dia
2-5

2.3
Degaussing
Circuit
The
automatic
and
manual
degaussing
circuitry
supplies
current
(via
the
PTC)
to
the
degaussing
coils
mounted
on
the
CRT
for
about
ten
seconds.
The
current
supply
is
limited
to
ten
seconds
in
order
to
allow
the
PTC
to
cool
off
again
and
to
remove
the
small
residual
demagnetizing
current
which
could
affect
spot
landing.
After
approximately
five
minutes,
the
external
manual
degaussing
controls
can
be
used
again.
The
degaussing
circuitry
consists
of
an
R-C
network,
a
comparator,
an
opto-
coupled
triac
driver
and
a
triac,
which
connects
the
selected
PTC
to
the
mains.
The
R-C
circuit
determines
the
on-time
of
the
triac.
Upon
startup,
the
comparator
drives
the
triac
via
the
opto-coupler.
When
the
R-C
network
reaches
its
trip
point,
the
comparator
inhibits
the
opto-
coupler
from
driving
the
triac.
If
the
PTC
is
cold,
the
unit
can
be
degaussed
by
simply
discharging
the
R-C
network
with
an
external
pushbutton.

3
Deflection
Board
The
deflection
board
contains
the
following
circuits:
e
Horizontal
Deflection
with
EHT
Generation
e
ENT
Stabilization
Circuit
e
Vertical
Deflection
Refer
to
the
Monitor
Circuit
Diagram
included
with
this
manual.
3.1
Horizontal
Deflection
3.1.1
Horizontal
Driver
And
Output
Stage
The
horizontal
or
composite
synchronization
signal
coming
from
the
video
preamplifier
board
is
applied
to
pin
11
of
IC
Ui
(TDA
2595/V
a
The
local
horizontal
oscillator
in
IC
U1
is
locked
by
the
input
synchroniza-
tion
signal.
There
are
two
phase
loops.
The
first
phase
loop
compares
the
phase
between
the
synchronization
pulse
and
the
oscillator.
The
range
of
this
phase
comparator
is
limited
in
order
to
prevent
damage
to
the
deflection
circuitry
at
synchronization
frequencies
beyond
the
acceptable
range.
The
second
phase
loop
compares
the
phase
between
the
oscillator
and
the
horizontal
flyback
pulse
which
is
derived
from
pin
7
of
the
line
output
trans-
former
and
applied
to
pin
2
of
the
IC
U1.
This
loop
compensates
for
storage
time
variations
in
the
horizontal
deflection
transistor
V5.
Resistor
R13
will
pull
pin
4
of
U1
high
when
transistor
V4
does
not
conduct.
When
driver
transistor
V4
conducts,
a
primary
current
will
flow
through
the
driver
transformer
T1.
The
secondary
winding
on
this
transformer
supplies
a
negative
base
current
to
the
output
transistor,
V5.
The
base
storage
charge
is
first
removed
by
this
negative
current,
after
which,
the
output
transistor
actually
ceases
to
con-
duct.
The
slope
of
this
negative
current
is
determined
by
the
leakage
induc-
tance
of
the
driver
transformer
and
the
negative
drive
voltage,
which
is
the
sum
of
the
transformer
drive
voltage
and
the
voltage
across
the
base
capacitor
C24.
After
the
storage
time,
the
base
emitter
voltage
is
driven
into
negative
breakdown.
During
this
time,
called
the
zenering
time,
the
collec-
tor
and
the
base
current
decrease
to
zero
and
turn-off
is
complete.
As
soon
as
pin
4
of
U1
is
pulled
low,
the
base
voltage
of
V4
will
fall
below
the
emitter
voltage
and
V4
will
be
switched
off.
When
the
primary
current
in
T1
is
interrupted,
the
magnetizing
current
in
the
secondary
winding
ap-
pears
as
an
almost
constant
positive
base
current
and
V5
is
turned
on.
ne
wT
3-1

3-2
R21
prevents
undesired
conduction
of
V5
caused
by
ringing
in
the
driver
stage.
C17
is
a speed-up
capacitor.
The
V4
collector
peak
voltage
is
limited
by
the
damping
network
R18
and
C18.
The
supply
voltage
for
the
horizontal
scan
is
derived
from
the
power
supply
and
is
connected
to
the
line
output
transformer
TS
at
pin
6.
3.1.2 Diode Modulator
The diode modulator has two functions:
e horizontal amplitude adjustment
e east/west pincushion and keystone correction
3.1.2.1
Horizontal
Amplitude
Adjustment
|
Since
the
average
voltage
across
a
coil
has
to
be
OV,
the
sum
of
the
voltages
across
C29
(S-correction
capacitor)
and
C32
(modulator
filter
capacitor)
has
to
be
equal
to
the
supply
voltage.
The
width
adjustment,
pincushion
and
keystone
correction
circuits
vary
the
voltage
across
C32,
which
in
turn
causes
an
identical
and
inverted
variation
on
C29,
equivalent
to
the
scan
voltage
for
the
horizontal
deflection
coil.
This
means
that
a
DC
variation
on
C24
will
result
in
a
different
supply
volt-
age
oA
re
horizontal
deflection
coils
and
therefore
will
affect
the
horizontal
amplitude.
The
advantage
of
this
type
of
modulator
is
that
the
EHT
is
independent
of
the
horizontal
amplitude.
3.1.2.2
East/West
Pincushion
Correction
The
east/west
pincushion
correction
is
needed
to
obtain
straight
left
and
right
sides
of
the
picture.
The
required
shape
of
this
correction
signal
is
a
parabola
which
is
created
by
integrating
the
vertical
sawtooth
signal
(as
avail-
able
on
resistors
R92-R93--see
vertical
deflection
stage,
Section
3.3).
The
sawtooth
voltage
is
applied
to
a
circuit
built
around
a
QUAD
OP-AMP
(U3
-
LM324)
which
generates
the
waveforms
for
east/west
pincushion
(R110)
and
keystone
correction
(R123);
these
waveforms
are
then
applied
via
the
power
transistor
V51
to
C32
for
proper
horizontal
correction.
This
signal
is
sent
to
capacitor
C32
which
is
the
same
capacitor
to
which
the
amplitude
DC-voltage
is
applied.
In
this
way,
a
parabola-shaped
deflection
current
waveform
is
obtained
without
modulating
the
EHT.

3.2,
EHT
Stabilization
Circuit
e
Because
of
the
internal
impedance
of
the
EHT
transformer,
the
size
of
the
displayed
picture
varies
with
brightness.
For
good
picture
stability,
as
re-
quired
in
a
high
resolution
monitor,
an
EHT
stabilization
circuit
is
incor-
porated.
A
block
diagram
of
the
EHT
Stabilization
circuit
is
shown
in
Figure
3-1.
An
error
amplifier
compares
a
fraction
of
the
EHT
voltage,
derived
from
a
voltage
divider
(bleeder
resistor
inside
EHT
eoaanen)
with
an
adjustable
reference
voltage
(R52)
and
generates
a
variable
supply
voltage
for
the
power
stage.
The
power
stage
is
a
resonant
flyback
converter
(V19,
V21,
C36,
T4)
which
generates
a
correction
voltage
between
0
and
2.000
Vde
which
in
turn
is
ap-
plied
to
the
bottom
of
the
EHT
winding.
|
| EMT
|
WINDING
|
|
Phe
oe
ERROR
2
7
AMPLIFIER
POWER
STAGE
am
REFERENCE
yOOT
Bes
VOLTAGE
CORRECTION
VOLTAGE
Figure
3-1.
EHT
Stabilization
Circuit
Diagram