Text preview for : RCA Chassis 131,132.pdf part of RCA CTC 131, 132 RCA Chassis 131,132.pdf from EST 1984-10. Decription.
TV, service.
Back to : RCA Chassis 131,132.pdf | Home
A technical overview - Adapted from The RCA Com-
municator (an Electronics Tech-
nicians' Newsletter published
by RCA Consumer Electronics.)
T'he new RCA
The CTC 131 and CTC 132 color
chassis are the newest additions to
the RCA unitized chassis family.
The CTC 131 chassis is used in all
1985 (K -line) RCA ColorTrak 2000
CTC 131/132 25 -inch monitor -receivers. A varia-
tion of the CTC 131 chassis, the
CTC 132, is used in RCA's K -line
TV chassis
projection TV models.
The Color Trak 2000 monitor -
receivers give full spectrum audio/
video performance and have either
a 6- or 29-connection back patch
panel for direct hookup of stereo
and video devices. Also, all Color-
Trak 2000 monitor -receivers come
equipped for broadcast stereo and
with the Digital Command Center
infrared remote.
CTC 131/132 chassis have sever-
al new circuits. Among these are
ChromalLuminance Wide I Pro-
cessing, Automatic Kine Bias,
Broadcast Stereo Audio System
with Dynamic Noise Reduction
(DNR - trademark of National
Semiconductor), Chopper Power
Supply, Video Noise Reduction and
VideolAudio Switching Circuits.
Full resolution color
The unique characteristics of
human vision make certain colors
more perceptible at low light
levels. These colors center on
orange and cyan (blue-green). Less
perceptible colors are those
centering on magenta and yellow -
green. The NTSC color system ac-
commodates these characteristics
by transmitting the orange/cyan
(or I) spectrum with a higher
resolution than the magenta/yel-
low-green (or Q) colors. However,
the I signal, because of its wide
bandwidth, has the potential to
mix with luminance (detail) infor-
mation during processing. This
causes picture detail interference.
Figure 1. This 25 -inch console is one of 18 models in RCA's ColorTrak To avoid this, conventional color
2000 line that includes a built-in broadcast stereo sound system
capable of receiving BTSC stereo TV broadcasts (when availab e).
Editor's note: For the signal schematic for this
chassis, see the Profax schematic section in this
issue.
10 Electronic Servicing & Technology October 1984
www.americanradiohistory.com
televisions process only a fraction from each picture tube gun 60 Audio quality
of the available I color signal. times per second. This current is High -compliance speakers are
K -line ColorTrak 2000 monitor - compared to a stable reference, an integral part of the audio
receivers and projection televi- and when errors are detected, they system in all K -line ColorTrak
sions now include full resolution are instantly corrected. Warm-up 2000 models. These speakers pro-
color circuits that process 100 per- and aging drift are eliminated vide excellent reproduction and
cent of the NTSC broadcast signal. (along with the need for low -light high efficiency, even at higher-
These sets process the entire setup screen controls.). than -average volume levels. The
luminance bandwidth, for full speakers are driven by separate
detail performance; the entire Q Broadcast stereo audio system left and right amplifiers, for chan-
bandwidth, for more brilliant col- All CTC 131/132 chassis are nel separation during stereo pro-
ors; and the entire I bandwidth, for equipped for stereo TV broadcast gramming. Separate bass and tre-
reproduction of more subtle color reception. Each set provides full - ble controls permit TV audio to be
detail. RCA's charge coupled de- performance stereo sound from tailored to accommodate room
vice (CCD) comb filter (or detail stereo TV broadcasts without the acoustics. Also, when volume is
processor) virtually eliminates any need for set modifications or lowered, a built-in loudness con-
interference caused by luminance special equipment. A built-Li dbx tour circuit automatically boosts
and color mixing. And, the new decoding system reduces noise both bass and treble so that highs
chroma/luminance integrated cir- from specially encoded broadcasts. and lows are not lost as the sound
cuit performs the complex task of An LED indicator on the set lights level decreases.
converting the I and Q signals into during stereo programming, and a
the basic red, blue and green col- stereo/mono selector switch can be Monitor -receiver panel
ors that drive the picture tube. used to turn off the television's (Maxi monitor)
stereo processing circuitry in The 29-connection back panel
Video noise reduction fringe areas where the stereo permits direct hookup of up to
The new video noise reduction signal may not be strong enough three stereo video peripherals (in-
circuit minimizes snow and graini- for quality reception. cluding compatible digital R/G/B
ness in the dark picture areas, devices), plus numerous audio/
where these noise -related symp- Alternate audio channel video output applications. A 6 -con-
toms are most noticeable. It does reception nection back panel (not shown) is
this by automatically reducing the ColorTrak 2000 monitor -receiv- used on standard (or mini) Color-
degree of peaking (sharpness) in ers can also receive the alternate Trak 2000 monitor -receivers.
the darker picture areas. At the audio channel many TV stations
same time, sufficient peaking is may transmit for bilingual pro- TV broadcast stereo overview
maintained in brighter areas, gramming or other applications. A CTC 131/132 chassis incorporate
where detail is important but switch labeled Audio B can be set the new TV broadcast stereo/
where noise is not as apparent. for automatic selection of the al- Audio B multichannel receiver cir-
Also, because the video noise re- ternate audio channel when it is cuit. With this new stereo receiv-
duction sytem is dynamic, it transmitted. Separate LEDs sig- er, the TV viewer now can enjoy
senses and selectively adjusts the nal when Audio B programming is off-the -air stereo audio reception
peaking to match brightness. available and when the Audio B and select a transmitted secondary
switch is set for alternate channel audio channel (Audio B) containing
Automatic kine bias processing. The digital command bilingual information or back-
The emissions of the three guns center also includes an Audio A/B ground music to accompany the
in a picture tube must be optimally switch, allowing remote activation video portion of the program.
balanced to produce correct of the Audio B circuit. The TV broadcast stereo/Audio
whites. If picture tube setup is im- B audio transmission is comprised
proper, loss of color fidelity oc- Stereo from external component of a wideband composite audio
curs, and can cause an overall red, ColorTrak 2000 monitor -receiv- signal with several subcarriers.
green or blue tint in extreme ers (CTC 131/132 chassis) can pro- They are the conventional mono-
cases. With conventional color vide 2 -channel sound when a phonic L +R channel, the stereo
televisions, picture tube setup stereo VCR or other stereo audio difference information L -R (left
tends to drift during the time it source is connected to the monitor - minus right audio), and the Audio
takes the set to fully warm up receiver's audio input jacks. The B channel program. The stereo
(typically, about six minutes). Tube Dynamic Noise Reduction (DNR) subcarrier is twice the horizontal
setup also deteriorates as a televi- system automatically reduces scanning frequency, and is AM
sion ages. background noise and audio hiss modulated with suppressed car-
The new automatic kine bias (or on all program sources - off-air or rier. The Audio B program chan-
color balance) system dynamically VCR-without affecting the audio. nel is an FM signal centered at five
senses color imbalance during pic- The DNR system is activated by a times the horizontal frequency.
ture tube warm-up, and automatic- front panel control. An LED in- Both the stereo difference channel
ally maintains true color tracking. dicator lights when the DNR cir- (L - R) and the Audio B channel
A bias circuit samples the current cuit is active. signal are compressed at the trans -
12 Electronic Servicing & Technology October 1984
mitter in accordance with the dbx the RF signal that is transmitted IF stage generates a difference
TV noise reduction system. A pilot to the receiver. The receiver, in frequency between the pix and the
CW signal transmitted at the hori- turn, must tune the proper chan- sound carrier, developing a
zontal scanning frequency indi- nel, recover the RF signal, convert 4.5MHz sound IF signal.
cates the presence of stereophonic it back to baseband audio, in- The 4.5MHz sound signal is ap-
programming. dividually demodulate the various plied to the second sound IF
subcarriers and switch the ap- amplifier and demodulator circuit,
TV stereo broadcast audio propriate audio source to the audio which consists of a wideband
generation processing system in the receiver. 4.5MHz IF and demodulator. The
The simplified block diagram 4.5MHz signal is demodulated, and
shows how the broadcasting sta- TV stereo sound system the recovered baseband composite
tion generates the composite audio (Figure 1) audio contains the monophonic
signal. The left and right audio The complete sound system for audio. L -R stereo information,
signals are added together to form the CTC 131/132 chassis is con- and Audio B signals. The com-
the L + R (monophonic) signal. tained on one separate subas- posite audio is then routed to the
This signal is rolled off at 10kHz sembly. (The CTC 131/132 chas- Stereo/Audio B decoder circuit,
and passed to the input of the ad- sis contains no audio process- which recovers the L - R, the
der circuit along with a variety of ing circuits.) The audio processing Audio B and L + R information.
other signals required to develop assembly consists of three circuit The L -R and the Audio B infor-
the composite audio signal. To boards. These are the PWSB mation is applied to a switch cir-
generate the L -R audio channel, cuit that selects either the Audio B
the right channel signal is inverted signal source of the stereo broad-
and added to the noninverted left cast information.
channel. The L -R signal is pro- , Because the broadcast transmit-
cessed by a dbx compander circuit O 0 Ö<.,-0 ter performs only dbx companding
of the L -R and the Audio B
. a.
.,.,..o...,.
(encoder) to dynamically pre - O.Q, O 0 0 0 0 0
emphasize the signal characteris- signals, the receiver must expand
tics. This companded audio infor- OOÓ ._. only these two signals and not the
mation then is applied to an AM 0..00 Ö Ö characteristics of the L + R signal.
modulator with suppressed carrier o....a u..---me-fo Therefore, the L -R or Audio B
output. The carrier frequency for signal from the signal switch is ap-
this modulator is 31.468kHz (two plied to the input of the expander
times horizontal). The AM modu- circuit on the expander board. The
lated signal is applied along with Figure 2. Connection ColorTrak 2000 appropriate signal is then dbx ex-
the L + R signal to the output ad- maxi monitor rear patch panel. panded to its normal audio spec-
der circuit and combined with the trum characteristics. The L + R
15.734kHz pilot signal and the also is routed to the expander
Audio B information. (sound IF, demodulators and board and passed through an audio
The Audio B signal source is matrix), the PWEXP (dbx ex- delay circuit, to maintain the pro-
amplified and applied to the input pander), and the PWSS (audio per phase between it and the L -R
of an identical dbx compandor. volume/tone control, audio or Audio B signals. The delay must
The companded Audio B signal output). precisely match the expander
then is applied to the input of an Because of the wide baseband board circuit delay of the L -R or
FM modulator circuit, whose cen- audio, the sound IF signal cannot Audio B signals. This is necessary
ter frequency is 78.67kHz (five be processed by the pix IF circuit to optimize the channel separation
times horizontal). This FM modu- as it is in a conventional TV in the stereo mode. The L + R and
receiver. Instead, the IF signal
lated signal source is applied to the L - R/Audio B signals are routed
output adder circuit and combined output from the tuner assembly is back to the matrix amplifier on the
with the previously developed routed to two separate circuits: PWSB board. The matrixed out-
signals, forming the composite the pix IF circuit, and the new put signals then are passed to the
audio signal. The bandwidth of the sound IF system. PWSS board assembly. The signal
composite audio signal extends The pix IF output from the tuner is applied to a dynamic noise
from 50HZ to 94.404kHz. is routed through the IF link cable reduction (DNR) amplifier, which
The various carrier frequencies to the CTC 131 chassis board. reduces background noise in the
and the pilot signal in the com- Next to the IF jack on the chassis audio during low -amplitude, high -
posite audio signal are derived board is an additional IF jack frequency conditions. The output
from a reference system that is through which the IF signal is of the dynamic noise reduction
phase locked to the video horizon- routed to the receiver audio amplifier then is passed to the
tal sync. This minimizes problems subassembly. The 45MHz IF signal volume/bass/treble control circuit.
that might cause spurious radia- is applied to the first IF amplifier The audio then is sent to the audio
tion and beats. and detector network, which output circuit on the PWSS board,
The composite audio signal then operates at the same frqeuency as to drive the internal speakers in
is passed to a conventional video/ the pix IF system (45MHz). The the TV receiver of external
audio modulator, which generates detector circuit in the first sound speakers.
14 Electronic Servicing & Technology October 1984
On/off control operation logic Lo. The chopper regulator deflection system, the + 30V from
(Figure 2) then produces a variety of B + the output of the IHVT will not be
The CTC 131/132 TV chassis power sources, two of which power present, and the latch system
uses an electronic latching-type of the horizontal deflection system. within the tuner control module
power on/off control system. The The deflection system develops a will not keep the control line at a
tuner control module (MSC) con- variety of scan -derived B + 's, one logic Lo. As a result, the control
trols the on/off condition of the of which, the + 30V, is routed back line will immediately go logic Hi,
chopper regulator power supply. to a sensing circuit in the MSC turning off the power supply. This
An on/off instruction from either module. This causes the MSC operation takes only a few hun-
the IR hand unit or the manual module to latch the control line in dred milliseconds.
on/off switch activates a latch the logic Lo state, keeping the Also notice in the block diagram
within the tuner control module power supply turned on. that the horizontal deflection
microcomputer, pulling the control If a problem exists in the chop- system produces a shutdown
line to the chopper regulator to per regulator supply or in the signal that is applied to the chop-
per regulator circuit. If excessive
high voltage exists, the shutdown
command is applied back to the
Le11
LR chopper regulator circuit, turning
Stereo
Pilot off the output of the regulator.
15.734 kHz
31.488 kHz When the output of the regulator
12141
Compos Ir is turned off, the B + to the deflec-
Rgt o ENCODER I ----I
AM MOD
SUPPRESSED
O
Auem
tion system drops to zero, turning
CARRIER
i l 4--11
off the deflection system. At this
time, the power supply again turns
I I
AMI
on, applying power to the chassis.
At,O o 8
Awl w B
ENCODER
FM
MOD If excessive high voltage continues
7667 Hz 2
/
(FM.
:
to exist, the chopper power supply
will be toggled off and on until the
H
Ir
15111
Horiz
Sync
PLL
E78.67 kHz
31.468 kHz
problem is resolved.
REF 15.734 kHz
The chopper regulator should
never be forced into an on state by
defeating the protective feedback
Figure 3. TV stereo broadcast composite-audio generation. loop between the IHVT, MSC and
chopper power supply.
MONOPHONIC AM MODULATED - FM
AUDIO SUPPRESSED CARRIER MODULATED Automatic kine bias (AKB)
The CTC 131/132 automatic kine
bias (AKB) system (Figure 3)
%
R
,__,,_...,s
Stereo
Pilot
R Audio B
eliminates color temperature drift
problems that occur in conven-
tional receivers as a result of pic-
ture tube warmup and aging. A
AMPL dynamic circuit in the CTC
I J l
131/132 monitors the emission of
Freq - (X Horiz)
3 4 5 6
the three guns in the picture tube
and corrects the do bias of the
video driver stage to maintain pro-
Figure 4. TV broadcast stereo-composite audio. per gray scale (color balance). See
the simplified block diagram.
MST
TUNER
AOC
PI%
F/DET
r
I
-
ku 1 l
RWSB
The AKB circuit monitors
various gating signals within the
video driver circuit during a test
period called the AKB process
LR period. This period occurs during
P10.045.75 MHz
et SOUND
IF/DET
4.5 MHz
2no SOUND
iF/OET
STEREO/
AUDIO B
DECODERS
Audio B SW' the seven horizontal scan lines just
-41.25
SOUND MHz
after vertical blanking. (By reduc-
r r
I LR
-
AuiD
Ro
e
ing the vertical height of the
VOLUME/ DYNAMIC
R I receiver, the AKB period can easi-
To MATRIX
ly be seen at the top of the screen.)
I
BASS/ NOISE DELAY
Sokrs TREBLE AMP
REDUCI
CONTROL
The AKB process circuit requires
-J
T
vertical and horizontal pulses from
I
I I I
LPWSS L
the countdown integrated circuit
to properly time its operations.
Figure 5. Stereo sound system block diagram. During the AKB process period,
16 Electronic Servicing & Technology October 1984
the automatic kine bias circuit cess period, thereby controlling AKB setup
generates a variety of control the emission of the picture tube To properly set up the receiver
pulses to set the video output stage guns. Again, this AKB period oc- gray scale, place the setup switch
to a known state. A grid setup curs only during seven horizontal (on the kine drive board) in the
pulse is applied to the picture tube lines at the beginning of vertical setup position and adjust the AKB
grid from transistor Q5007. At the scan. Otherwise, the luma/chroma control (on the rear of the IHVT
same time, the AKB pulse and process, luma/chroma interface transformer) until one color just
AKB gate are applied to the (PWLCI circuit board) and video barely becomes visible on the
a
luminance/chrominance process drivers operate normally. The screen. Then, place the setup
circuit and to the luminance/ - AKB circuit eliminates the need switch in the normal position. The
chrominance interface board for three separate screen controls. AKB circuit now takes over and
(PWLCI), respectively. These In the CTC 131, one screen control continuously adjusts the drive bias
pulses from the AKB process cir- (AKB) is used to simultaneously to the video driver stages so that
cuit set up the inputs of the video adjust the screen potential to all the relative conduction of the pic-
driver stage during the AKB pro- three guns. ture tube guns maintain proper
gray scale. This correction is up-
dated 60 times a second (or every
vertical field).
Tuner Control
-
Module
"LO" TURNS ON
AKB timing (Figure 4)
PRE AMP
POWER SUPPLY
As stated previously, the AKB
processing period is the seven
On OH
R Ilpn LATCH
CHOPPER
REG
POWER
SUPPLY
129V
5v
Shutdown
MORII
DEFLECTION
-- Hv
23-
30.
horizontal lines at the beginning of
vertical scan. The vertical and
horizontal pulses from the deflec-
VOLTAGE
SENSE
tion countdown IC are used to
PRESENCE OF
.30 VOLTS LATCHES
time the operation of the AKB pro-
.3,
OUTPUT
cess system. As shown in the tim-
ing chart, at the end of vertical
Figure 6. CTC 131 PWM chopper power supply on/off control operation.
blanking, pin 13 of the AKB IC
develops a positive pulse that lasts
throughout the complete AKB
period. This output pulse is passed
VIDEO
DRIVER
to the chromalluma IC, instructing
the IC to fix the RIG/B outputs at a
38Vdc level during the AKB
PWLCI
LUMA/CHROMA BOARD VIDEO J I I
PROCESS DRIVER
-.-. ISWITCHABLE -3
-12 period. By using an oscilloscope
1 1
Chroma AC OROUNDI
VIDEO
DRIVER
AKB
synchronzied at the vertical rate, a
InputSandc VEB
AKB
Gate
a^gd
ZrBlaa
I Screen
Voltage technician can observe this AKB
Sense
Input
pulse and its effect on the R/G/Bt
AKB
Pulse
AUTO EINE BIAS
PROCESS
Setup
Pulse
outputs of the chroma/luma IC.
The setup pulse from pin 11 of
05007 the AKB IC occurs one horizontal
line after the start of the AKB
Vert
period. The setup pulse is passed
to transistor Q5007, is inverted,
Figure 7. Automatic kine bias (AKB) simplified block diagram. and then is applied to the grid of
the kine gun. This pulse sets the
reference point used during the
81
141ein AKB period to make the proper
measurement. The program pulse
Herz
Fiona
-ss- Tlmmg
from pin 12 of the AKB circuit is
,Pie 161
developed approximately four
horizontal lines after the start of
I
AKB
PIn 131
Sels Lume/Chrome
Outputs to 3 B VDC
IC
the AKB period, or at the end of
the setup period. The program
Setup
PIn III
Inverted By 05007
to Grld of Klne
pulse, referred to as the sense
period, has a duration of three
I
(Sets Measurement Ref,
Program Sent to KIne DrIve CE`
FOf Sense Measurement