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ELECTRONIC TECHNICIAN CEALER SEPTEMBER 1971
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.
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-
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
AGC Modul IF Subcnas
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
'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
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
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.
EEr j; TOOT
RTC. Video Circuitry
sow /. 1.71-
The AGC module, No. 9-48 (Fig.
11) 00:05 9), employs very few components
because of monolithic construction
CON CRT FOCUS LEM) -the 221-45 video signal integrated
circuit. And the interval generation
of the reference level by zener di-
11III odes and associated circuitry elim-
.2114 inates the requirement for an AGC
OMIT OF WirEl NETWORK
To 11- AT
P OWER WIRY
SKOV The signal from the second de-
2110 US TM KS
240 tector is dc coupled to the AGC
CEOS .-OE/0V threshold detector, where it is com-
UMI pared to a reference level generated
in intervals. In the IC, this is 5v
with respect to ground. Since this
CESA is the level at which the sync tips
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
coincides with the signal sync pulse. OUTT
Thus, no sampling is accomplished
during scan time. Further, when- zv..-jel
ever an AGC gating pulse is pro- 1-.--
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-
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
trol voltage on the filter, there must 2
be a level difference between the 7 *m.
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
The filter control voltage is am- IL= Hi- OS
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
continued from page 39
video information is delayed so that
when the inverted noise pulse is
added to the delayed signal, it ar-
rives before and finishes after the
original noise pulse in the signal.
130 This causes complete cancellation
of the noise in the video.
Next month we will cover the col-
or processing circuits which employ
so Oyes three integrated -circuit packages
plugged into sockets for easier ser-
CLOCK MOVEMENTS vicing.
DIGITS RESETTABLE INDIVIDUALLY
Avooloble SO, 60 cy all voltages. AC. UL
approved motor, cord. One Yeor Goarontee.
Removes miniature soldered compo-
nents in seconds-without damage
Hollow tip fits over connection; vacuums all solder CAT GAME...
for easy removal of component. Leaves terminals
continued from page 45
and mounting holes clean. Then, with 360° contact,
it resolders faster, better than regular irons. Hand-
les miniature and standard components in PC circuit of sync separator tran-
Made in U.S.A.
boards and conventional wiring. Self-cleaning. All sistor TR9 to ensure noise -free
parts replaceable. 40 watts, 120-v. Standard tip sync.
Complete Line: Delay, Interval supplied, 5 other tip sizes available. Pays for itself.
and Cycle Timers, Digital Computers
$11.95 net East of the Rockies.
19. (d)-Located in the vertical
PENNWOOD NUMECHRON CO.
system's feedback loop, capaci-
Larger model available. See your distributor or write:
tor C76 and the adjacent 5.6K
7249 FRANKSTOWN AVS .
PITTSBURGH. PA 15201
ENTERPRISE DEVELOPMENT CORPORATION resistor form a low-pass filter,
5127 E. 65th St. Indianapolis, Ind. 46220 which is necessary to prevent
... for more details circle 178 on Reader Service Card ... for more details circle 114 on Reader Service Card
horizontal pulses from being
coupled back to the base of
8 PACK transistor TR15, where they
would upset the precise timing
of the oscillator-producing
8 Packs of chemicals with box of 5 precision tools
poor interlace. These horizontal
pulses are the result of "cross-
talk" between the horizontal
NEW Valve for easy insertion of extension tube and vertical deflection coils in
NEW Ultra Wissh formula for Color TV. 6 oz. aerosol TOOL
20. (a)-Capacitor C79 couples
negative -going sync pulses from
MODEL SC6A-8 MODEL HL6-8 MODEL HG6A-8
ULTRA WI SSH LUBRITE with MIRACLE BATH the collector of transistor TR9
with precision precision nut with precision
screwdrivers. driver. wrenches. ti to the base of transistor TR16
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FROM SARASOTA, FLORIDA PRODUCTS, INC
$ 8 88Ne\D I r. t EVERY
(the driver, being an emitter
follower, does not invert signal
phase), thus, negative -going
... for more details circle 142 on Reader Service Card sync pulses are fed to the input
of transistor TR17. The latter
inverts the pulses so that posi-
[CORNELL) ELECTRONICS COMPANY tive sync pulses are fed back to
4213N. UNIVERSITY AVE. SAN DIEGO CALIF. 92105 the P -type base of the NPN
Same Low Price * Bargain Tools normally OFF transistor
East or West Coast! * Transistor Tester
* Technician's Library
(TR15), triggering the oscilla-
OFFER tor ox. With C79 open, the ver-
ON ALL ORDERS
OVER $10.01:1 tical deflection system is free
SEND FOR FREE running.
NEW 48 PAGE How do you rate? Score five
BOXED COLOR CATALOG 25c
points for each correct answer -90
to 100 is excellent, 75 to 90 is good,
5 DAY MONEY * Dumont Picture Tubes FROM THIS LIST
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74 I ELECTRONIC TECHNICIAN/ DEALER, SEPTEMBER 1971
L901-chroma take -off coil S-85761 loop of No.24 aug. copper wire 91-2061 ZENITH
PL1-neon bulb 13AG-61 100-571 F203 -0.5a bel -I use 136-84
T201 -audio output xformer 95-2883 F204 -0.07a bel -fuse 136-90
Color TV Chassis
7202-vert output xformer 95-2915 SW205-master off switch 85-1260 25CC55
T203 -saturable reactor xformer 95-2881 CR220-HV tripler 212-104
T204 -deflection yoke 95-2880 CR1001-3.58MHz osc crystal 013-89
T205 -power xformer 95-2954 C401 -integrated circuit 22145
T206-horiz driver xformer 95-2895 C901 -integrated circuit 221-43
T207-horiz sweep xformer S-89430 C902 -integrated circuit 221-46
T208 -filament xformer 95-2953 C801-horiz thick film (use on 9.70 only) 223-4
F202 -heater fuse line 2%" minimum. C1001 -integrated circuit 221.42
C11 -1 -integrated circuit 221-48 .24V
ILIAD N 01(51
r-- 121-712 of
I CI. a PART Of NAT OF SOUND cm 11r RO) TEST POINTS
00011 05 *KT J203 ,PZO5 22S3
0217 OUTPUT r:4f. 2.11.12,1,(32025 050155 4TH
fgr 001 20 of 1(0.053 .
121-695 r j ISOW
0202 .01 an2CRYKALLT
oartfientleMASL21 229 2.226 CI PICTURE DETECTOR OUTPUT
VERT. BLANKER 121-695
CCI WAS POINT FOR CI ADJUST
BLANKER CRT IOCKET 39 V C2 WINO DETECTOR OUTPUT
. ,113;i7tISS WITH S. .2115 [LETO
tr. I I.F. A.S.C.
. o rrGT TES POINT MR 4TH I.P.
P ART 402 .60,0641 22
0203 2222 ri ..g. A .CC .
1 2 t250
121-744 02 .55 02 4,
, .. 0206**s.1. TURN COLOR THRESHOLD CONTROL
2ND VIDEO 11011222[SS 0205** cmv
RUT 121-743 a 4.4.4,....01=1