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ELECTRONIC TECHNICIAN CEALER SEPTEMBER 1971
TEKLAB REPORT
Exploring Zenith's
Titan 110 Color -TV Chassis
by Joseph Zauhar
Five plug-in modules employing plug-in
transistors and integrated circuits provide
fo easier and simpler servicing
As new color -TV receivers ap- that it has many useful features-
pear on the market, it is very obvi- not only for the customer, but the
ous that modular solid-state circuit- service technician as well. Their ad-
ry will soon dominate the color -TV justments are simplified with the use
field. As an example, Zenith has of new TINT, COLOR LEVEL, BRIGHT-
just introduced its first all solid-state NESS, CONTRAST and VERTICAL
color chassis, called the Titan 110, HOLD controls. By turning each con-
employing five modular circuits. trol until its red -line indicator is in
After reading the product re- the 12 o'clock position, a satisfac-
leases with great interest, we or- tory picture is obtained-or the con-
dered Zenith's Model C4787P con- trol can be adjusted to customized
sole color -TV set, employing the setting if they are desired. By re-
25CC55 chassis. Upon viewing this moving two screws (Fig. 1), the
TV set from the front, we noted speaker can be removed to provide
access to the convergence board for
up -front adjustments.
The 25CC55 chassis that we ex-
amined (Fig. 2) is of all solid-state
design similar to last year's 40BC50
chassis. But since that chassis was
never produced in commercial
quantities, the 25CC55 can be con-
sidered a new chassis.
This chassis employs five plug-in
integrated circuits and five Dura-
Modules (Fig. 3). These snap -in
modules provide both a carrier and
interconnecting system for a num-
ber of solid-state circuits. The tran-
sistors and integrated circuits plug
into sockets on the modules, thus
eliminating the need to remove the
modules for the replacement or test-
ing of components.
The CRT socket (Fig. 4) incor-
Zenith's Model C4787P color -TV Set E m)loying the 25CC55 chassis. porates several 1K resistors at the
pin terminals of the CRT elements
for improved arc protection. Should
SEPTEMBER 1971, ELECTRONIC TECHNICIAN/DEALER 35
an arc occur in the picture tube, its
energy should be dissipated across
the resistor near the source of the
arc. Spark gaps are also employed
at each end of the resistors to dis-
sipate any energy that is not fully
dissipated by the resistors.
Power Supply
The power supply employed in
this chassis is quite similar to the
supply used in the 40BC50 chassis VOLUME Contro
but with a few significant changes.
A simplified schematic of this pow-
er supply is shown in Fig. 5. Voltage
feedback is not utilized and a zener COLOR LEVEL
diode is used as a voltage reference. Control
A zener diode (Z1) is used in the
input and transistor TR1 acts as a
constant voltage generator. The
emitter of TR1 is a fixed voltage TINT AUTO TINT
source (E 1 ), and the current has to GUARD Switch
be amplified to supply enough cur-
rent (up to 15ma base current for a
450ma output) to transistor TR3.
Transistor TR2 is the second cur-
rent amplifier.
Transistors TR2 and TR3 have a
minimum current gain of 30. With
both current gains multiplied, the
minimum total gain will be 900. If
the maximum current through TR3 Convergent
is equal to 450ma, then with a gain Panel
of 900 the base current drawn from
TR2 will be 450/900 or 0.5ma. Fig. 1-After removing two screws, the speaker cai be removed to expose the cInvergence board
This load will reflect back to the for up -front adjustments.
voltage divider, located at the emit-
ter lead of TR1, which passes a
minimum current of 10ma. This
means that the maximum output .ubcarrier Regen Module
load will offset the voltage of the di- Sound Modu e
vider by no more than 5 percent, or Video Output
Vertical Mcc ule Transistors
6v, because of the 120ft, 22w re-
sistor in parallel with TR3 and the
gain of TR2 and TR3.
An "instant on" feature is em-
ployed in this chassis-requiring the
use of an additional transformer
which supplies only the filament
voltage for the CRT (approximately
4.8v when the receiver is turned
on). A winding in the main power
transformer-which is connected in
series with the additional transform-
er-adds approximately 1.5v to the
CRT filament source to obtain the Honzont 31 Module Shrorna Module
6.3v required when the TV set is
used.
AGC Modul IF Subcnas
Horizontal Circuitry
We found the horizontal circuitry Fig. 2-Zenith's 25CC55 fully solid-s:ate color -Ii ciassis features a unique sys-.em of five inte-
similar to that employed in the grated circuits and plug-in Jura-Modufes.
36 ELECTRONIC TECHNICIAN/ DEALER, SEPTEMBER 1971
Fig. 4-The CRT socket employs several re-
sistors and spark gaps at the pin terminals for
arc protection.
't/ 1 It t -it"
Fig. 3-Five snap -in modules provide both a carrier and interconnecting system for a number of Fig. 5-Simplified schematic of the 25CC55
solid-state circuits. chassis power supply having a constant -current
transistor input. Courtesy of Zenith Radio
Corp.
40BC50 chassis. Although some base from transformer T206. This occurs when the horizontal output
capacitive values in the output cir- "loads" the primary winding of the transistor is in saturation.
cuitry were changed to optimize per- flyback transformer, causing in- The primary winding of the hori-
formance, the circuit operation is creased current flow until the posi- zontal transformer and the yoke are
identical. To improve the horizontal tive going square wave at the base tuned to the retrace time intervals.
phase lock, the AFC transistor's for- of Q216 swings negative. The In transistor sets, this is usually
ward bias circuitry was modified. same current flow also occurs in the
In some TV sets, part of the hori- yoke and causes the CRT beam to
zontal sweep circuitry is mounted on be deflected from center to edge.
a module assembly, Part No. 9-57 When this occurs, transistor
(Fig. 6), as used in the chassis for Q216 is completely cut off and the
our report, but an alternate Part No. magnetic field in the flyback col-
9-70 is also used with the sweep cir- lapses. The collapse causes a posi-
cuitry incorporated on a substrate tive high voltage of very short dura-
(thick film) soldered to the module. tion to be generated and applied to
The horizontal output stage, flyback, the collector circuit of Q216 (re-
damper, focus and related circuits trace interval). The build up and
are all chassis mounted (Fig. 7). collapse of voltage (about 1 kv)
This chassis contains no high -volt- takes approximately 12/.6. Since
age adjustment. High -voltage regu- this is a tuned circuit, the positive
lation is accomplished by regulating half cycle then begins to swing neg-
the B+ and using a flyback that is ative, but damper diode CR217 now
tuned to the fifth harmonic of the becomes forward biased and this
pulse frequency. This provides in- causes a "reverse" current flow
herent regulation without a separate through the yoke. The reverse cur-
regulatory stage. rent drives the beam spot through
The horizontal output transistor, the first half of the horizontal scan.
0216 (Fig. 8), is driven into satu- Fig. 6-The horizontal sweep module, Part No.
As previously stated, the beam is 9-57, employs the horizontal AFC, oscillator,
ration by the positive -going portion scanned from center to right side sawtooth shaper and horizontal -driver tran-
of the square wave coupled to its of the CRT by the yoke current that sistors.
SEPTEMBER 1971, ELECTRONIC TECHNICIAN/DEALER 37
about 12i.ts or about 41.5kHz. Com- the tertiary (third winding), high - output transistor is operated as a
mon practice in the past has been voltage rectifier and the leads, res- switch in this TV set and solid-state
to wind the third winding of the onates at six times the frequency of regulators have not been developed
horizontal transformer so that its the frequency corresponding to the with the reliability needed, fifth har-
leakage inductance, the capacity of retrace time. Since the horizontal monic tuning is used in the tertiary
winding. This is accomplished by
reducing the capacitance.
Since the TV set contains voltage
tripler circuitry, it is able to func-
tion with a smaller tertiary winding.
Only 8.5kv pulses is required to ob-
tain 25kv. By being tuned to this
upper harmonic, about 200kHz, the
121-831 conduction time of the high -voltage
Horizontal Output
Transistor rectifier is increased, lowering the
effective impedance of the load.
This is said to give much better
high -voltage regulation than un-
tuned flybacks or third -harmonic
tuned flyback circuits.
High Voltage The flyback circuit is also used as
Tripler a source of current for the second
grids in the CRT-diode CR219,
with associated filters and bleeders
being used to rectify a portion of the
1 kv pulse generated by the flyback
retrace. And the 250v supply for
the other CRT grids and video out-
Bleeder Resistor put circuits is obtained by adding a
small winding on the flyback, and
rectifying and filtering the pulse
with diode CR221, and capacitors
C257 and C258. The -40v tuner
0 bias supply is also obtained from the
flyback at one of the convergence
Fig. 7-The horizontal output stage, flyback, damper, focus and related circuits are chassis mounted.
windings. This is rectified and fil-
tered with diode CR218 and capaci-
tors R346 and C351.
-ov 0
EEr j; TOOT
RTC. Video Circuitry
sow /. 1.71-
Mt Otwmi
The AGC module, No. 9-48 (Fig.
RED
cam! 01.1E0ER
11) 00:05 9), employs very few components
0216
21-831 omPur
because of monolithic construction
HORIZ. OUTPUT
CON CRT FOCUS LEM) -the 221-45 video signal integrated
SFr
tan
AMS C0.2TROL
circuit. And the interval generation
Lee at
%ff..; tais
of the reference level by zener di-
3 UV
11III odes and associated circuitry elim-
RIMINITNESS
LIMITER
T FOCUS
.2114 inates the requirement for an AGC
OMIT OF WirEl NETWORK
IHS
Lh 34.0
level control.
"cti WWi
To 11- AT
P OWER WIRY
SKOV The signal from the second de-
:1"
+.1r. :fg:
2110 US TM KS
240 tector is dc coupled to the AGC
CEOS .-OE/0V threshold detector, where it is com-
41/ 1I
MEG CRa
UMI pared to a reference level generated
in intervals. In the IC, this is 5v
with respect to ground. Since this
+25000
CESA is the level at which the sync tips
)00v I-
will be clamped, the detector output
can be varied by the zero -carrier
level. In current chassis, zero -carrier
Fig. B-Schematic of the horizontal output circuits used in the 25CC55 chassis. Courtesy of Zenith
corresponds to 8.5v to 9v at the first
Radio Corp. video stage emitter, resulting in a
38 ELECTRONIC TECHNICIAN, DEALER, SEPTEMBER 1971
3.5v to 3.75v p -p output for 90 per- conventional discrete circuits, the adjustable clamp voltage.
cent modulated signals. AGC voltage is fed initially to the While gating the AGC compara-
The AGC comparator is "gated" 1F amplifier and then, after a suit- tor with sync pulses limits the pe-
so that rapid alternating signals can able delay, applied to the RF am- riod during which the system is sus-
be utilized with good noise immu- plifier. The delay point is adjust- ceptible to impulse noise to merely
nity. However, two "gates" are used. able by an external control, and 20 percent of the signal time, addi-
To charge or discharge the AGC positive -going or negative -going RF tional techniques are employed for
filter, two inputs to the comparator control voltages are available. When improved noise performance.
must be present. As with conven- the sync tip level at the detector is When the noise pulse amplitude
tional circuits, the line flyback pulse below the required threshold level exceeds a certain threshold level be-
must be present but additionally, the (i.e., very weak signals), the filter low sync tips, a noise pulse is de-
negative going separated sync pulse voltage is maintained at the correct veloped. This pulse is amplified,
from the input video signal must be level to ensure maximum signal gain "stretched" (i.e., increased in width)
present. Coincidence of the two of the RF and IF systems (for max- and inverted. Simultaneously, the
pulses will result in AGC action if imum sensitivity) by an externally continued on page 74
the detected signal level changes.
If, however, the line oscillator is
out of synchronization, no AGC ac-
tion will occur until the line pulse :114 SYNC
II
5 SYtk
coincides with the signal sync pulse. OUTT
IN
T.) ;f2.f8f..1.fo
Thus, no sampling is accomplished
during scan time. Further, when- zv..-jel
,?,1
ever an AGC gating pulse is pro- 1-.--
717
duced by coincidence of the line fly-
1.0 40' 221 45
back pulse and the separated sync,
not only is the AGC comparator ac-
1-470,
tivated but a constant -current dis- ...4.:0'0UTPUT
charge of the AGC filter occurs. rf.
This means that to maintain a con- SSEWItv2L11,"__
viDEO PROCESS011 MODULE
I
trol voltage on the filter, there must 2
be a level difference between the 7 *m.
O.za Sul.,
!4,11,0C
video detector output and the ref- ..zv
erence voltage. a02- ". -40v
The discharge current is about
1.7ma and is always constant while Fig. 9-The AGC module employs very few componeots due to monolithic construction techniques.
gating action occurs. The level dif- Courtesy of Zenith Radio Corp.
ference between sync tips and the
reference voltage will replenish the
charge lost by the filter capacitor
and maintain a constant voltage on =41 1:11'
the capacitor for a given signal level.
If the signal strength at the de-
tector increases (changing the level
between sync tips and the reference
voltage) additional discharge cur-
rent will be provided by the AGC
comparator to increase the filter
capacitor voltage. This control volt- EF
age will reduce the RF and IF gain -11141.11
to keep the detector level constant
as the AGC comparator again
equals the discharge current-but at
a new control voltage level. The de-
tector level is therefore virtually
constant for all signal strengths and
control voltages.
The filter control voltage is am- IL= Hi- OS
T
plified and "buffered" (a circuit
used to prevent interaction between
two stages) before application to Fig. 10-Block diagram of the circuits employed in the video processor module. Courtesy of Ze-
the IF and RF amplifiers. As with nith Radio Corp.
SEPTEMBER 1971. ELECTRONIC TECHNICIAN/ DEALER ; 39
An Alternate Solution
by Phillip Dahlen
Sometimes you just can't use a roof antenna
Just about all electronic techni- repercussions from their landlord As an alternate solution, Channel
cians will agree that a good roof an- should they attempt a roof installa- Master has developed a transistor-
tenna is a must if you are to obtain tion, or loss of the antenna should ized indoor antenna for use on top
the best possible, interference -free they move in the near future. For of a TV set. The antenna has con-
color -TV signal. There are, how- similar reasons, it may not be feasi- trols for rotating the UHF antenna,
ever occasions when you may en- ble to make an attic installation (a switching the amplifier between
counter customers who either fear second best installation). UHF and VHF functions, and tun -
The complete sol-
id-state amplifier
is housed within
the base of the
antenna.
Channel Master's transistorized Super Chroma
82 antenna contains controls for rotating the
UHF antenna, switching the amplifier between
UHF and VHF functions, and tuning the
circuitry for best reception.
On one channel, the rabbit ears built into
the TV set are unable to adequately receive
the high -quality signal transmitted by the
station.
By substituting the transistorized antenna
A shielded cable is used between the amplifier for the rabbit ears (and operating its elements
and the UHF/VHF splitter at the back of the at the same length as the rabbit ears), a
TV set-thus preventing feedback between the much better picture is received from the
input and output of the antenna amplifier. same station.
40 I ELECTRONIC TECHNICIAN/DEALER, SEPTEMBER 1971
ing the circuitry for best reception. picture of the living room TV set, where TV sets are an adequate dis-
To prevent feedback between the about 50 ft away. Retuning the am- tance apart.
input and output of the antenna plifier completely eliminated this We have been quite pleased with
amplifier, a shielded cable is used interference. Whatever its cause, the transistorized antenna, and
between the amplifier and the UHF/ this interference is certainly not a hope to continue using it until there
VHF splitter at the back of the TV problem that will be experienced in is time to make an additional con-
set. a home having but one TV set, or nection to our roof antenna.
Although accurate specifications
can always be written so that they
sound impressive, the proof really
comes in seeing how the product ac-
tually performs. It was therefore de-
cided to take the antenna home -10
to 12 miles from a hill where all of
Duluth's TV transmitters are lo-
cated.
The house that we purchased last
spring came with a large directional
antenna with a twin -lead to the liv-
ing room. Unfortunately, there has
never been enough free time avail- Reception with the transistorized antenna is
able to run another wire to the bed- improved by changing the TV set to another
channel.
room for our second color -TV set
(not that TV programs are watched
much in either location). And by
using merely the rabbit ears built in-
to the second TV set, we have never
been able to obtain ideal color -TV
reception. However, we have found
that a far more satisfactory picture
can be obtained by substituting the
transistorized antenna. As shown on
this month's cover, we were also
able to obtain satisfactory color -TV
reception in the living room when
substituting the transistorized anten- Using the transistorized antenna results in a
na for the roof antenna. slight interference pattern on the other
Only one slight problem was en- TV set.
countered when using the transistor-
ized antenna on the second TV set.
(This problem may have resulted
from some minor defect in the par-
ticular sample used, had something
to do with the design of our second
TV set, or been the result of using
unshielded lead-in wire from the an-
tenna on the roof above to the TV
set in the living,..toom.) Whatever
the cause, we discovered that when
the second TV set was turned off,
certain settings of the antenna's am-
No interference pattern can be seen on the
plifier (while connected to that set) other TV set after retuning the transistorized
would produce beat patterns in the antenna.
SEPTEMBER 1971, ELECTRONIC TECHNICIAN/DEALER 41
The CAT Game -- Part II (emitter circuit of audio -output
transistor TR14).
(a) picture okay, no sound
by Lambert C. Huneault (b) no picture, no sound
(c) picture okay, distorted
sound
C.A.T.-Circuit Analysis and Troubleshooting-is the name of the game. (d) little noticeable effect
The first quiz (October 1969 issue of ELECTRONIC TECHNICIAN/ 9. Capacitor C76 shorts (above
vertical oscillator transistor
DEALER) dealt with a vacuum -tube TV set. Now, for the sake of variety TR15).
and to bring your troubleshooting up-to-date, this second game is based (a) non-linear vertical deflec-
on the schematic diagram of a solid-state TV set. tion
(b) picture rolling vertically
(c) no vertical deflection
The following 20 multiple-choice AGC Gate transistor TR8). (bright line only, at cen-
questions test your understanding of (a) no raster, sound okay ter)
circuit functions and your ability to (b) no picture, sound and ras- (d) picture shrinks about 3 in.
predict the symptoms expected from ter normal from the bottom
component failures. At the end of (c) picture snowy, sound okay 10. Capacitor C100 opens (collec-
this question section, answers are (d) "overloaded picture," i.e., tor circuit of horizontal output
given along with explanations which, picture has excessive con- transistor TR21).
we hope, will shed some light on trast, or, depending on sig- (a) no raster
transistor circuit behavior and gen- nal strength, may even (b) raster lacks width
eral transistor TV theory. turn "negative" (white - (c) no noticeable effect
We hope you enjoy the game. . . . and -gray scrambled pic- (d) horizontal sweep badly
Good luck! ture) with buzz in the non-linear
sound 11. Capacitor C110 shorts (located
Questions 5. The 2.2K resistor opens in the to the right of high -voltage rec-
1. Horizontal damper diode X12 base circuit of the video -output tifier tube V1).
opens. There will be . . . transistor. (a) raster blooming and out of
(a) no raster (a) no pictire, no sound focus
(b) white vertical bars on left (b) no picture, with sound (b) retrace lines visible through
side of raster (c) no raster the picture
(c) narrow raster (shrinks in (d) "white crushing" (no in- (c) raster okay, no picture
from the sides) termediate contrast val- (blank white screen)
(d) little noticeable effect ues); most of the picture (d) no raster
2. Capacitor C86 opens (located is uniform white, with 12. Electrolytic capacitor C78 shorts
near horizontal phase detector only the very darkest pic- (in collector circuit of vertical
diodes). ture areas showing as oscillator transistor TR15).
(a) no raster dark gray. (a) no vertical deflection
(b) picture breaks into diag- 6. Damper diode X12 shorts. (b) picture rolls vertically
onal bars (a) picture very non-linear, (c) picture has excessive height
(c) raster okay, no picture horizontally (and non-linear)
(blank white screen) (b) no raster (d) vertical sweep non-linear
(d) piecrust (geartooth) dis- (c) raster slightly narrow, with and lacks height
tortion in picture white vertical bars on left 13. Capacitor C75 opens (base cir-
3. The 33K resistor opens in the side cuit of vertical oscillator).
base circuit of the video -output (d) narrow raster (lacks width) (a) picture rolls (no vertical
transistor. 7. The 100K resistor opens in the sync)
(a) no raster base circuit of Noise Gate Tran- (b) no vertical deflection
(b) no picture, sound and ras- sistor TRIO. (c) non-linear vertical sweep
ter normal (a) picture snowy (d) raster lacks height
(c) washed out picture with (b) picture okay, noise in the 14. Capacitor C83 opens (located
only bright highlights vis- sound above the vertical deflection
ible on a gray background (c) no sync (picture rolls ver- coil).
(d) little noticeable effect tically and slips horizon- (a) vertical retrace lines visible
4. Capacitor C49 opens (near tally) through the picture at low -
(d) picture okay on strong, contrast and/or high -
The author is supervisor of the noise -free signals, but sync brightness levels
Electronics Dept., Audio Retraining unstable on weak, noisy (b) no vertical deflection
Div., St. Clair College of Applied Arts signals (c) no raster (not even a bright
and Technology, Windsor, Ontario. 8. Electrolytic capacitor C74 shorts horizontal line)
42 I
ELECTRONIC TECHNICIAN/DEALER, SEPTEMBER 1971
USI.S. TUNER
uw I.E.ASSEMBLY nR
LIAS PART IPS 150-741 TR 3 TR4 TR5 TR6
121-510 121-600 121-447 , 11
SEE Wit CiOr.5 "-- 121-445
3RD I.F, VIDEO NOISE GATE VIDEO
15.4 cw..14. 2.4
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