Set-up arrangement for a color television receiver

A service switch to permit set-up adjustment of a color image reproducing kinescope in a color television receiver. The receiver comprises a horizontal deflection circuit for providing a periodic horizontal deflection signal having a frequency synchronized by a sync signal derived from a composite color video signal, and means for deriving a receiver operating voltage from the periodic signal of a magnitude dependent upon the frequency of the periodic signal. The switch has "normal" and "service" positions, and is coupled to respective direct voltage control terminals of luminance and chrominance channels and a vertical deflection circuit of the receiver. In the "service" position, the switch renders the luminance and chrominance channels inoperative to couple signals, and vertical scanning is disabled, to permit set-up adjustment of the kinescope. The sync signal is derived independent of the condition of the chrominance and luminance channels, and is coupled to the horizontal deflection circuit independent of the position of the switch, so that the derived voltage exhibits substantially the same magnitude in both "normal" and "service" positions.

The present invention relates to color television receivers and, in 
particular, to apparatus for facilitating the set-up and servicing of a 
color kinescope included in such receivers. 
Set-up of a color kinescope entails color temperature adjustments among a 
number of other adjustments. The color temperature adjustment takes into 
account the differences of the cathode emissions of the several electron 
beam producing guns of the kinescope and the differences in the 
efficiencies of the several phosphors of the kinescope. The color 
temperature adjustment typically involves adjusting direct control 
voltages applied between cathodes and grids of the kinescope and the AC 
gain of the kinescope drivers such that white information is reproduced 
with the proper color temperature at all brightness levels between minimum 
and maximum white, with the maximum white level being produced at the 
highest achievable level of brightness consistent with good image clarity. 
Service switch arrangements included in color television receivers are 
known which provide a convenient means for factory and service personnel 
to make adjustments without the need for additional equipment. Typically, 
service switch arrangements provide "normal" and "service" positions. When 
the service switch arrangement is in the "normal" position, the receiver 
operates to couple video signals to the kinescope for normal image 
viewing. 
When the service switch is in the "service" position, the vertical 
deflection circuits are disabled and the chrominance and luminance signals 
are decoupled from the kinescope so that the kinescope is in a quiescent 
operating condition. The direct control signals coupled to the grids (or 
cathodes) of each gun are gradually controlled until that gun produces a 
barely visible, narrow horizontal line on the kinescope. When all three 
guns have been so energized, the line will appear, from a suitable 
distance, as a white line of low brightness level. 
Various service switch arrangements are described in the following U.S. 
patents assigned to the same assignee as the present invention: U.S. Pat. 
No. 3,114,796 (J. Stark, Jr. et al.); U.S. Pat. No. 3,270,125 (G. E. Kelly 
et al.); U.S. Pat. No. 3,461,225 (P. E. Crookshanks et al.); U.S. Pat. No. 
3,525,801 (D. H. Willis); U.S. Pat. No. 3,820,155 (D. L. Neal); and U.S. 
Pat. No. 3,959,811 (R. L. Shanley, II). 
When one or more unregulated or partially regulated operating voltages for 
a color television receiver are derived from horizontal output circuitry 
of a horizontal deflection stage of the receiver, particular problems are 
encountered in providing an accurate set-up adjustment. Typically, such 
voltages are ultimately derived from the oscillatory output signal of a 
horizontal oscillator included in the horizontal deflection stage. The 
magnitudes of such voltages are determined in part by the frequency of 
oscillation of the horizontal oscillator, which in turn is stabilized by a 
synchronizing (sync) signal derived from a received composite video 
signal. In the absence of the sync signal, the oscillator frequency is not 
stabilized and tends to vary, thereby producing variations in the derived 
receiver operating potentials. 
In the service or adjustment mode of operation of such a color television 
receiver system, it is desirable to provide accurately simulated quiescent 
operating conditions in order to facilitate accurate set-up of the color 
receiver. Furthermore, it is desirable that the service switch control the 
various portions of the receiver with which it is coupled by direct (DC) 
control signal connections rather than by alternating (AC) control signal 
connections to minimize stray signal pick-up and other problems associated 
with long leads coupling alternating signals. 
An additional problem is encountered in the design of "service" set-up 
arrangements for color temperature adjustment of receivers of the type 
including an auxiliary (reserve) blanking circuit. One such circuit, which 
serves to inhibit kinescope operation during the vertical 
retrace-horizontal trace interval to thereby inhibit the formation of 
disconcerting horizontal trace lines, is described in U.S. Pat. No. 
3,984,864 granted to D. H. Willis and assigned to the same assignee as the 
present invention. When using such an arrangement, provision should be 
made to insure that such auxiliary blanking does not adversely affect the 
set-up procedure. 
In accordance with the present invention, a control arrangement is provided 
in a system for processing a composite color video signal containing 
chrominance, luminance and synchronizing signal components. The system 
includes chrominance and luminance channels for processing the chrominance 
and luminance components, a color image reproducing device having plural 
color producing electron beam apparatus responsive to chrominance and 
luminance signals coupled via the chrominance and luminance channels, and 
a deflection circuit associated with the electron beam apparatus for 
providing horizontal and vertical scanning of the reproducing device. The 
deflection circuit includes means for providing a periodic signal having 
time intervals representative of image trace and retrace intervals and a 
frequency synchronized by a sychronizing input signal applied thereto. A 
receiver operating supply voltage of a magnitude dependent upon the 
frequency of the periodic signal is derived from the periodic signal. A 
switch coupled to a direct voltage control terminal of each of the 
chrominance and luminance channels and the deflection circuit is also 
included. A first position of the switch renders the chrominance and 
luminance channels and the deflection circuit normally operative in a 
normal mode of operation of the system. A second position of the switch 
renders the chrominance and luminance channels inoperative to couple the 
chrominance and luminance components, and renders the deflection circuit 
inoperative to provide scanning of the image reproducing device in one 
direction, thereby permitting adjustment of the device in a service mode 
of operation. A signal separator operative independent of the chrominance 
and luminance channels serves to separate the synchronizing component from 
the composite video signal. A coupling circuit supplies the separated 
synchronizing component to the periodic signal deriving means as the 
synchronizing signal input independent of the position of the switch, 
whereby the derived receiver operating supply voltage exhibits 
substantially the same magnitude during both the normal and service modes.

In the following description it will be helpful to concurrently refer to 
FIGS. 1a and 1b which are parts of the same arrangement. 
In FIGS. 1a and 1b, there is shown a color television receiver including a 
video processing unit 12 for receiving from an antenna 10 radio frequency 
(RF) signals and for translating these signals through an intermediate 
frequency (IF) amplifying and detecting portion (not shown) to form a 
composite video signal. The composite video signal comprises chrominance, 
luminance and synchronizing signal components. 
A frequency selection unit 13 selectively couples the chrominance component 
to a chrominance channel 14, including a chrominance processing unit 16 
for processing the chrominance component to derive R-Y, B-Y and G-Y color 
difference signals. A viewer adjustable color control potentiometer 90 
serves to adjust the signal gain of chrominance unit 16 and thereby the 
amplitude of signals processed by unit 16. The color difference signals 
are coupled to respective inputs of kinescope driver stages 18a, 18b and 
18c of a kinescope driver 20. The kinescope driver stages combine the R-Y, 
B-Y and G-Y color difference signals with a luminance output signal, Y, of 
a luminance channel 22 to derive R, B and G color signals. 
The R, B and G color signals are respectively applied to cathodes of the 
three electron guns of kinescope 38. Each gun, for example, comprises a 
cathode, a control grid and a screen grid to develop and accelerate an 
electron beam. Focus and ultor electrodes are also provided. Direct bias 
control voltages are coupled to the control grids from a bias control unit 
40, and direct screen control voltages are coupled to the screen grids 
from screen control unit 42 to permit adjustment of the cut-off point of 
each gun. 
The illustrated kinescope driver stages 18a, 18b and 18c are of the type 
described in U.S. Pat. No. 3,970,895 granted to D. H. Willis and assigned 
to the same assignee as the present invention. Since stages 18a, 18b and 
18c are similar, the following brief description of stage 18c applies to 
stages 18a and 18b as well. 
Stage 18c comprises an NPN amplifier transistor 24c and an NPN keyed 
clamping transistor 26c arranged in feedback relation as shown. A +210 
volt source provides an operating voltage for stage 18c. The R-Y color 
difference signal is coupled to a base electrode of transistor 24c through 
a coupling capacitor 34c, the luminance output signal Y from luminance 
channel 22 is coupled to an emitter electrode of transistor 24c via a 
variable drive control resistor 28c, and periodic keying signals are 
applied to an emitter electrode of transistor 26c from a keying stage 130. 
Luminance and keying signals are similarly applied to corresponding inputs 
of driver stages 18a and 18b. 
Transistor 24c serves to combine and amplify the Y and R-Y signals to 
derive the color signal R at the collector output of transistor 24c. 
Variable resistor 28c is adjustable to control the gain of stage 18c. 
Capacitor 34c and transistor 26c form a keyed clamping circuit for 
maintaining the voltage developed at the emitter of transistor 24c 
substantially constant and independent of the direct current conditions of 
chrominance processing unit 16 and the base-to-emitter voltage variations 
of transistor 24c. The clamping action occurs when transistor 26c is 
rendered conductive in response to a keying pulse generated by keying 
circuit 130 during the horizontal flyback (retrace) interval. 
The output of video processing unit 12 is also coupled to a sync separator 
60 for deriving positive periodic line sync pulses from the video signal 
independent of the operation of the chrominance and luminance channels. 
The derived sync pulses are in phase with and correspond to the sync 
component of the video signal, and are coupled to a horizontal deflection 
stage including a horizontal oscillator 62 and horizontal signal 
processing circuits 64, and to a vertical deflection stage including a 
vertical oscillator 72 and vertical signal processing circuits 74. 
Periodic vertical deflection and vertical blanking signals provided by 
vertical signal processing unit 74 are coupled to vertical deflection 
windings of kinescope 38 and to luminance channel 22, respectively. Output 
signals from horizontal signal processing unit 64 are applied to a 
horizontal flyback transformer 76 to derive horizontal blanking, 
horizontal deflection and horizontal flyback signals. The horizontal 
deflection signals are coupled to horizontal deflection windings of 
kinescope 38, and the horizontal blanking signals are coupled to luminance 
channel 22. 
Positive horizontal flyback signals occuring during the horizontal sync or 
retrace interval of the video signal are coupled to a high voltage unit 
(e.g., voltage tripler) 78, which provides high operating voltages for the 
ultor and focus electrodes of kinescope 38, and to keying circuit 130 of 
luminance channel 22. 
Keying circuit 130 generates negative-going periodic keying signals during 
the horizontal retrace interval in response to and substantially 
coincident with negative-going horizontal flyback signals. The keying 
signals control the operation of the keyed bias transistors (e.g., 26c) of 
the kinescope driver stages during the horizontal retrace interval as 
described in U.S. Pat. No. 3,970,895. 
The horizontal flyback transformer 76 also provides voltages from which 
rectified unregulated, DC receiver operating voltages are developed. In 
this example, the unregulated operating voltage supply (+210 volts) for 
the kinescope driver stages is developed from a voltage produced by a 
tapped secondary winding of horizontal flyback transformer 76. 
Luminance channel 22 includes a luminance signal processing unit 44 for 
amplifying and otherwise processing the luminance component of the 
composite video signal to provide a "sync tips positive" luminance output 
signal in this example. The luminance component from unit 44 comprises 
periodic blanking pulses and signal portions representing image 
information disposed between the blanking pulses. The blanking pulses are 
formed by a pedestal level upon which are imposed sync pulses. 
The luminance component from the output of unit 44 is coupled to a keyed 
blanking level clamp circuit comprising a coupling capacitor 104 and a PNP 
clamp transistor 110. Periodic keying signals from keying unit 130 are 
combined with sync signals from sync separator 60 at a base electrode of 
transistor 110 to form a switching signal for controlling the clamping 
(conduction) intervals of clamp transistor 110. Clamp transistor 110 
conducts periodically to clamp the luminance signal in response to the 
minimum amplitude level of the switching signal. When clamp transistor 110 
conducts, the luminance signal coupled via capacitor 104 is clamped to a 
voltage then appearing on the base of transistor 110. This voltage 
represents a blanking reference level corresponding to a black tone of an 
image. 
Positive periodic horizontal and vertical blanking pulses, with time 
durations respectively corresponding to horizontal and vertical retrace 
intervals, are combined and amplitude limited by a blanking unit 160. The 
combined blanking signals are coupled to a base electrode of a PNP 
luminance amplifier transistor 105 where the combined blanking signal is 
summed with the clamped luminance signal to insure that kinescope 38 is 
substantially cut-off during the horizontal and vertical retrace 
intervals. Transistor 105 provides an amplified, clamped luminance signal 
Y to kinescope driver stages 18a, 18b and 18c. 
The output of keying unit 130 is also coupled to an auxiliary blanking unit 
145 to provide an auxiliary or reserve periodic blanking pulse during each 
vertical retrace-horizontal trace interval to insure that kinescope 38 is 
cut-off, so that disconcerting horizontal trace lines are not visible 
during this interval. Keying unit 130 and auxilary blanking unit 145 can 
be of the type described in aforementioned U.S. Pat. No. 3,984,864 of D. 
H. Willis. 
Additional control of clamp transistor 110 is accomplished by a brightness 
control variable resistor 112. Variable resistor 112 represents a manually 
adjustable, viewer operated control to vary the conduction of clamp 
transistor 110 and to thereby obtain a desired level of image brightness. 
Briefly, variable resistor 112 serves to adjust the bias and therefore the 
level of conduction and clamping voltage of keyed clamp transistor 110. 
Adjustment of resistor 112 between the minimum (MIN) and maximum (MAX) 
positions varies the blanking (or black) level of the luminance signal, 
and thereby image brightness from a minimum to a maximum level. The 
brightness control function (including the circuit portion designated 
generally as 100) is described in greater detail in co-pending U.S. patent 
application, Ser. No. 715,851, entitled "Brightness Control Apparatus", 
filed Aug. 19, 1976, in the name of M. N. Norman and assigned to the same 
assignee as the present invention. 
A two-position service switch 82 having two sets of electrically isolated 
poles and "normal" and "service" positions facilitates initial adjustment 
of receiver operating conditions. The receiver operates normally in the 
"normal" position. When in the "service" position, service switch 82 
permits color temperature adjustments of kinescope 38. 
A first set of poles includes poles 84a, 86a and 88a. Pole 84a is directly 
connected to a lower terminal of brightness control resistor 112, to a 
lower terminal of color control potentiometer 90 via a resistor 93, and to 
a source of positive direct voltage (+22 volts) via a resistor 92. Pole 
86a is connected to a point of reference potential (e.g., ground), and 
pole 88a is connected to a control input of auxiliary blanking unit 145. A 
second set of poles includes poles 84b, 86b and 88b. No connection is made 
to pole 84b in this example. Pole 86b is connected to a source of negative 
direct voltage (-40 volts), and pole 88b is connected to a control input 
of vertical oscillator 72. 
In the "normal" position, poles 84a and 86a are connected together via a 
negligible impedance so that pole 84a and therefore the junction of 
resistors 92 and 93 are at ground potential. Color control potentiometer 
90 and brightness control resistor 112 operate in normal fashion, and 
chrominance and luminance signals are processed normally by the 
chrominance and luminance channels, as discussed earlier. 
In the "service" position, poles 86b and 88b are connected together through 
a negligible impedance, so that a negative voltage (-40 volts) appears at 
pole 88b and is coupled to the control input of vertical oscillator 72. 
This negative voltage serves to inhibit the operation of vertical 
oscillator 72 and thereby vertical scanning of kinescope 38. The displayed 
image consequently is vertically collapsed to a narrow horizontal line in 
the center of the display screen of the kinescope. 
In addition, in the "service" position, pole 84a is decoupled from ground 
potential, and the voltage appearing at the junction of resistors 92 and 
93 increases. The direct voltage then developed across color control 
potentiometer 90 and therefore the voltage appearing at the wiper of 
potentiometer 90 increases to a level greater than +11.2 volts due to the 
voltage divider action of the +11.2 volt and +22 volt sources, resistors 
92 and 93, and the resistance of potentiometer 90. This increased, 
positive direct voltage is in a direction to reduce the gain of (i.e., 
bias off) chrominance processing unit 16 so that substantially no 
chrominance signals are coupled through chrominance processing unit 16, 
and chrominance signals are removed from the chrominance channel. 
A positive direct voltage also appears across brightness control resistor 
112 as a result of the voltage divider action of resistor 112, resistor 92 
and the +22 volt source. An increased positive voltage then appearing at 
the wiper of variable resistor 112 serves to raise the base voltage of 
clamp transistor 110 to a more positive level, corresponding to a 
"blacker-than-black" blanking reference level. A corresponding increased 
positive voltage consequently appearing at the junction of capacitor 104 
and the emitter of transistor 110 during the clamping conduction intervals 
serves to reverse bias luminance amplifier transistor 105. Luminance 
signals are insufficient to forward-bias transistor 105 into conduction 
during this time, and substantially no current flows in the emitter of 
transistor 105. 
Since the luminance and chrominance channels are rendered inoperative to 
couple luminance and chrominance signal components to kinescope 38 in the 
"service" mode, the amplifier transistors (e.g., 24c) of the kinescope 
driver stages are caused to provide quiescent direct voltages to 
respective cathodes of kinescope 38 approximately equal to that provided 
by a lack of luminance and chrominance signals. In this condition, color 
temperature adjustments of kinescope 38 can be accomplished by adjusting 
the fixed voltages applied to kinescope 38 from screen control unit 42 
such that the separate guns are on the threshold between conduction and 
cut-off. 
It is further noted that in the "service" position poles 86a and 88a are 
connected together through a negligible impedance so that pole 88a is at 
ground potential. The ground potential appearing at pole 88a and coupled 
to the control input of auxiliary blanking unit 145 serves to inhibit the 
operation of unit 145, thereby decoupling the auxiliary blanking pulse 
from the kinescope driver stages. The auxiliary blanking pulse would 
otherwise upset the quiescent operating condition of the kinescope drivers 
and therefore upset the color temperature adjustment of kinescope 38. The 
connection from pole 88a to auxiliary blanking unit 145 is not necessary 
in the absence of the auxiliary blanking pulse. The latter connection is 
the only AC signal coupling connection to switch 82, the remainder of the 
connections coupling DC signals. Noise pick-up, interference signals, and 
other problems such as capacitive loading, often associated with long 
connections coupling AC signals to a service switch, therefore are 
significantly reduced by the arrangement of FIGS. 1a and 1b. 
Since video processing unit 12 is not disabled in the "service" mode, unit 
12 continues to provide a composite video signal including luminance, 
chrominance and synchronization (sync) components. At this time, the 
chrominance and luminance components normally coupled via the chrominance 
and luminance channels are inhibited from reaching kinescope 38 as 
discussed. Also, horizontal oscillator 62 operates at a substantially 
constant desired horizontal line frequency (e.g., 15,734 Hz) in response 
to the frequency sychronizing sync component provided by sync separator 
30, since this component is coupled to oscillator 62 independent of the 
position of switch 82. 
The frequency of the oscillatory output signal of horizontal oscillator 62 
is susceptible to slight variations (e.g., due to temperature changes or 
spurious signals such as noise) in the absence of the sync component 
(e.g., if the video IF stage of video processor 12 were disabled). 
Unregulated receiver operating voltages derived from horizontal flyback 
transformer 76 in response to the horizontal output signal coupled to 
transformer 76 would then undesirably vary in magnitude. Such receiver 
operating voltages can include the +210 volt operating voltage as shown, 
as well as an operating voltage associated with the screen grids of 
kinescope 38, for example. 
The +210 volt operating voltage for kinescope driver stages 18a, 18b and 
18c can, for example, be derived via a rectifier 79 and a filter capacitor 
80 from a transformer secondary winding voltage waveform comprising 
periodic positive flyback pulses (e.g., 210 volts peak amplitude) 
coincident with horizontal retrace intervals. 
In the absence of the sync component, variations of the frequency of the 
horizontal oscillator output signal cause corresponding variations in the 
timing of the positive pulse voltage waveform derived from the secondary 
winding of transformer 76. An increase or decrease of the horizontal 
oscillator signal frequency produces a corresponding decrease or increase 
in the duration of the signal trace interval relative to the retrace 
interval (the retrace interval remains substantially constant in this 
example). A corresponding increase or decrease in the positive 210 volt 
operating voltage therefore results, since the magnitude of the rectified 
and filtered average direct voltage provided by diode 79 and capacitor 80 
is a function of the positive duty cycle of each retrace-trace period. 
As a more specific example, when the frequency of the horizontal oscillator 
output signal decreases, the trace interval of the positive pulse voltage 
waveform increases relative to the retrace interval, so that the positive 
duty cycle and therefore the average positive DC level of the positive 
pulse voltage waveform decreases. A rectified positive DC voltage somewhat 
less than the desired 210 volts therefore results. A frequency variation 
of .+-.500 Hz can cause the desired +210 volt supply to vary 10-15 volts. 
In essence, a desired level of unregulated operating voltages derived in 
this manner depends upon operation of horizontal oscillator 62 at the 
proper frequency. In this example, if horizontal oscillator 62 were not 
synchronized by the sync component during the service mode, the kinescope 
driver operating supply voltage (+210 volts) would change if the frequency 
of oscillation changed. Kinescope set-up adjustments performed under such 
condition would be inaccurate, since the kinescope driver operating supply 
voltage would revert to normal in the "normal" mode, when the operating 
frequency of oscillator 62 is properly established (synchronized) in 
response to the sync component. 
Thus normal quiescent operating conditions of the receiver are closely 
simulated, and accurate kinescope set-up adjustments are facilitated, by 
maintaining horizontal oscillator 62 responsive to the sync component 
during the "service" mode in a system of the type described above. 
Referring now to FIG. 2, there is shown a less complex, more economical 
service switch 282 including "normal" and "service" positions. 
Switch 282 includes three poles 283, 285 and 287. Pole 283 is connected to 
the control input of vertical oscillator 72 (FIG. 1b), and pole 285 is 
connected to a source of negative direct voltage (-40 volts). Pole 287 is 
connected to the junction of resistors 92 and 93 (FIG. 1b) and also to a 
point in a voltage divider network including series coupled resistors 295, 
296 and 297 connected between a source of positive direct voltage (+210 
volts) and a source of negative direct voltage (-40 volts). The junction 
of resistors 296 and 297 is coupled to the control grids of kinescope 38. 
In the "normal" position, the receiver and the brightness and color control 
circuits operate normally as mentioned previously. It is noted, however, 
that in the arrangement of FIG. 2 the brightness and color control 
circuits are biased with respect to the -40 volt source via poles 285 and 
287 which are connected to the junction of resistors 92 and 93 in FIG. 1b. 
In comparison, it is noted that in the arrangement of FIG. 1b with service 
switch 82, the junction of resistors 92, 93 is coupled to ground potential 
in the "normal" position of service switch 82 via poles 84a and 86a. 
Accordingly, with the arrangement of FIG. 2, the values of resistors 92 
and 93 should be selected so that brightness control 112 and color control 
90 provide a desired amount of control in the normal operating mode. 
Also in the normal mode, a first voltage appears at the junction of 
resistors 296 and 297 for biasing the control electrodes of kinescope 38. 
When service switch 282 is in the "service" position, the negative direct 
voltage source (-40 volts) is coupled from pole 285 via a negligible 
impedance and pole 283 to the control input of vertical oscillator 72 
(FIG. 1b) to collapse the vertical scan as discussed previously. A 
kinescope control electrode bias voltage of increased magnitude then 
appears at the junction of resistors 296 and 297. This control grid bias 
voltage is in a direction to cause kinescope 38 to product (i.e., turn on) 
or to approach conduction. The kinescope is then adjusted by adjusting the 
voltages coupled to kinescope 38 by screen control unit 42 so that the 
separate guns are at a threshold level between conduction and cut-off. The 
bias voltage of the control grids is returned to the first bias voltage 
when service switch 282 is returned to the "normal" position. 
Although the invention has been described in terms of specific embodiments, 
it should be recognized that other arrangements may be devised by those 
skilled in the art without departing from the scope of the invention.