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Technical Manual
The CTC 49 Color Chassis
Trans Vista 100
Technical Manual
The CTC 49 Color Chassis
Prepared By
Copyright © 1970 by RCA Sales Corporation
RCA Sales Corporation
All rights reserved. No part of the material protected by this copyright
A Subsidiary of RCA Corporation may be reproduced or utilized in any form without written permission
from copyright owner.
Product Performance--Technical Training
600 North Sherman Drive
Indianapolis, Indiana 46201
Price $4.50
First Edition 7032
Trademark(s) ,
ARegistered Marca(s) Registrada(s) Punted in U.S A.
· " "ell· - 4, 4re*
e
·
CONTENTS
General Description 1
RF and IF System 7
The Video System 15
Horizontal Deflection 27
Vertical Deflection 35
First- Level Maintenance 43
Shop- Level Maintenance 57
1
FOREWORD
The CTC 49 chassis represents the first of a " new breed" of RCA
all-solid-state color television receivers. This is particularly true from
the standpoint of servicing. The extensive use of plug-in circuit modules,
eleven in all, a tuner which may be exchanged without the need for
realignment of the coupling circuit to the IF amplifier, a solid-state
high-voltage quadrupler, which essentially is another module, and the use
of plug-in transistors makes it possible to correct most failures with
very little servicing effort.
In the preparation of this manual less than the usual space was
devoted to circuit description for three reasons. First, some of the circuitry
bears a close resemblance to earlier RCA chassis. This is true of the
tuner, AFT, and horizontal deflection system, which are similar to their
counterparts in either the CTC 40 or CTC 47 chassis; and the
sound module which is almost identical to the one used in the CTC 41, 42,
and 43 chassis. Second, integrated circuits are used in the IF and
chroma circuits, and a stage- by-stage analysis of these systems has little
value to the service technician, since many active devices are packaged
in a single unit. Third, since most repairs can be accomplished most
readily by module replacement, rather than by replacement of a single
component, an intimate knowledge of the function of each part in a
module is not essential to the technician.
Complete schematic diagrams of the various circuits were used instead of
partial or simplified diagrams. This will allow the technician to identify
all components of a particular circuit without tracing the interconnecting
lines used in the complete instrument schematic which is bound in the
back of this manual. Whenever possible the location of components in the
diagrams located in the text is indicated; however, the complete
instrument schematic should be consulted to verify component locations
and intermodule connections.
Servicing information contained in this manual is divided into two chapters.
The first of these discusses techniques and procedures for rapid
servicing either in the home or the shop. The final chapter goes into greater
detail and considers those areas of servicing which require the
facilities and equipment normally found only in the service shop.
GENERAL
DESCRIPTION
The RCA CTC 49 chassis is a fourth- generation prises many of the basic circuit configurations of
solid-state color receiver, employing, for the first the CTC 40, upgraded in many respects, plus the
time, plug-in modules for most of the essential high-voltage quadrupler and motorless remote
functions. The CTC 40 chassis, introduced in 1968, control of volume, tint, and color, from the CTC 47.
is the first of the RCA solid-state color receivers;
The CTC 49 is a natural outgrowth of these prede-
however, a vacuum-tube high-voltage rectifier was
cessors; however a number of radical changes
used in that instrument. Next in order of introduc-
tion was the RCA CTC 47 chassis ( the G-2000), have been made. Two of these are perhaps equal-
which was released in 1969. This instrument re- ly significant. These are modular construction, and
tained most of the circuits used in the CTC 40, but the extensive use of integrated circuits. Other ad-
several significant changes were incorporated in vances include active side- pincushion correction,
its design. The electronically tuned VHF tuner and transformerless vertical output, matrixing of the
signal-seeking UHF tuner of the CTC 47 are im- color- difference and luminance signals before they
portant advances in the state of the electronic are fed to the kinescope, significant changes in the
art, and because of their spectacular perform- convergence circuits, and a 110 color kinescope.
ance they tend to overshadow two other important These will be described in this book, but before
advances. These are solid-state high-voltage rec- proceeding to circuit descriptions, an overall
tification, using a voltage quadrupler, and motor- examination of the chassis is in order.
less remote control, of volume, tint, and color.
Figure 1-1 is a block diagram of the RCA CTC 49
The RCA CTC 44 chassis represents the third gen- chassis. A total of eleven plug-in modules is
eration of solid-state color receivers and corn- used; a brief description of each module follows:
1
UHF
ANTENNA
UHF AUDIO DRIVER
MODULE PM 200
TUNER AUDIO 0 301
--11e. SOUND DETECTOR
SPEAKER
4.5- MHz AUDIO PREAMP AUDIO OUTPUT
VHF SOUND IF 0103
ANTENNA
AF T
CHROMA
MODULE MAK il CH MODULE MAC
VHF SIGNAL I PIX IF CHROMA ROMA BANDPASS
MODULE MAE
TUNER AGC REFERENCE OSC 3 58 REF ICHROMA DEMODS
AGC AFT
kT VIDEO PREAMP
ACC
AFPC
R- Y
BLACK AND WHITE BY
G Y
1
VIDEO
MODULE MAH MODULES MAD RED VIDEO
HORIZ AFC MODULE MAL B- W 3 ARE USED-- ONE
FIRST VIDEO AMP BLUE VIDEO KINESCOPE
HORIZ OSC SYNC SECOND VIDEO AMP FOR EACH COLOR
VIDEO GREEN VIDEO I CATHODES
SYNC SEPARATOR COLOR VIDEO OUTPUT
AMPLIFIERS
HORIZ MODULE MAG YOKE
CONVERGENCE CONVERGENCE
VERT SWITCH VERTICAL
TRIGGER VERTICAL OUTPUT CURRENT BOARD ASSEMBLY
fie
VERT PREDRIVER Q101-0102
YOKE CURRENT
VERT DRIVER PHUOLRSIEZ PW 800
· Ile. VERT YOKE
SIDE PIN CORRECTION
SWEEP AND H. V. HORIZ DEFLECTION
RETRACE H.V. QUADRUPLER SIDE
REGULATOR SCR 101- SCR 102
PINCUSHION
0401-T402 FLYBACK XFMR AMP
PULSE
KINE SCREEN SUPPLY FOCUS BLEEDER
CONVERGENCE
11*-1 220 ( VIDEO)
-
1
BOARD PW 800GATEAGC HIGH VOLTAGE
MODULE MAB +160 ( HORIZ) in. BURST GATE
FOCUS VOLTAGE
LOW- VOLTAGE +77 ( VERT) HORIZ AFC KINE SCOPE
RECTIFIERS m- + 30 ( AUDIO) SCREEN VOLTAGE
a.. + 30 ( DIST) YOKE CURRENT
HORIZ YOKE
Figure 1-1 Functional Diagram of the RCA CTC 49
Module MAK
The active devices in this module are two transis-
tors and two IC's. IC 1contains all the IF amplifiers
and the keyed- AGO circuit. IC 2 is used for AFT.
Q1 is the voltage regulator transistor for IC 1. 02
is the video preamplifier, an emitter follower which
couples the video detector and amplifier contained
in IC 1 to modules MAC and MAL.
Module MAC
The single active device in this module is IC 1,
which performs all the functions of the chroma-
bandpass amplifiers, color killer, ACC, AFPC, and
3.58- MHz reference oscillator found in earlier re-
ceivers. In addition, a DC reference voltage devel-
oped in this IC is used as control voltage for the
voltage regulator of Module MAE. In turn, regu-
lated voltage, --I11.2 volts, is supplied to this mod-
ule from Module MAE.
Module MAE
This module performs functions similar to the dis-
crete- component chroma demodulators and color-
difference amplifiers of the OTO 40 and OTO 47.
All this is performed in IC 1. The single transistor
in this module, 01, provides regulated 11.2 volts
for Modules MAC and MAE.
3
Module MAL
Two video amplifiers and the sync separator are lo-
cated in this module. The brightness limiter,
brightness control, peaking control, and contrast
control ( located on PW 300) are connected into
this module.
Module MAD
Three of these modules are used, one for each
color of video. Black- and- white video from MAL
is fed to all three of the MAD modules; the appro-
priate color- difference signal from MAE is applied
to each of them. The outputs of the three MAD
modules are fed to the cathodes of the kinescope.
Two transistors are used in each MAD module.
Module PM 200
The sound detector, which recovers audio from the
4.5- MHz sound signal, and the low-level audio
amplifier are combined in a single integrated cir-
cuit which is mounted with several passive com-
ponents in this plug-in module.
Module MAB
Six diodes, used as power- supply rectifiers, part
of the degaussing circuit and several minor com-
ponents are located on Module MAB. The power
transformer and filter capacitors are located on
the main chassis.
4
Module MAH
The circuit of Module MAH is similar to the hori- 9u608.50!
zontal AFC and oscillator circuit of the CTC 40 2741023-5
chassis. Q1 is the sync phase splitter and Q2 is
the blocking-oscillator transistor. One additional
active device, Q3, is used in the AFC system.
Module MAG
The vertical-deflection system uses the Miller cir-
cuit, familiar from its use in several earier solid-
state receivers. The switch, predriver, and driver
stages are in this module. The vertical-output
transistors are mounted on the main chassis.
Four major boards are used. PW
200 mounts various controls--
contrast, noise, the three screen
controls, kine bias, height, ver-
tical hold, and the three- position
service switch. PW 300 serves as
the parent board for all modules
except MAB, MAH, and MAG.
The audio-driver and brightness-
limiter transistors, Q301 and
Q302, the three kine drive con-
trols, plus various passive com-
ponents also are mounted on PW
300. Modules MAH and MAG are
mounted on PW 400, as are most
of the components of the hori-
zontal deflection and high volt-
age systems, the high-voltage
regulator, and the side- pincush-
ion amplifier and control poten-
tiometer.
5
The main chassis mounts the power transformer ings are deleted from this schematic) and S102
power-supply filters, the audio- output trans stor is the Normal/High line switch. At turn- on the re-
two vertical- output transistors, high - -
vol age quad- sistance of AT 1 is low and the degaussing current
rupler and focus bleede- and the SCR's and di- is high. As R 1 warms, its resistance increases
odes of the horizontal-deflection system. The until the degaussing current approaches zero.
power supply utilizes a transformer; however, one After warm-up the voltage drops across R4 and
side of the AC line is connected to the chassis. RI 1 are equal to the voltages across the upper
The DC outputs and their principal uses are as and lower transformer windings, respectively, mak-
follows: ing the voltage across the degaussing coil zero.
The current which still flows through R4 and RT 1
1. The 220-volt source powers the kine div-
keeps the latter warm, to maintain its high resist-
ers, Modules MAD A half-wave rectifier and
ance.
an RC pi filter is used.
2. Four diodes in a bridge configuration pro-
vide two outputs. One of these provides
about 77 volts to the vertical- output transis-
tors. Capacitive filtering is used. The sec-
ond output is divided into separate sup-
AC {
plies--one for the low - leve" transistors
throughout the instrument; the other for the
audio system. Both are nominally 30-volt POWEF
sources and both use RC pi ' ilters.
3. A half-wave rectlfier with an LC pi filter sup-
plies 160 volts to the horizontal deflection
system.
As illustrated in the schematic diagram, Figure 1-2,
the degaussing circuit is rather unusua . T101 is
the power transformer ( for simplicity several w.nd- Figure 7-2 Simplified Degaussing Circuit
6
RF and IF SYSTEM
Except for a minor change in the biasing of the The familiar " link circuit" which has been used
RF amplifier and revamping of the mixer output to with minor variations for several years has been
lower its impedance, the KRK 165 VHF tuner used replaced by a terminated coaxial line which inter-
in the CTC 49 is the same as the KRK 142 of the connects the tuner and the IF amplifier. This coup-
CTC 40 chassis. Both are four- tuned- circuit, wafer- ling method makes the tuning of the mixer and the
switch tuners using a MOSFET RF amplifier, a IF- amplifier input independent of each other; also,
cascode type mixer, and AFT controlled local os- the length of the interconnecting cable no longer
is critical.
cillator.
The mixer- output circuits of the KRK 142 and
In the KRK 165, AGC bias is applied to only one
KRK 165 are shown in Figure 2-2. Operation of
gate of the MOSFET, instead of both gates as in
the " Low C" output circuit of the KRK 142 was
the KRK 142. This circuit change is shown in Fig-
amply explained in SOLID STATE COLOR TELE-
ure 2-1. VISION, to which the reader may refer. In the
KRK 165, the 82-pF capacitor has been removed
and a 47- ohm resistor has been inserted in series
with the output.
As it will be explained later, the input impedance
DRAIN
AGC of the IF amplifier is nominally 50 ohms. Therefore,
INPUT
SOURCE it is desirable that the output impedance of the
mixer, as seen " looking back" from the IF ampli-
fier, also be nominally 50 ohms. As seen from the
NOT IN El+
KRK 165 output, the combination of L1 and C1 is a series
resonant circuit which has a very low impedance
RF INPUT
to ground, and this impedance is in series with the
47- ohm resistor. Thus the link cable itself, type
AG 58A/U, is terminated by its characteristic im-
Figure 2-1 Simplified RF Amplifier pedance, and its length is not critical.
7
+15 + 15
47
IF OUTPUT
IF OUTPUT
Li
Cl
12pF
BIAS
BIAS
1000pF
SIGNAL
INPUT SIGNAL
INPUT
A. KRK 142 B. KRK 165
Figure 2-2 Mixer Output Circuit of the KRK 142 and KRK 165 Tuners
IF INTEGRATED CIRCUril
As stated in Chapter 1, all IF amplification and the
is amplified and conducted from terminal 2 of the
generation of AGC voltage is accomplished in a IC to the sound module, PM 200.
single integrated circuit, IC 1, mounted in the IF
module, MAK 001A. While the actual circuitry of The second output from the interstage coupling
the IC may be of academic interest, a rigorous circuit reenters the IC at terminal 13 and drives an
emitter follower which has two outputs. One of
discussion is beyond the scope of this book. For
these outputs leaves the IC at terminal 14; the
the present purposes, an examination of the func-
other passes through the third IF amplifier to the
tional block diagram of the IC and an explanation
video detector. The video detector has three out-
of the surrounding discrete- component circuits
puts, one to the noise- immunity circuit, a second
will suffice.
to the AGC keyer, and a third to output terminal
Referring to Figure 2-3, the IF signal from the 19. At this point, the video white level is about + 7
volts and sync- tip level is about . 7 volt.
tuner ultimately is developed across L4 and in-
jected, along with AGC voltage, to input terminal The precise manner in which keyed AGC voltage
6 of the IC. The first IF amplifier actually consists is developed and made immune to sync- tip noise
of two emitter followers and a common- emitter am- spikes is rather unconventional; but since these
plifier. The second IF is essentially a common- functions take place entirely within the IC, they are
base circuit. As signal passes through these cir- of no particular interest from the standpoint of
cuits, the AGC voltage is stripped off, modified by servicing. The output of the AGC amplifier passes
the external noise control, and fed back to the from terminal 4, through a filter circuit, and then
signal shunt to control the gain. The output of the back into the IC at terminal 6, along with the IF
signal.
second IF stage appears at terminal 9 of the IC.
The block connected to terminal 18 is passive,
The interstage coupling circuit is a capacitively
containing the equivalent of two zeners and a
coupled, double tuned system, from which are de-
diode connected in series. A 12-volt drop is
rived two outputs. One of these is fed to terminal
provided for the base of the voltage regulator used
12, where it is amplified and detected. The 4.5-
to supply power to several devices in the inte-
MHz intercarrier signal generated in this detector grated circuit.
8
01 BASE
2
SOUND
IF AMP el 4.5-MHz AMP --0--e-
DST
14
AFT
gm-
INPUT
6 9 INTER STAGE 19 VIDEO
1ST & 2ND
IF INPUT BD - o COUPLING
IF AMPS OUTPUT
CIRCUIT 13
L4
s.
3
NOISE AGC KEYING
AGC AMP
IMMUNITY KEYER d PULSE
o 7
111
4
NOISE TUNER
CONTROL AGC
Figure 2-3 Functional Diagram of the IF/AGC Integrated Circuit
11111111 =J1IER-IF 'LINK CIRCUIT
Ti
39.75
C2 C3
5.1 I 5.6
FROM
TUNER
MAK 001A
Figure 2-4 Traps and IF Input Tuned Circuits
9
Signal from the mixer in the VHF tuner is con- and C6, and the series resonant circuit formed by
ducted through 50-ohm coaxial cable to PW 300, L3 with 010, C11, and 012. Therefore, the input
and thence to the MAK module. Passing through impedance seen at Cl is nominally 50 ohms,
Cl and R1 ( Figure 2-4), it next encounters the matching the impedance of the link cable.
parallel paths offered by C2 and C3, Li, C4 and
The coupling network consisting of L3, 010, and
05, and R2. Traps tuned to 39.75 MHz, adjacent-
C12 ( Figure 2-4), and L4 ( Figure 2-5) tunes the
channel video carrier, and 47.25 MHz, adjacent-
input of the first IF amplifier, located inside IC 1A.
channel sound carrier, are connected as shown.
The adjustment of these components is similar to
Li is a low-Q tuned circuit adjusted for best null-
the alignment of the link circuit of many earlier
ing of the 47.25- MHz trap. From the parallel paths receivers, L3 is tuned to the center frequency of
named above, paralleled paths to ground ( having
the IF passband ( about 44 MHz), L4 principally
an equivalent resistance of about 18 ohms) are controls the tilt of the response curve, and C12 es-
provided by R3, the parallel resonant circuit of L2 tablishes the bandwidth.
AGC AND NOISE CONTROL
NOISE
CONTROL
+15 -
41 +30
25KA irArl
14 R317
47
MAK 001A C13 R8
.01 18K
C20
1
R4
1.3
L4 10 TP 3
FROM
C12 4 · TO
L6
_L C19
10
+30V
C17 DIST
SERVICE C15 R6 =-"
SWITCH o s I 1 - .001
-1-
- 001
' 3.3K
-r R10 R11
oR
-
-=··7 100K 4.7K
I15 11
VV\.
, IVV\e- 111-11---/VV\i-·
R9 R12
56K T
- C16 __. C21
10K
± 10e
·
13
R303
R302 180K
470K TUNER
AGC
R305 CR 301 R304
27K 1.8M
NEGATIVE CR 302
HORIZ C301 R310
RETRACE .01 § 12K
R307
3.3K
+15-s
Figure 2-5 First and Second IF Amplifiers and AGC Circuits
10
R10 is the collector load resistor of the AGC- noise no longer is detrimental, and the gain of the
amplifier transistor located inside the IC and con- RF amplifier is reduced progressively by the AGC
as stronger signals are received. This is called
nected to terminal 4. Depending on the level of
AGC delay.
input signal to the receiver, the voltage at terminal
4 will vary slightly, above and below to about + 2.7
In the OTO 49 chassis, the AGC voltage from ter-
volts. As it becomes more positive. the IF gain is
minal 7 of IC 1 ( Figure 2-5) is more positive than
increased. This voltage is applied to the bottom of
+6.7 volts under no- signal conditions, but the
L4, and thence to terminal 6 of the IC along with
diode action of the zener, CR 302, clamps the
the IF signal.
amer AGC voltage to + 6.7 volts. As signal strength
is increased, the terminal- 7 output drops, and falls
Notice that when the service switch is in the nor- below 6.7 volts at about 1000 microvolts; however,
mal position one end of R9 is grounded. In either until this point is reached, the gain of the RF tuner
the raster or service position of the switch, the is maximum and receiver gain is controlled by
ground is removed and R9 is connected via R302 the IF AGC.
to the anode of CR 301, which has a potential of
about 100 volts. The portion of this voltage Further increasing the signal beyond 1000 micro-
which is applied to terminals 4 and 6 of the IC volts ( nominal) causes the tuner AGC voltage to
cuts off the IF amplifier for servicing. swing downwards from 6.7 volts toward a nega-
tive maximum. When it reaches - 5 volts, CR 302
conducts in the zener mode, preventing a further
Before discussing the operation of the noise con- negative swing. This is the minimum- gain operat-
trol and tuner AGC circuits of Figure 2-5, it is ap- ing point of the RF amplifier. Beyond the point
propriate to review the fundamentals of AGC where the tuner begins operating at minimum
operation. Since the output level from the video gain, the gain- controlled IF amplifier again con-
detector must be held constant, it is obvious that trols overall gain.
the receiver gain to this point must be made in-
versely proportional to the signal strength. This, To summarize AGC action, there are three distinct
of course, is the purpose of AGC. Since the range modes of operation, depending on signal strength:
of signal strengths which a receiver must process
may vary from perhaps 15 microvolts to 150 milli- 1. No signal to about 1000 microvolts-- RF
volts, the ratio of receiver gain from maximum to gain is maximum to provide best possible
minimum is in the order of 10,000:1. To design a signal-to-noise ratio of the receiver. IF AGC
single stage having this much dynamic range is maintains constant video output from the
difficult; but two amplifiers each having a dynamic detector.
range of 100:1 will fulfill the same requirement and
are more easily constructed. For this reason, the 2. About 1000 microvolts to perhaps 100 milli-
gains of both the tuner RF amplifier and the first volts-- RF gain is decreased by the AGC
IF amplifier ( and sometimes the second IF ampli- voltage to maintain constant output from
fier) are controlled. the video detector. IF gain is substantially
constant.
The ability of a receiver to produce a useful pic-
3. Above about 100 millivolts-- RF gain is held
ture from a very weak signal depends upon the
at minimum to prevent overload of the
amount of noise generated within the receiver it-
mixer, and IF gain is decreased by AGC
self. Since most of this harmful noise is generated
to maintain constant video- detector output.
in the tuner, it is desirable to amplify the signal
as much as possible in the RF amplifier, to main-
The function of the noise control is to allow the
tain the ratio of signal to noise as great as possi-
service technician to predetermine the amount of
ble. For this reason it appears that it always
signal strength at which AGC operation shifts
would be desirable to operate the RF amplifier
from the first to the second mode and, of course,
at maximum gain; however, this could cause from the second mode to the third. For example.
the mixer to overload and produce beats during in a suburban or rural area where all signals are
reception of strong signals. The solution to this relatively weak, the noise control may be set to
problem is to design the AGC system so that the allow maximum RF gain ( and minimum noise); in
RF amplifier operates at maximum gain on all a strong- signal area, the noise control may be set
signals weaker than some predetermined level, to minimize RF gain and the possibility of mixer
perhaps 1000 microvolts; above this level, tuner crosstalk.
11
IF, VIDEO PREAMP, AND AFT
The schematic diagram in Figure 2-6 shows the MHz intercarrier sound signal, and amplify it for
remaining section of IC 1and those external circuit injection into the sound module, PM200.
components which connect to it. Notice that L5,
C19, and C20 are shown on both Figures 2-5 and The IF signal fed into terminal 13 is amplified, de-
2-6. Signal from the second amplifier appears at tected, and amplified; the resulting video signal
terminal 9 of the IC and is coupled to the third IF appears at terminal 19. The video signal at this
amplifier input, terminal 13. point has a peak-to- peak amplitude of about 6.3
volts with negative-going sync; sync-tip level is
The collector of the second IF is tuned to about about + . 7 volt. Passing through the 4.5- MHz trap
the center of the IF passband ( 44 MHz) by L5 and and the preamplifier, Q2, the video is fed from the
019. Energy is coupled via C20 to L6, which is IF module to the video module, MAL. A second
tuned to remove tilt from the response curve. 41.25- output from the preamplifier is developed across
MHz sound- carrier energy is removed from the
the chroma peaking coil L7, and fed to the first
IF signal before it reenters the IC at terminal 13, chroma module, MAC.
but this energy still is present at the take-off point
to the IF amplifier whose input is at terminal 12. QI is a regulator transistor which supplies voltage
As stated earlier, the circuits in the IC between to a number of devices in the integrated circuit.
terminals 12 and 2amplify the IF, produce the 4.5- Base voltage for QI is established by a 12-volt
+30
MAC R324
2.2K
MAL
+30 C32 C31
TO AFT
R22
160 56
330
R11 6 C26
R15 R1
27K C21
8.2K 330 . 022
1000 1.8 C33 3
01 IF C27 L12 1- 160
C28
VOLTAGE
120
REGULATOR 680
C19
10
I
I R18 C29
02
330 180
VIDEO
C20
PREAMP
1.3
R19 R21
IC 1A
F- · 1K 1K
R13
L11
2.2K C25 --
12
L- - 11
4.5 MHz
C22 TRAP
3.6 T4 ( 41.25 _L C23
I
220
L10
I -
01 15 H
MAK 001A 10
19
R318 4.5 MHz
FLYBACK 10K
TO PM 200
PULSE /VV\i
Figure 2-6 IF Output and Video Preamplifier
12
R23
1200
± 30
C30 C36
T . 022 001 -
10
I
FROM IF 7
AMP
C35 L9
L8
82 - _LC34
62
T
R24 R25
C37
1K 1K
.001 T
4 MAK 001A
AFT
Figure 2-7 AFT Integrated Circuit and Discrete Components
zener regulator in the IC, making the regulated The AFT circuit, shown in Figure 2-7, is similar to
voltage at terminal 15 nearly 11.3 volts. In some the one used in the CTC 42 chassis. Only two ad-
modules, a diode may be found connected be- justments are necessary; L8 is adjusted for sym-
tween IC terminal 18 and the base of Q1. This metrical response around 45.75 MHz, and L9 sets
raises the base and emitter voltages of Q1 to 12.7 the crossover point to this precise frequency. The
and 12 volts, respectively. The increase in supply AFT output at terminals 1 and 4 " rides" on a DC
voltage is necessary for some IC's to provide suffi- level of about 6.7 volts.
cient video output.
13
THE VIDEO SYSTEM
In the past, the majority of texts describing color portant being the fact that both the chrominance
television receivers have treated the monochrome and luminance signals are processed in many of
video circuits separately from the chroma video the same circuits. Figure 3-1 shows the general
circuits. In this book, several reasons prompted configuration of the complete video- processing
the departure from this precedent; the most im- system.
POS. HORIZ RETRACE
·
VERTICAL RETRACE BRIGHTNESS
CONTROL 8,
CONTRAST CONT LIMITER
a.-
PEAKING CONT
IT1
- -
RED
FIRST SECOND
VIDEO VIDEO
OUTPUT BIAS
AMP AMP
AMP CLAMP
VIDEO
SYNC
PRE AMP
SEP
MAL MAD
NEG HORIZ RETRACE-- --
BLUE
AFPC
REF OSC
OUTPUT BIAS
CHROMA BANDPASS
AMP CLAMP KINE
COLOR CONTI BLANKING
CATHODES
ra, ACC
MAD
MAC I
REF
CHROMA
GREEN
VOLTAGE
REG
OUTPUT BIAS
DEMODULATORS
AMP CLAMP
DIFFERENCE AMP
TINT CONTI
to-
MAD
MAE
Figure 3-1 Functional Diagram of the Video System
15
From the video preamplifier situated in Module and reference oscillator. AFPC, ACC, color- level
MAK, video is fed to the video/sync module MAL, control, and burst blanking also are accomplished
which contains the first and second video ampli- in this module.
fiers as well as the sync separator. The positive
sync pulses from the sync separator have a peak The 3.58- MHz reference signal and the chroma
amplitude of 30 volts and are routed from the signal are conducted from MAC to the second
module without processing. chroma module, MAE, which is the chroma de-
modulator and color- difference- amplifier module.
The functions of luminance delay, vertical and The three color- difference signals, R- B- and
Y, Y,
horizontal retrace blanking, control of contrast, G- are conducted from MAE to the three kine
Y,
and control of video peaking are performed in the driver modules. An 11.2-volt regulator which pro-
first video amplifier. Depending on the setting of vides voltage for MAE and MAC is located in the
the contrast control, the stage gain varies from MAE module; as is the tint control input circuit.
about . 3 to unity or slightly more. Since the video
output is taken from the collector, video polarity While those portions of the video system discussed
is inverted in the stage and the output is positive- thus far bear at least a similarity to the ones found
going towards black level. A shunt filter between in many earlier chassis, the matrixing of luminance
the first and second video amplifiers attenuates and chrominance video outside the kinescope has
3.58- MHz video. not been done in an RCA color receiver since the
CTC 2 chassis was discontinued. Although several
The second video amplifier is an emitter- follower advantages are realized, the most significant is
stage which provides an impedance match be- that the load offered by the three kinescope cath-
tween the first video amplifier and the three paral- odes may be divided equally among three moder-
lel- driven kine-drive modules, MAD. Bias for the ately rated drivers instead of one relatively high-
base of the second video amplifier is controlled by power device, and, of course, the three kine-con-
the brightness control and the brightness limiter. trol-grid drivers are eliminated.
A negative- going horizontal- retrace pulse is fed
to the emitter to enhance operation in the vicinity Three identical modules, MAD, are used to drive
of black level. Since this is an emitter- follower the three kine cathodes. Insofar as the luminance
stage, the polarity of the output is the same as the signal is concerned, they are driven in parallel,
input. but each is driven by its respective color- difference
signal. Thus the outputs are true color-video
A peaking coil in the video preamplifier restricts signals, red, blue, and green. In addition to an
the bandpass of the signal fed to the first chroma output amplifier, each module contains a bias
module, MAC, to frequencies nominally between regulator stage which stabilizes the DC operating
3.08 Mz and 4.08 MHz. All active devices in this point of the output amplifier by returning the out-
module are contained in a single IC which serves put voltage to the same point during each horizon-
as a chroma-bandpass amplifier, burst amplifier, tal- blanking interval.
MODULE MAC
The functions of the integrated circuit, which con- burst amplitude ( which also affect oscillator drive)
tains all the active devices in MAC, is shown in cause the ACC system to control the gain of the
Figure 3-2. Notice the similarity of functions to first chroma-bandpass amplifier.
those in the CTC 38 chassis. Two stages of chro-
ma-bandpass amplification and an emitter fol- Figures 3-3 and 3-4 show the complete circuit of
lower make up the chroma amplifier. Gain of the Module MAC and also those components which
first amplifier is controlled by ACC and the color are not in the module, but directly connected to
control sets the gain of the second. Burst blanking it. The division of the circuitry between the two
and killer bias also are fed to the second bandpass figures is purely arbitrary; interconnections be-
amplifier. tween the circuits exist but they are within the IC
and do not appear in these schematics.
Burst is gated and amplified in the burst amplifier,
after which it is used to control the phase of the The chroma-bandpass signal from the video pre-
injection- locked reference oscillator. When burst amplifier is coupled through C10 ( Figure 3-3) to
is present, oscillator drive is increased and this terminal 1 of the IC and then to the base of the
operates the killer to turn on the second chro- input transistor of a cascode type amplifier. R8
ma-bandpass amplifier. Similarly, changes in and R10 fix the base bias of this device. The tank
16
15
COLOR
CONTROL
FIRST 0.1 SECOND EMITTER-I 14
1 CHROMA
CHROMA iBANDPAS
k _04 BANDPASS FOLLOWER OUTPUT
INPUT AMP
1. AMP,
KILLER 4
CONTROL-
12 - VOL11 6 TO VOLTAGE
KILLER -0---010"- REGULATOR
ZENER
MODULE MAE
10
HORIZ.
RETRACE °-
8 REF
-0-11e. OUTPUT
9
ACC CONTROL -0.-0--
(OSC STRENGTH)
Figure 3-2 Functional Diagram of First Chroma IC
circuit connected to terminal 16 tunes the output Burst blanking of the second chroma-bandpass
of this amplifier to about 4.0 MHz, near the upper amplifier is accomplished by the 30-volt positive
limit of the chroma passband. horizontal- retrace pulse which is divided and
timed by the network connected to the IC at term-
Inside the IC, signal is coupled from terminal 16 inal 10.
to the second chroma-bandpass amplifier, whose
output is tuned by the tank circuit connected to The tank circuit connected to terminal 13 may be
terminal 13. This tank is tuned near the lower limit excited by the leading and trailing edges of the
of the chroma passband, about 3.0 MHz. An emitter blanking pulse, producing a spurious ringing. For
follower in the IC couples the signal developed this reason, secondary blanking at the chroma out-
across this tank circuit to the chroma- output term- put has been incorporated in the design. The posi-
inal of the IC, terminal 14. R13 is the emitter load tive retrace pulse is coupled through R327 and
resistor for this emitter follower. Signal level at CR 305 to the emitter of the chroma- output NPN
terminal 14 can be as high as 1.5 volt at maximum transistor. This positive pulse cuts the transistor
chroma gain, and the DC level is about + 4.5 volts. off; betwen pulses, CR 305 isolates the retrace-
pulse input circuit from the chroma output circuit.
A voltage-operated gain control system is incorpo-
rated in the IC. The actual gain control voltage
The circuits having to do with reference-signal
appears at terminal 15, and is developed from two generation, ACC, and the color killer are shown in
sources. One of these is a voltage divider external Figure 3-4. The chroma signal from the first band-
to the chip, consisting of R9, R15, R4013, and the pass amplifier of the IC is conducted to a burst-
color control. Adjusting the control to increase the amplifier transistor which is gated on during hori-
positive voltage at terminal 15 increases the color zontal retrace time. In order to minimize variations
intensity, and the voltage at terminal 15 may be in the burst gating waveform which occur as the
varied from about 8.8 volts to approximately 9.4 kinescope beam current is changed, the positive
volts during color reception. 30-volt horizontal retrace pulse is clamped to
The second gain-controlling voltage at terminal +11.2 volts by CR 306 ( Figure 3-3). The resulting
15 is derived from the color killer, which is inside pulse is then integrated by R325 and C308 in
the IC. During monochrome reception or no-signal order to provide correct timing for burst gating.
conditions, the killer drives terminal 15 to a nom- The collector of the burst amplifier is connected to
inal + 4.5 volts, a level which cuts off the second the burst transformer at terminal 11. The reference
chroma-bandpass amplifier. oscillator is injection locked, similar to the system
17
-+- 11.2
COLOR
CONT.
7K
CHROMA