CDE MOD. 8017-31 CHASSIS PE20 INTERNAL VIEW.

The chassis is a monocarrier ICs based:

TDA3190

TBA950


TDA3190 TV SOUND CHANNEL (sgs)

The TDA3190 is a monolithic integrated circuit in a
16-lead dual in-line plastic package. It performs all
the functions needed for the TV sound channel :

.IF LIMITER AMPLIFIER .ACTIVE LOW-PASS FILTER
.FM DETECTOR
.DC VOLUMECONTROL
.AF PREAMPLIFIER .AF OUTPUT STAGE

DESCRIPTION
The TDA3190 can give an output power of 4.2 W
(d = 10 %) into a 16 W load at VS = 24 V, or 1.5 W
(d = 10 %) into an 8 W load at VS = 12 V. This
performance, togetherwith the FM-IF section characteristics
of high sensitivity, highAM rejection and
low distortion, enables the device to be used in
almost every type of television receivers.
The device has no irradiation problems, hence no
external screening is needed.
The TDA3190 is a pin to pin replacement of
TDA1190Z.

The electrical characteristics of the TDA3190 remain
almost constant over the frequencyrange 4.5
to 6 MHz, therefore it can be used in all television
standards (FM mod.). The TDA3190 has a high
input impedance,so it can work with a ceramic filter
or with a tuned circuit that provide the necessary
input selectivity.
The value of the resistors connected to pin 9,
determine the AC gain of the audio frequency amplifier.
This enables the desired gain to be selected
in relation to the frequency deviation at which the
output stage of the AF amplifier, must enter into
clipping.
Capacitor C8, connected between pins 10 and 11,
determines the upper cutoff frequency of the audio
bandwidth.To increase the bandwidth
the values of C8 and C7 must be reduced, keeping the ratio
C7/C8 as shown in the table of fig. 16.
The capacitor connected between pin 16 and
ground, together with the internal resistor of 10 KW
forms the de-emphasis network. The Boucherot
cell eliminates the high frequency oscillations
caused by the inductiveload and thewires connecting
the loudspeaker.


TBA950 line oscillator combination
DESCRIPTION
The line oscillator combination TBA920/950 is a monolithic
integrated circuit intended for the horizontal deflection of the black and white
and colour TV sets
picture tube.

FEATURES:
SYNC-PULSE SEPARATION
OPTIONAL NOISE INVERSION
GENERATION OF A LINE FREQUENCY VOL-
TAGE BY MEANS OF AN OSCILLATOR
PHASE COMPARISON BETWEEN SYNC-
PULSE AND THE OSCILLATOR WAVEFORM
PHASE COMPARISON BETWEEN THE OS-
CILLATOR WAVEFORM AND THE MIDDLE OF
THE LINE FLY-BACK PULSE
AUTOMATIC SWITCHING OF THE VARIABLE
TRANSCONDUCTANCE AND THE VARIABLE
TIME CONSTANT TO ACHIEVE NOISE SUP-
PRESSION AND, BY SWITCHING OFF, POS-
SIBILITY OF TAPE-VIDEO-REGISTERED RE-
PRODUCTION
SHAPING AND AMPLIFICATION OF THE OS-
CILLATOR WAVEFORM TO OBTAIN PULSES
FOR THE CONTROL OF DRIVING STAGES IN
HORIZONTAL, DEFLECTION CIRCUITS
USING EITHER TRANSISTORS OR THYRISTORS.



Power Supply: The examples chosen are taken from manufacturers' circuit diagrams and are usually simplified to emphasise the fundamental nature of the circuit. For each example the particular transistor properties that are exploited to achieve the desired performance are made clear. As a rough and ready classification the circuits are arranged in order of frequency: this part is devoted to circuits used at zero frequency, field frequency and audio frequencies. Series Regulator Circuit Portable television receivers are designed to operate from batteries (usually 12V car batteries) and from the a.c. mains. The receiver usually has an 11V supply line, and circuitry is required to ensure that the supply line is at this voltage whether the power source is a battery or the mains. The supply line also needs to have good regulation, i.e. a low output resistance, to ensure that the voltage remains constant in spite of variations in the mean current taken by some of the stages in the receiver. Fig. 1 shows a typical circuit of the power -supply arrangements. The mains transformer and bridge rectifier are designed to deliver about 16V. The battery can be assumed to give just over 12V. Both feed the regulator circuit Trl, Tr2, Tr3, which gives an 11V output and can be regarded as a three -stage direct -coupled amplifier. The first stage Tr 1 is required to give an output current proportional to the difference between two voltages, one being a constant voltage derived from the voltage reference diode D I (which is biased via R3 from the stabilised supply). The second voltage is obtained from a preset potential divider connected across the output of the unit, and is therefore a sample of the output voltage. In effect therefore Tr 1 compares the output voltage of the unit with a fixed voltage and gives an output current proportional to the difference between them. Clearly a field-effect transistor could do this, but the low input resistance of a bipolar transistor is no disadvantage and it can give a current output many times that of a field-effect transistor and is generally preferred therefore. The output current of the first stage is amplified by the two subsequent stages and then becomes the output current of the unit. Clearly therefore Tr2 and Tr3 should be current amplifiers and they normally take the form of emitter followers or common emitter stages (which have the same current gain). By adjusting the preset control we can alter the fraction of the output voltage' applied to the first stage and can thus set the output voltage of the unit at any desired value within a certain range. By making assumptions about the current gain of the transistors we can calculate the degree of regulation obtainable. For example, suppose the gain of Tr2 and Tr3 in cascade is 1,000, and that the current output demanded from the unit changes by 0.1A (for example due to the disconnection of part of the load). The corresponding change in Tr l's collector current is 0.1mA and, if the standing collector current of Tr 1 is 1mA, then its mutual conductance is approximately 4OmA/V and the base voltage must change by 2.5mV to bring about the required change in collector current. If the preset potential divider feeds one half of the output voltage to Tr l's base, then the change in output voltage must be 5mV. Thus an 0.1A change in output current brings about only 5mV change in output voltage: this represents an output resistance of only 0.0552.



 THE TBA920 SYNC/TIMEBASE IC It has been quite common for some time for sync separation to be carried out in an i.c. but until 1971 this was as far as i.c.s had gone in television receiver timebase circuitry. With the recent introduction of the delta featured 110°  colour series however i.c.s have gone a step farther since this chassis uses a TBA920 as sync separator and line generator. A block diagram of this PHILIPS /Mullard  i.c. is shown in Fig. 1.
The video signal at about 2-7V peak -peak is fed to the sync separator section at pin 8, the composite sync waveform appearing at pin 7.
The noise gate switches off the sync separator when a positive -going input pulse is fed in at pin 9, an external noise limiter circuit being required .
The line sync pulses are shaped by R1 /C1 /C2/R2 and fed in to the oscillator phase detector section at pin 6.
The line oscillator waveform is fed internally to the oscillator phase detector circuit which produces at pin 12 a d.c. potential which is used to lock the line oscillator to the sync pulse frequency, the control potential being fed in at pin 15. The oscillator itself is a CR type whose waveform is produced by the charge and discharge of the external capacitor (C7) connected to pin 14. The oscillator frequency is set basically by C7 and R6 and can be varied by the control potential appearing at pin 15 from pin 12 and the external line hold control. Internally the line oscillator feeds a triangular waveform to the oscillator and flyback phase detector sections and the pulse width control section. The coincidence detector section is used to set the time constant of the oscillator phase detector circuit. It is fed internally with sync pulses from the sync separator section, and with line flyback pulses via pin 5. When the flyback pulses are out of phase with the sync pulses the impedance looking into pin 11 is high (21(Q). When the pulses are coincident the impedance falls to about 150Q and the oscillator phase detector circuit is then slow acting. The effect of this is to give fast pull -in when the pulses are out of sync and good noise immunity when they are in sync. The coincidence detector is controlled by the voltage on pin 10. When the sync and flyback pulses are in sync C3 is charged: when they are out of sync C3 discharges via R3. VTR use has been taken into consideration here. With a video recorder it is necessary to be able to follow the sync pulse phase variations that occur as a result of wow and flutter in the tape transport system, while noise is much less of a problem. For use with a VTR therefore the network on pin 10 can simply be left out so that the oscillator phase detector circuit is always fast acting. A second control loop is used to adjust the timing of the pulse output obtained from pin 2 to take into account the delay in the line output stage. The fly back phase detector compares the frequency of the flyback pulses fed in at pin 5 with the oscillator signal which has already been synchronised to the sync pulse frequency.
Any phase difference results in an output from pin 4 which is integrated and fed into the pulse width control section at pin 3. The potential at pin 3 sets the width of the output pulse obtained at pin 2: with a high positive voltage (via R11 and R12) at pin 3 a 1:1 mark -space ratio out- put pulse (32/us on, 32/us off) will be produced while a low potential at pin 3 (negative output at pin 4) will give a 16us output pulse at  the same frequency. The action of this control loop continues until the fly- back pulses are in phase with a fixed point on the oscillator waveform: the flyback pulses are then in phase with the sync pulses and delays in the line output stage are compensated. The output obtained at pin 2 is of low impedance and is suitable for driving valves, transistors or thyristors: R9 is necessary to provide current limiting.

INTEGRATED circuits are slowly but surely taking over more and more of the circuitry used in television sets even B/W.
The first step, some many years ago now, was to wrap the 6MHz intercarrier sound strip into a neat package such as the TAA350 or TAA570. Then came the "jungle" i.c. which took over the sync separator and a.g.c. operations. Colour receiver decoder circuitry was the next obvious area to be parcelled up in i.c. form,  two i.c. decoder and the more sophisticated Philips four i.c. design was coming on the scene. The latter is about to be superseded by a three i.c. version in which the TBA530 and TBA990 are replaced by the new TCA800 which provides chrominance signal demodulation, matrixing, clamping and preamplification, with RGB outputs of typically 5V peak -to -peak.
To improve performance a number of sets adopted a synchronous detector i.c.-the MC1330P -for vision demodulation, which of course overcomes the problem of quadrature distortion. In one monochrome chassis this i.c. is partnered by a complete vision i.f. strip i.c., the MC1352P. In the timebase section the TBA920 sync separator/line generator i.c. has found its way into several chassis was a Texas's SN76544N 07 i.c. which wraps up the sync separator and both the field and line timebase generators has come into use. Several monochrome portables have had in use a high -power audio output i.c. as the field output stage. Audio i.c.s are of course common, and in several  chassis the Philips TCA270 has put in an appearance. This device incorporates a synchronous detector for vision demodulation, a video preamplifier with noise inversion and the a.g.c. and a.f.c. circuits. The   development to be adopted in a production chassis was that remarkable Plessey i.c., the SL437F, which combines the vision i.f. strip, vision demodulator, a.g.c. system and the intercarrier sound channel.

SGS-Aces Range
Now, from the, at the time,  Italian Development Division of SGS-Ates, comes a new range of i.c.s which SGS  will set a standard pattern for TV chassis IN 1975. How this range combines to provide a complete colour receiver is shown in Fig. 1. The only sections of the receiver left in discrete component form are the video output stages, the tuner, the a.f.c. circuit and of course the line output stage and power supplies. It will be seen that the colour decoder section is split up as in the Philips three i.c. design. The TDA1150 chrominance and burst channel carries out the same functions as the TBA560, the TDA1140 reference section the same functions as the TBA540 and the TDA1160 chrominance demodulator/matrix- ing i.c. the same functions as Philips's new TCA800. It looks therefore as if this basic decoder pattern could become widely established. The other five i.c.s in the range are common to both colour and monochrome receivers. Particularly interesting are the TDA1170 which comprises a complete monochrome receiver field timebase-for colour set use an output stage using discrete com- ponents is suggested-and the TDA440 which incorporates the vision i.f. strip, vision detector and a.g.c. circuitry. The intercarrier sound i.f. strip is neatly packed away with the audio circuitry in the TDA1190 while the TDA1180 sync separator/line oscillator i.c. is a very similar animal to the now well known TBA920. The fifth i.c., the TBA271, is a stabiliser for the varicap tuner tuning supply. The novel i.c.s in this family then were the TDA 440, TDA1170 and the TDA1190 and we shall next take a closer look at each of these.

Vision IF IC:
The TDA440 vision i.f. strip i.c. is housed in a 16 -pin plastic pack with a copper frame. There is a three -stage vision i.f. amplifier with a.g.c. applied over two stages, synchronous vision demodulator, gated a.g.c. system and a pair of video signal pre amplifiers which provide either positive- or negative - going outputs. Fig. 2 shows the i.c. in block diagram form. It is possible to design a very compact i.f. strip using this device and very exact performance is claimed. Note that apart from the tuned circuits which shape the passband at the input the only tuned circuit is the 39.5MHz carrier tank circuit in the limiter/demodulator section. The only other adjustments are the tuner a.g.c. delay potentiometer and a potentiometer (the one shown on the right-hand side) which sets the white level at the demodulator. This of course gives ease of setting up, a help to setmaker and service department alike. For a sensitivity of 200/4V the output is 3.3V peak - to -peak, giving an overall gain in the region of 82 to 85dB. The a.g.c. range is 55dB, a further 30 to 40dB being provided at the tuner. The tuner a.g.c. output is intended for use with a pnp transistor or pin diode tuner unit: an external inverter stage is required with the npn transistor tuner units generally used. discrete component video output stage; in a colour In a monochrome set the output would be fed to a design the output is fed to the chrominance section of the TDA1150 and, via the luminance delay line, to the luminance channel in the TDA1150. Also of course in both cases to the sync separator which in this series of i.c.s is contained in the TDA1180.

Field Timebase IC :
The TDA1170 field timebase i.c. is shown in block diagram form in Fig. 3. The i.c. is housed in a 12 -pin package with copper frame and heat dissipation tabs. It is capable of supplying up to 1.6A peak -to -peak to drive any type of saddle -wound scanning yoke but for a colour receiver it is suggested that the toroidal deflection coil system developed by RCA is used. In this case the i.c. acts as a driver in conjunction with a complementary pair of output transistors. The yoke current in this case is in the region of 6A. The TDA1170 is designed for operation with a nominal 22V supply. It can be operated at up to 35V however. A voltage doubler within the i.c. is brought into action during the flyback time to raise the supply to 70V. Good frequency stability is claimed and the yoke current stability with changes in ambient temperature is such that the usual thermistor in series with the field coils is not required. For monochrome receiver use the power supplied to the yoke would be 0-83W for a yoke current of lA peak -to -peak with a 1012 coil impedance and 20V supply. As the power dissipation rating of the i.c. is 2.2W no further heatsink is required. For use in a colour receiver with a toroidal coil impedance of 1.6Ohm the scanning current would be 7A peak -to -peak. The power supplied to the yoke may be as much as 6.5W while the dissipation in the i.c. would be up to 2-3W. In this case a simple heatsink can be formed from a thin copper sheet soldered to the heat fins- an area of about 3-4 sq. in. should be adequate. The sync circuit at the input gives good noise immunity while the difference between the actual and ideal interlace is less than 0-3% of the field amplitude. Because of the high output impedance a relatively low value (1/iF or less) output coupling capacitor can be used. This means that mylar types instead of electrolytics can be used, reducing the problems of linearity and amplitude stability with respect to temperature and ageing. The external controls shown in Fig. 3 are hold, height and linearity (from left to right).

Complete Sound Channel:
The TDA1190 sound channel (see Fig. 4) is housed in a 12 -pin package. Possible radiation pick-up and thermal feedback risks have been avoided by careful layout of the chip. This pack also has a copper frame, with two cooling tabs which are used as the earthing terminals. The built-in low-pass filter overcomes radiation problems and with a response 3dB down at 3MHz allows for a flat amplitude response throughout the audio range: this particular feature will appeal to hi-fi enthusiasts as well since it makes the i.c. a good proposition for f.m. radio reception. The d.c. volume control has a range of 100dB. The external CR circuit (top, Fig. 4) sets the closed - loop gain of the power amplifier. The external feedback capacitor network (right) provides a.f. bandwidth and frequency compensation while the CR circuit across the output limits any r.f. which could cause severe audio distortion. The TDA1190 does not require an extra heatsink when operating in normal ambient temperatures-up to 55°C-because of the new technique of soldering the chip directly on to the copper frame that forms part of the external tabs. By doing this, SGS-Ates have reduced the thermal resistance of the device to 12°C per watt. The device can dissipate up to 2.2W at 55°C without using an external heatsink other than the printed circuit pad (about 2 sq. in.) which is soldered to the tab. The output stages of the TDA1190 are in quasi - complementary mode (with patented features), eliminating the need for bootstrap operation without loss of power. The absolute maximum output power is 4.2W with a supply voltage of 24V and a nominal loudspeaker impedance of 1612. At 12V and 812 an output of 1.8W can be achieved. Total harmonic distortion is 0.5% for 1 mV f.m. input and 2W output into 1611 at 24V. Satisfactory operation is possible over a voltage supply range of 9 to 28V, making this versatile i.c. suitable for a wide range of applications. The whole audio circuit can be mounted on a p.c.b. 2in. x 25in. without a heatsink.

Mounting: The complete family of i.c.s has been designed so that it can be incorporated in very small and simple printed circuit modules. The use of a copper frame assists in improving the thermal stability as well as facilitating the mounting of the i.c.s on the board. Where an extra heatsink is required this can be a simple fin added to the mounting tabs or a metal clamp on the top of the pack. SGS claim that insta- bility experienced with conventional layouts in colour receivers has been eliminated provided their recommendations are observed.

Power Supplies:
A simple power supply circuit without sophisticated stabilisation can be used. The requirements are for outputs ranging between 10V and 35V with adequate decoupling and smoothing. It was  possible to provide only three supply lines to feed the whole receiver system-plus of course the high- voltage supplies required by the c.r.t. The power supply requirements are simplified since the TDA1170 incorporates a voltage regulator for its oscillator, the TDA440 incorporates a regulator for the vision i.f. strip and the TDA1190 a regulator for the low -voltage stages and the d.c. volume control.