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ELECTRONIC TECHNICIAN/DEALER JANUARY 1971
TEKLAB REPORT
The familiar "link circuit" has now been replaced
and the color -difference and luminance signals are
matrixed before they are fed to the CRT
Introducing RCA's Argosy
Portable Color -TV Set
by Joseph Zauhar
The Argosy portable color -TV include active side -pincushion cor-
set, with its CTC49 chassis, takes a rection, transformerless vertical out-
large step into the future with a num- put, matrixing of the color -difference
ber of radical changes. Two of these and luminance signals before they
important changes include modular are fed to the kinescope and changes
construction and extensive use of in- in the convergence circuits.
tegrated circuits. The television re- Specifications indicate that the
ceiver reportedly employs the first tuner may be exchanged without the
domestic use of the new, slimmer need for realignment of the coupling
110° CRT and has 11 separate circuit to the IF amplifier, while a
Accu Circuit modules, including 5 solid-state high -voltage quadrupler,
integrated circuits. Other advances which essentially is another module,
and the use of plug-in transistors
RCA Corp.'s Argosy Portable Model EP506W makes it possible to correct most
employing the CTC49XA chassis. failures with very little servicing ef-
the compact receiver is 4 in. slimmer than fort.
previous 18 -in. models. After the back cover is removed
the complete chassis is exposed for
servicing, the modules can be re-
moved from their edge contacts by
lifting two retaining clips. The main
chassis mounts the power transform-
er, power -supply filters, audio -out-
put transistor, two vertical -output
transistors, high -voltage quadrupler,
focus bleeder, and the SCR's and di-
odes of the horizontal -deflection sys-
tem.
Some of the circuitry has a close
resemblance to earlier RCA chassis
-such as the tuner, AFT and hori-
zontal deflection system, which are
similar to their counterparts in either
the CTC40 or CTC47 chassis; and
the sound moo, le which is almost
identical to the one used in the
CTC41, CTC42 and CTC43 chas-
sis. The integrated circuits used in
JANUARY 1971, ELECTRONIC TECHNICIAN/DEALER 33
the IF and chroma circuits are
packaged in a single unit and a
_
NOISE
_
CONTROL
+30
stage -by -stage review would have +15 -I,
2514V1
very little value to the technician. 14 R317
Because of space limitations this MAK 001A T
ci3
47
article reviews only some of the new K
circuits that should be understood if FROM
R4
10 TP 3
C20
1.3
L4
circuit troubleshooting is required. C12
C14 j_ Ta
W17 L5 C19
RF and IF System f T +30V
SERVICE 10 DIST
,,,. R6
The KRK165VHF tuner used in SWITCH d S
R
.vv. 93K 00, R11
the CTC49 chassis is the same as 15 4.7K
I
the KRK142 tuner of the CTC40 I I
R9
56K -1- C16 C21
,001
R12
10K
10,,F
chassis except for a minor change in 13
the biasing of the RF amplifier and R302
R303
revamping of the mixer output to R305
470K
180K
TUNERi4t
CR 301 R304
lower its impedance. Both tuners 27K
API
1.8M
R306
1000
are four -tuned -circuit, wafer -switch
tuners using a MOSFET RF ampli-
fier, a cascode-type mixer and an
NEGATIVE
HORIZ
RETRACE
C301
.01 0 CR 302
R310
12K
R307
AFT controlled local oscillator. +15
3.3K
The familiar "link circuit," which
has been used with minor modifica- Fig. 1-The First and Second IF Amplifiers and AGC Circuits.
tions for several years, has been re-
placed by a terminated coaxial line,
which interconnects the tuner and POS. HORIZ RETRACE
IF amplifier. This coupling method VERTICAL RE I RACE BRIGHTNESS
CONT ROLE
makes the tuning of the mixer and CONTRAST CONT LIMITER
the IF -amplifier input independent PEAKING COST FIRST SECOND RED
of each other; also, the length of the VIDEO
AMP
VIDEO
AMP OUTPUT BIAS
AMP CLAMP
interconnecting cable is no longer VIDEO
PRE AMP SYNC
critical. SEP
MAL IMAD
NEC HORIZ RETRACE- - -
AGC and Noise Control BLUE
The AGC and noise control cir- :nsc
CHROMA BANDPASS OUTPUT BIAS
AMP CLAMP KIWI
cuit is shown in Fig. 1. There resis- COLOR CONTI BLANKING
ACC CATHODES
tor R10 is the collector load resistor MAC I
of the AGC-amplifier transistor, lo- REF
cated inside the IC and connected at CHROMA-s-
terminal four. Depending on the lev- VOLTAGE
REG
GREEN
el of the receiver input signal, the DEMODULATORS
OUTPUT H BIAS
AMP
voltage at terminal four will vary TINT CONTI
41. -
DIFFERENCE AMP CLAMP
slightly, above and below +2.7v.
MAE
As it becomes more positive, the IF I
gain is increased. This voltage is also
Fig. 2-Functional block diagram of the video system used in the RCA CTC49 color chassis.
applied to the bottom of coil L4,
and then to terminal six of the IC no -signal conditions, but the diode -5v, zener diode CR302 conducts
along with the IF signal. action of the zener diode, CR302, in the zener mode, preventing a fur-
When the service switch is in the clamps the tuner AGC voltage to ther negative swing. This is the mini-
Normal position, one end of resistor +6.7v. As signal strength is in- mum -gain operating point of the RF
R9 is grounded. In either the Raster creased to 1000,u,v, the terminal amplifier. Beyond the point where
or Service position the ground is re- seven output voltage drops, falling the tuner begins operating at mini-
moved and resistor R9 is connected below 6.7v. However, until this mum gain, the gain -controlled IF
through resistor R302 to the anode point is reached, the RF tuner is op- amplifier controls overall gain.
of diode CR301, which has a poten- erating at maximum gain and re- The AGC action has three dis-
tial of about -100v. The portion of ceiver gain is controlled by the IF tinct modes of operation, depending
this voltage that is applied to ter- AGC. on signal strength:
minals four and six of the IC cuts Further increasing the signal be- No signal to about 1000µv-
OFF the IF amplifier for servicing. yond 1000µ,v (nominal) causes the RF gain is maximum to provide the
In the CTC49 chassis, the AGC tuner AGC voltage to swing down- best possible signal-to-noise ratio of
voltage from terminal seven to IC1 wards from +6.7v toward a nega- the receiver. IF AGC maintains con-
is more positive than +6.7v under tive maximum. When it reaches stant video output from the detector.
34 I ELECTRONIC TECHNICIAN/DEALER, JANUARY 1971
Pix IF
About 1000euv to perhaps 100 AFT
MAK Module
mv-RF gain is decreased by the Chrome I
AGC voltage to maintain a constant MAC Module
Sound
Vert
output from the video detector. IF PM 20C Module
MAG Module
gain is substantially constant.
Above about 100mv-RF gain
is held at a minimum to prevent
mixer overload, and IF gain is de-
creased by the AGC to maintain a
constant video -detector output.
The function of the noise control Power
is to allow the service technician to Supply
MAB Module
predetermine the amount of signal
strength at which the AGC opera-
tion shifts from the first to the sec-
ond mode and from the second
mode to the third.
The Video System
From the video preamplifier situ-
ated in Module MAK, video is fed
to the video/sync module MAL, as
shown in the functional diagram in
Fig. 2. This diagram shows the first
and second video amplifiers as well
Video Sync Horiz
as the sync separator. The positive MAL Module MAH Module
sync pulses from the sync separator Master
Off
have a peak amplitude of 30v and
are routed from the module without Red Grn Blu
processing. Chroma II Kine Drive
MAE Module MAD Modules
The functions of luminance de- Hi -line
lay, vertical and horizontal retrace Rear view of the CTC43 chassis exposing the 11 AccuCircuit modules. With
extensive use of modules, the chassis is compact and yet easy to service.
blanking, control of contrast, and
control of video peaking are per-
formed in the first video amplifier.
Depending on the setting of the con-
trast control, the stage gain varies
from about 0.3 to unity or slightly
more. Since the video output is tak-
en from the collector, video polarity
is inverted in the stage and the out-
put is positive -going toward the
black level. A shunt filter between
the first and second video amplifiers
attenuates the 3.58MHz video signal.
The second video amplifier is an
emitter -follower stage which pro-
vides an impedance match between
the first video amplifier and the Transistor
three parallel -driven kine-drive mod- QI
ules, MAD. Bias for the base of the All of the IF amplification and the generation of AGC voltage is accomplished in a single
integrated circuit IC1 mounted in the IF Module, MAK.
second video amplifier is controlled
by the brightness control and the the signal fed to the first chroma The 3.58MHz reference signal
brightness limiter. A negative -going module, MAC, to frequencies nom- and the chroma signal are conducted
horizontal retrace pulse is fed to the inally between 3.08MHz and 4.08 from the first chroma module to the
emitter to enhance operation in the MHz. All active devices in this mod- second chroma module, MAE.
vicinity of the black level. Since this ule are contained in a single IC, From there the chroma demodulator
is an emitter -follower stage, the po- which serves as a chroma-bandpass and color -difference signals, R -Y,
larity of the output is the same as amplifier, burst amplifier and refer- B -Y and G -Y, are conducted to the
that of the input. ence oscillator. AFPC, ACC, color - three kine-driver modules. An 11.2v
A peaking coil in the video pre- level control and burst blanking are regulator, which provides voltage
amplifier restricts the bandpass of also accomplished in this module. for modules MAE and MAC, is lo -
JANUARY 1971, ELECTRONIC TECHNICIAN/DEALER 35
cated in the MAE mod' is the
tint -control input circuit
The video system de , is
similar to the ones found iany .
earlier chassis-the matrixing f lu-
minance and chrominance video out-
side the kinescope having not been
done in an RCA color receiver since
the CTC 2 chassis was dicontinued.
Although several advantag,-, are re-
alized, the most significant is that
the load offered by the three kine-
scope cathodes may be uivided
equally among three moderately
rated drivers instead of one relative-
ly high -power device, and, of
course, the three kine-control-grid
drivers are eliminated.
Kine Driver Module, Mad
Three identical kine-drive mod-
ules, MAD, are used-one for each
color of video. In each module the
luminance video is combined with
one color of the chrominance video
(color Difference signal); the two
bits of information are then ampli-
fied and finally fed to the appropri-
ate kine cathode as shown in Fig. 3. By lifting two spring locks the modules can be easily removed from their edge connectors.
We will first consider the signal
paths: Luminance video passes from
the service switch to the emitter of
transistor Q1 through three parallel
paths. These are n sistor R7, called
the primary path of convenience; re-
sistor R6 and capacitor C2, which
provide high -end video peaking; and
resistors R335 and R336, which al-
low control of amplifier gain for
gray -scale setup. The color- 'Ter-
ence video, R -Y for example, ives
the base of transistor Q1, ana then
R -Y is added to Y to produce R, or
red. The color -video output is con-
ducted directly from the module to
the kine socket without passing
through the edge connector; the
spark gap and the 3.3K resistor are
in the kine socket.
The dc stability of the kine cath-
odes is provided by the positive hor-
izontal retrace pulse injected at ca-
pacitor C309 and conducted to the
bias transistor, 02. Considering
only the circuitry within the module,
observe that a feedback ..-;)n exists
from the collector of tr;, , .;s Jr 01,
through resistor R2, die .t. t :1, re-
sistor R9, transistor Q2. r ;sistor
R5 back to the emitter ';sistor
01. Assuming that then .1put The zorvergence board is placed around the neck of the CRT with spark gaps and resistors placed
signals, it functions as fo, rise in the :RT socket.
36 ELECTRONIC TECHNICIAN/DL A: tNUARY 1971
in the ,- ,e at the collector of
transistor 1., increases the emitter -
to -base c nt in transistor Q2; this
increases t le collector current of
transistor 02, which passes through
transistor Q 1. The increase in tran-
sistor Q1 collector current increases
the voltage drop across resistor R3
and drives the collector voltage of
transistor 01 back to its former
value. Conversely, a drop in collec-
tor voltage at transistor 01 decreas-
es the base forward bias of transistor
02, reducing the drop across resis-
tor R3 and returning the collector of
transistor 01 to its former potential.
Since the loop gain is fairly high
(greater than 20) the collector volt-
age of transistor 01 is held within
very close limits.
This explanation is oversimplified,
because it ignores two important
facts: Signals are present, so the col-
lector voltage of transistor Q1 must
vary; and no reference voltage has
been provided to c stablish the voltage
Fig. 3-Schemat c of a Module MAD Nine driver. The load from the three CRT cathodes is divided at which the collector of transistor
equally among three moderately rated drivers instead of one high power device.
01 is stabilized. There is, however, a
period when no signals are present
-the horizontal -retrace blanking
period. If the bias current through
transistor Q1 is set to produce kine
cutoff during blanking time and suf-
ficient integration is provided, this
amount of bias can be maintained
until the next blanking interval. This
integration is provided by capacitor
C1 .
The characteristics of the CRT
dictate that its cathodes, and the col-
lector of all transistor QI's, be driv-
en to +160v for blanking. A refer-
ence voltage, keyed ON only during
blanking, is conveniently derived
from the horizontal retrace pulse.
This pulse enters the circuit through
capacitor C309 and is limited to a
peak value of 220v by diode
CR307. This limited pulse is fed
through capacitor C3 to the stabiliz-
ing loop. In any pulse circuit the dc
level is equal to the pulse voltage
times the duty cycle. (Duty cycle is
definL d as the product of the pulse
widtt 'n seconds and the number of
pulse, - second; e.g., a horizontal -
retrace se having a width of Sps
has a cycle of 0.0787.) The
circuit ' ants in these modules
were select so that the average dc
Approximately 75 percent of the Argosy's circuitry is contained in these 11 plug-in modules. voltare a me junction of diode
continued on page 49
JANUARY 1971, 'JIC TECHNICIAN/DEALER 137
.1 I
being served by organized CB cover more than 50 percent of
groups. For example, REACT alone Ohio's land area and 75 percent of
has over 40,000 members monitor- its primary roads. As in the Detroit
ing CB Channel 9 24 hours a day. test, all emergency communications
An estimated 1000 independent are logged on IBM cards and tabu- TEKLAB
groups and many more thousands lated by computer for future study continued from page 37
of individual CB operators also offer and publication.
motorist assistance. And over 500 All of these factors . . . the very CR1, resistor R8 and capacitor
police and fire departments are healthy growth of CB radio in the C3 is 160v less positive than
known to be now monitoring 60's . the widespread and growing
. . the peak voltage at that point.
27MHz for emergencies. interest by responsible authorities Under ideal conditions, the
One project that has received na- in CB for emergencies . . the in-. voltage at the collector of tran-
tional attention is the Detroit, Mich. creasing interest of major retailers sistor Q1 would always return
CB Driver Aid Network, originally with the tremendous merchandising to +160v during retrace blank-
sponsored by General Motors Re- power available to them . . all are . ing. The 220v retrace pulse at
search Laboratories and now an on- indicators to me that we truly are on the anode of diode CR307,
going regular program administered the threshold of an explosion. To coupled through capacitor C3,
by the Bureau of Roads and Streets. bring into focus the character of this would be clamped at the tran-
In this system a central monitor, explosion . . . the what it is and why sistor Q1 collector voltage by
linked to strategically placed trans- it is going to occur . . . let me ex- diode CR1, and a constant dc
ceivers by land -line, receives calls on plore some of the basic marketing bias voltage at the base of tran-
CB Channel 9 and responds with the factors involved. sistor Q2 would be developed.
appropriate service required. We know that at present, despite In practice the blanking -lev-
Incoming calls are automatically a lot of emphasis on the business el voltage at the collector of
displayed on an illuminated map and professional applications for transistor Q1 may tend either
above the console, and the location CB, the fact remains that nearly 73 to increase or decrease. If it
is automatically pinpointed. Reports percent of all licensees are using should tend to increase, the re-
are tabulated and computerized. their equipment primarily for per- trace pulse is clamped to a
Since January 1969, over 1200 sonal and safety applications. higher potential, the bias at the
emergency calls per month have Looking at this segment of the base of transistor Q2 increases
been logged, 74 percent of which in- market today, it is obvious-to any- conduction of this semiconduc-
volved either accidents, stalled ve- one with ears-that a fair percent- tor and the collector voltage of
hicles, road construction or faulty age of these personal users are con- transistor Q1 is driven back to
traffic devices. cerned with hobby applications. I 160v. Conversely, a tendency
In March 1969, General Motors am convinced-and this is a view toward a drop in transistor Q1
Research Laboratories turned the shared by many responsible people collector voltage decreases the
Detroit program over to the city and -that the adverse impact of hobby bias current of transistor Q2,
undertook an even more significant activity will rapidly decline in the boosting the transistor Q1 col-
continuing research program when it 70's, through increased monitoring, lector voltage back to 160v.
assumed national sponsorship of the through the sheer weight of growth The process just described
REACT organization. In addition to by other types of users and through fulfillsthe requirements for
supporting and strengthening this the rapid decline of sunspot activity voltage stabilization. Sampling
national program, it authorized a anticipated from mid -1971 through of kine cathode voltage occurs
massive research program in the the 70's. during blanking time when no
state of Ohio. There will be a substantial in- signal voltage is present, and
Among other reasons, Ohio was crease in the importance and effec- the bias current established is
selected since 23 of the state's 57 tiveness of organized citizens radio maintained constant through-
highway patrol posts were already groups such as REACT monitors, out the scanning interval by
monitoring CB Channel 9 in coop- due to much greater participation by virtue of the integration in the
eration with REACT teams. public agencies (as in Ohio) and base -collector circuit of tran-
In the Ohio Test, a State Director the designation of Channel 9 strictly sistor Q2.
was appointed to work directly with for emergencies. Next month we will cover
state agencies, including the High- But the real market-marginal to- other important circuits of this
way Patrol which is officially spon- day, but the name of the game in the TV set, including the low volt-
soring and participating in the two- future-is the American public, us- age power supply, the active
year test program. Under the joint ing CB radio the way it was intend- side -pincushion correction cir-
control of the state agencies and ed by the FCC-for necessary per- cuit and the transformerless
state REACT director, REACT sonal communication. It is this mar- vertical output circuit.
teams function within rigid guide- ket that we are counting upon for Some of the information
lines on monitoring and communica- numbers like 64 million auto instal- used is based on the material
tion for emergencies. The REACT lations . . . and 7 million home in- supplied through the courtesy
emergency system is designed to stallations. of RCA Sales Corp.
ELECTRONIC TECHNICIAN/DEALER 49
ELECTRONIC TECHNICIAN DEALER FEBRUARY 1971
TEKLAB REPORT
The receiver's vertical feedback circuit,
known as a Miller run-down circuit, was seldom
employed before the advent of transistors,
due to its high gain requirements
Introducing RCA's Argosy
Portable Color -TV Set -Part II
Most of the repairs that might ing capacitive filtering, supplies ance increases until the degaussing
eventually be required for this chas- about 77v to the vertical -output current approaches zero. After
sis can be accomplished by module transistors. The second is divided warm-up, the voltage drops across
replacement rather than by replacing into separate supplies-one for resistor R4 and thermistor RT I are
single defective components. How- the low-level transistors used equal to the voltage drops across the
ever, it is still important to know throughout the receiver, the other upper and lower transformer wind-
how each circuit functions for more for the audio system. Both are ings, respectively; making the volt-
effective servicing or possible mod- nominally 30v sources and both age across the degaussing coil equal
ule repair. use RC -pi filters. Ov. The current, which still flows
Last month's Teklab Report re- A half -wave rectifier, with an through resistor R4 and thermistor
viewed the RF, IF, AGC, Noise LC -pi filter, is used to supply RT1, keeps the latter warm to main-
Control, Video and Kine Driver cir- 160v to the horizontal deflection tain its high resistance.
cuits, while this month we cover the system. Horizontal Deflection Circuits
power supply, and horizontal and As illustrated in the schematic di-
vertical deflection circuits, which in agram, Fig. 1, the receiver contains The CTC49 chassis employs a
many ways are different from com- a rather unusual degaussing circuit. horizontal deflection and high volt-
parable circuits in earlier RCA re- In this schematic, T 1 01 is the power age system similar to the one em-
ceivers. The complete schematic for transformer (for simplicity several ployed in the CTC47 chassis, which
this RCA CTC49 chassis can be windings were deleted from the illus- was derived from the circuits in the
found in the February Tekfax, Sche- tration) and S102 is the NORMAL/ CTC40 chassis. However, because
matic No. 1342. HIGH line switch. At "turn -on" the of the wider CRT deflection angle
resistance of temperature compen- used in the CTC49 chassis, a more
Power Supply sating thermistor RT1 is low and sophisticated means of correction is
Although the power supply utiliz- the degaussing current is high. As necessary to overcome side pin-
es a transformer, one side of the ac thermistor RT1 warms, its resist- cushion, the horizontal scan must
line is connected to the chassis. Its be increased when vertical scan is
dc outputs and their principal uses near the center of the raster. In
are as follows: R4
earlier RCA color -TV sets, this
The 220v source powers the kine DEGAUSSING
GEI4.
420
correction was accomplished by pas-
fEer,
drivers, Modules MAD. A half - VOWER NT I
sive components. Since the high -
wave rectifier and an RC -pi cir- voltage regulator of this chassis also
controls the scan width, side pin -
11
cuit are used in supplying this
filtered voltage. cushioning may be corrected by pro-
Four diodes in a bridge configu- viding a second input to the regula-
ration provide two additional Fig. 1-Simplified schematic of the automatic tor. This input is derived from the
power sources. One of these, us- degaussing circuit. vertical deflection circuits and proc-
FEBRUARY 1971, ELECTRONIC TECHNICIAN/DEALER 33
variations in supply voltage, ampli-
fier gain, etc., which would drasti-
cally change the output of a conven-
T401
HV Transformer
tional vertical -deflection circuit,
would have very little effect in the
Miller circuit because of the large
degenerative feedback.
0101 A schematic of the RCA CTC49
Vertical Output Transistor chassis vertical -output stage is
shown in Fig. 4 with a simplified
yoke circuit. The circuit configura-
-0102 tion is similar to a high -quality audio
Vertical Output Transistor
amplifier. The yoke itself is analo-
SCR 102 gous to a speaker voice coil, capac-
Commutating Rectifier
itor C419 to the coupling capacitor,
SOM 101
- High Voltage Quadrupler and R, equivalent to the total re-
SCR 101 sistance of the yoke and convergence
Trace Rectifier
circuits. The value of capacitor
C419 has been chosen to provide
Rear view of chassis showing components employed in the horizontal and vertical sweep circuits maximum energy transfer at the
of the RCA CTC49 color chassis. vertical scanning frequency. Feed-
back to the Miller capacitor is de-
essed by the circuit shown in Fig. 2. which is the result of the capacitance veloped across resistor R13, and ca-
To correct side pincushioning, it of the kinescope ultor (second pacitor C10 is a filter.
is only necessary to increase the for- anode) connection. During retrace, transistor Q3 is
ward bias of transistor Q402 when The amount of effect which this cut off, allowing its collector voltage
vertical scan is near the center of the sample from the quadrupler will to increase towards B+. The 65v
raster and decrease it when the ver- have on the pincushion amplifier zener diode, CR4, limits the maxi-
tical scan is near the top and bot- may be adjusted with potentiometer mum base bias of transistor Q101,
tom. One output from the vertical R428. The amplifier has been de- serving to limit yoke retrace current.
deflection system is fed to the base signed so that when brightness is set During scanning time, the bases of
of transistor Q402 by way of resis- for a barely visible raster and poten- transistors 0101 and 0102 are
tors R416 and R415 while another tiometer R428 is set to minimum driven progressively less positive at
arrives through resistor R417. These (CCW) there will be no pincushion. a linear rate. Conduction is through
samples of vertical deflection signal Potentiometer R428 is then adjusted transistor Q101 during most of the
are shaped into a parabolic wave- to correct the pincushioning, which retrace time and as the scan passes
form which reaches its maximum will appear when the brightness is from the top to the center of the ras-
positive potential at vertical mid- increased to maximum. ter. The voltage across capacitor
scan. Unlike conventional high -voltage C419 reaches its maximum at the
Two additional inputs from the power supplies, which rectify a posi- center of vertical scan (90° out of
horizontal deflection system are used tive pulse from the flyback trans- phase with the current), and during
to optimize this high -voltage regula- former with a half -wave rectifier, the the lower half of the scan capacitor
tion and pincushion correction. The CTC49 chassis uses a solid-state C419 discharges back through the
first of these is obtained from ter- quadrupler to produce high voltage. yoke and transistor Q102. This cur-
minal D (Fig. 3) of the high -voltage This reduces the required pulse am- rent increases at a linear rate, since
quadrupler through resistor R115, plitude from about 23kv to normal- the forward bias on the base of tran-
and reaches the base of transistor ly 6kv. The quadrupler itself is her- sistor 0102 is also increasing at a
0402 by way of resistors R426 and metically sealed and is not repair- linear rate.
R419. It allows the regulator system able. The diode connected between the
to "measure" the beam current and bases of transistors Q101 and 0102
more accurately regulate the high Vertical Deflection Circuits improves the switching characteris-
voltage. The vertical feedback circuit em- tics of the transistors at mid-scan.
The second input is obtained from ployed in the CTC49 chassis is Transistor Q102 has no bias as long
terminal C of the quadrupler and known as a "Miller run-down cir- as transistor Q101 is conducting.
reaches the base of transistor Q402 cuit." This circuit was seldom used Therefore, only slight voltage swings
by way of potentiometer R428. This until the advent of transistors be- are necessary to cut off transistor
input samples the high voltage by cause of its high gain requirements. Q101 and turn on transistor Q102
means of the capacitive voltage di- The Miller run-down circuit multi- at the center of the raster. If the di-
vider, made up of capacitor C426 plies the changing capacitance by a ode were shorted or bypassed, re-
and the capacitors in the quadrupler. factor equal to the gain of the ampli- verse bias would exist between the
It compensates for phase shift of the fiers without feedback, resulting in base and emitter of transistor Q102
side pincushion correction voltage, a very linear output. Many of the while transistor Q101 was conduct-
34 I ELECTRONIC TECHNICIAN/DEALER, FEBRUARY 1971
VERT
OUTPUT
V
4- C419
470,,F
R416
BRIGHT 82K
LIMITER R115 HV ADJUST
4 R411 T402
HV OUAD-o--1\A.7KAr--.
I
I
TERM 0 C4' 7
CONV
C109
C420
0082 R415 7 33
BOARD R426
.01 R419 68K
330K 330K 0401
R414 CR405 CR404
HV QUAD
I C306 _L c421 100K
.01
TERM C I .15
_l_ 0402
C42C =
C426 R428
.01
VERT 1 1 MEG C415
YOKE PIN T 5.8 ,F
ADJUST R417
82K
R412
J_ 270
CURRENT 33
TOP HALF R13 R413
OF RASTER (MAG) 82K
2.2
Fig. 2-Diagram of the side pincushion amplifier circuit. The high voltage regu ator also ontrols the scan width. The side pincushioning is corrected
conveniently by providing a second input to the regulator.
20 I kV
1120 LINE
IOW* ZERO BEAMI
F. 3-The solid-state High -Voltage Quadrupler (at left) produces
the high voltage. It is hermet cally sealed and not repairable.
77
BRIGHTNESS
FOCUS DIVIDER
LIMITER
VERTICAL R16
SIDE PIN ADJUST (R428)
PRE DRIVER 330
SIDE PIN AMP
Fig. 4-Schematic of the vertical -output stage
R'7
1530
with a simplified yoke circuit.
ing, and consequently there would