Dynamic Focus Circuit Function And Description - Ceronix 1493 Service Manual

DYNAMIC FOCUS CIRCUIT FUNCTION AND CIRCUIT DESCRIPTION.
Model 1793-31.5DF
Horizontal Drive
Transformer
CPT1505
2
332
1
12-18VDC Vs
50Vpp 29,F6
YC1
426
1,000uF
35V
YC2
+
427
449
13-15VDC Vs
3-5Vpp 31,F5
0VDC Vs
1.6Vpp
.33uF
500
0Ω
1.2Ω, 1W
502
385
The dual focus CRTs require a waveform on the #2 focus grid. This voltage waveform is dependent on the
position of the beam on the CRT. The lowest voltage part of the waveform is in the center of the screen and the
highest voltage part of the waveform is at the corners of the screen.
The dynamic focus circuit produces a composite waveform which consists of the horizontal parabolic waveform
and the vertical parabolic waveform. This composite waveform is applied to the dynamic focus input, of the
flyback transformer, and produces a sharp picture on the dual focus picture tubes. Typically dual focus picture
tubes produces a sharper picture than the single focus picture tubes.
Dynamic Focus Circuit Operation: The vertical component of the dynamic focus circuit is derived by
amplifying the voltage waveform across the vertical yoke coupling capacitor. The horizontal component of the
dynamic to focus circuit is produced by applying the voltage waveform across the horizontal yoke coupling
capacitor to the dynamic focus transformer primary. This transformer steps up the horizontal parabolic
voltage from about 33V to about 300V to produce the horizontal component of the dynamic focus circuit.
Circuit Description: Transistor
. This waveform is coupled to the transistor base via capacitor
449 449
transistor is generated by resistors
Note; Resister is connected to the vertical feed back line and not to ground. The supply voltage for the
505 505
collector is produced by diode
The load resisters for this transistor are resistors
vertical parabolic waveform, is conducted through resister
focus input of the flyback transformer. Resisters
horizontal component of the dynamic focus waveform is produced by coupling the primary of the dynamic focus
transformer at to the horizontal yoke coupling capacitors at
518 518
impedance pass to ground for the horizontal parabolic waveform which is developed across the dynamic focus
transformer secondary at
transformer primary. Resister
The flyback transformer
86
NO DVM Hs
.8KVp-p 27,G6
433
3
0Ω
1N4007 V+
4
435
452
1.2Ω
H PLL
434
DM Drive
GND
OVP
P/S Sync
VERTICAL
DEFLECTION
V-
YOKE
V+
2.2MΩ
Vs
1.00MΩ
504
2SC3467
1KΩ
509
501
191K 36K
503 505
amplifies the vertical parabolic waveform which exists across capacitor
509 509
and
503 504
503 504
which rectifiers the primary flyback pulse and is integrated by capacitor
512 512
. Capacitor
518 518 517 517
protects the dynamic focus transformer primary from overload.
516 516
couples the dynamic focus waveform to the #2 focus grid via an internal capacitor.
453
453
FLYBACK
TRANSFORMER
10
1/2W, CC
13
FOCUS
9
#2 FOCUS
SCREEN
8
12
11
7
4
5
3
2
1
CPT1555
453
2,200pF
1N4007
1KV
2.2MΩ
507
510 511
CPT1556
200KΩ
1
514
4
518
330pF
500V
515
GND
500 500
. The gain of this amplifier is defined by resister and
and . The waveform on the collector, which is the
510 511
510 511
and through transformer
514
514
and provides arc protection for transistor
514 514 501 501
and
443
443
insures that there is no D. C. component across the
EHT
470Ω
520
Dynamic Focus
0Ω
465
Beam Current
Filament
Vs
GND
HORIZONTAL YOKE
512
2
Horizontal
Linearity &
0.1uF
Width coils.
3
250V
270Ω
.47uF
516
517
Hs
443
Horizontal Width Control.
(Diode Modulator)
and resister . The bias for this
501 501
518 518
. Capacitor
444 515
444 515
CRT
.47uF .01uF
200V
1.6KV
444 441
.
505 505
.
507 507
to the dynamic
. The
509 509
provides a low