The ZANUSSI CHASSIS BS400 represents the spin off with the previous technology chassis based on THYRISTOR DEFLECTION SYSTEM and with all 20AX AND P.I.L. old generations TUBES technology.
First ZANUSSI chassis using the PHILIPS 30AX SYSTEM CRT TUBE FAMILY.
This chassis is entirely transistorized and has a power supply unit realized with SMPS technology.
The chassis BS400 is even more modular than the previous types but this trend will in the 80's quite abandoned with monocarrier chassis types.
It supports the p.c.boards and
it supplies voltages for EHT,
focusing system and CRT heaters.
CHASSIS : BS 400.2
PICTURE TUBE : 22" PIL s 4 - A 56-701 X OR A66/56-540X 30AX SYSTEM
POWER SUPPLY .. 240V AC + 10% 50 Hz
POWER ABSORBED : Medium/maximum 110/140 W
EHT : 24.5 kV
MAX. BEAM CURRENT . 1.1 InA
ANTENNA INPUT : 75 Ohm
TUNER .. Varicap integrated type
TUNING SYSTEM . Electronic (voltage synthesis type)
PRESELECTION . 16 TV programmes and VCR on programme 16
AFC : Insertable through pushbutton
REMOTE CONTROL . IR type. Max. range approx. 8 m
REMOTE CONTROL TRANSMITTER In stand-by < 20 /uA
CLOCK : Electronic programmable type with digital hours and minutes indication
AUXILIARY OUTPUT JACKS : Headphones jack 8 Ohm DIN 45327
Tape recorder 47 kOhm DIN 41524
External loudspeaker jack 2.7 Ohm
DIN 41529
LOUDSPEAKER : Lateral woofer and frontal tweeter
AUDIO OUTPUT . 15 W
STANDARD . CCIR - I PAL
DEGAUSSING : Automatic
DIMENSIONS : 55x55~42 cm
WEIGHT .. 29 kg
BS 400.2 Chassis
BS 417 Power supply p.c.b,
BS 395 Line output p.c.b.
BS 396 Synchro. separator and pincushion correction p.c.b.
BS 418 CRT discharger p.c.b.
BS 399 Video p.c.b.
BS 398 IF unit p.c.b.
BS 397 Vertical deflection p.c.b. A
Pl AGC adjustment potentiometer
P 351 Vertical linearity adjustment potentiometer .
P 352 Vertical frequency adjustment potentiometer
P 353 Vertical amplitude adjustment potentiometer
P 354 Raster adjustment potentiometer
P 551 Potentiometer for (grid-2) adjustment of picture tube
BS 418 CRT discharger p.c.b.
SW 553 Switch for blue electron gun
SW 552 Switch for green electron gun
P 552 Focus adjustment potentiometer
SW 551 Switch for red electron gun
BS 417 Power supply p.c.b.
P 303 Potentiometer for adjustment of +12.6v DC
P 301 Potentiometer for adjustment of +15OV DC
P 401 Oscillator frequency adjustment potentiometer
P 402 Pincushion adjustment potentiometer
P 403 Horizontal amplitude adjustment potentiometer
BS 395 Line output p.c.b.
BS 396 Synchro. separator and pincushion correction p.c.b.
BS 397 Vertical deflection p.c.b.
BS 398 IF unit p.c.b.
BS 399 Video p.c.b.
P 108 Peak-to-peak adjustment potentiometer (blue)
P 109 Black level adjustment potentiometer (blue)
P 106 Peak-to-peak adjustment potentiometer (green)
P 107 Black level adjustment potentiometer (green)
P 104 Peak-to-peak adjustment potentiometer (red)
P 105 Black level adjustment potentiometer (red)
P 103 Potentiometer for adjustment of direct signal level
L 102 Burst phase adjustment coil
C 123 Capacitive trimmer for oscilloscope adjustment
Transistors mounted on chassis and p.c.boards
Transistors Type Electronic functions
Tl BF 479 S UHF amplifier
T3 BF 680 Oscillator/convertor UHF
T4 BF 506 UHF amplifier
T6 BF 199 IF amplifier
T7 BC 548 B Audio amplifier
T8 BC 548 B Impedance matcher
T 101 BC 548 B Automatic control of p.p. luminance signal
T 1 0 2 BC 548 B Brightness control fixed level setting for adjustment of the output viideo amplifiers
T 103 BC 548 B T 101 driver
T 104 BC 548 B Suppressor of unwanted reflections on
the burst signal delay line LR 102 of
the chrominance channel
T 105 BF 393 Active load
T 106 BF 758 Video output
T 107 BF 393 Active load
T 108 BF 758 Video output
T 109 BF 393 Active load
T 110 BF 758 Video output
T 261 TIL 78 Optoelectric coupler
T 262 BC 548 B Amplifier
T 263 BC 548 Switching transistor
T 264 BC 320 B Switching transistor
T 265 BC 548 B Driver for optoelectric coupler
T 266 BC 320 B Driver for optoelectric coupler
T 301 BC 557 B Amplifier
T 302 BU 326 A Oscillator
T 303 BC 548 B Switch for remote control
T 351 BD 135 Switching transistor
T 352 BD 243 A Vertical parabola amplifier
T 353 BD 244 A Vertical parabola amplifier
T 354 BC 548 B Multivibrator for formation of vertical
T 355 BC 548 B blanking pulse
T 402 BC 548 C Parabola signal amplifier
T 403 BC 558 B Parabola signal amplifier
T 404 BD 679 Amplifier
T 451 BF 758 Amplifier switch
T 452 BU 208 A Line output
Transistors mounted on remote control and tuning unit
Transistors Type Electronic functions
T 702 BC 547 B Driver for DL 651
T 704 BC 547 B AFC enabler
T 705 BC 547 B Clipper
T 801 BC 413 C AGC
T 802 BC 413 C Amplifier
T 803 BC 413 C Amplifier
T 804 BC 253 C Amplifier
T 805 BC 170 C Square-wave shaping
T 806 BC 320 B Driver for display's lit spot
T 807 BC 320 B Driver for display's lit spot
T 808 BC 320 B Driver for display's lit spot
T 809 BC 548 B Colour adjustment
T 8i0 BC 548 B Volume adjustment
T 811 BC 320 B Muting
T 812 BC 548 B Muting
T 813 BC 548 Output impedance matcher
T 814 BC 548 Output impedance matcher
T 815 BC 548 Output impedance matcher
MAIN COMPONENTS
BS 400.2 Chassis - It supports the p.c.boards and it supplies voltages for EHT, focusing system and CRT heaters.
BS 398 Tuner - IF video/audio - Conversion of the RF signal into p.c.b. an IF signal (video carrier: 39.5 MHz;, audio carrier: 33.5 MHZ). Detection of the IF signal into low frequency video and audio signals.
BS 399 Luminance-chrominance and - This p.c.b. processes the video amplifier p.c.b. complete composite video signal coming from the IF p.c.b. and supplies the R-G-B signals to the picture tube.
BS 401 Audio p.c.b. - This p.c.b. receives the audio signal (not adjusted in volume) coming from p.c.b. BS 398, it adjusts it in amplitude and tone, it amplifies it and sends it to drive the two receiver's loudspeakers (tweeter and woofer). Through jack PR 201 it is possible to connect externally an auxiliary 2.7 Ohm loudspeaker with or without the exclusion of the internal loudspeakers. Furthermore, the p.c.b. transferes the audio signal (not adjusted in volume) to taperecorder and headphone jacks. No adjustments needed.
BS 470 Mains filter p.c.b. - The p.c.b. includes circuits relevant to: mains filter, degaussing, remote control SUPPlY, start remote control. No adjustments needed.
BS 380 Power supply p.c.b. - It includes circuits for clock supply and for switch-ON programming. . No adjustments needed.
BS 417 Power supply p.c.b. - It converts the mains voltage in DC voltage available at five outputs with values of: +2OOV; +15OV; +27V (two outputs); +12.6v. These voltages are stabilized and separated from the mains.
BS 397 Vertical deflection p.c.b. - This p.c.b. generates a sawtooth voltage at frame frequency which is used for driving the vertical deflection yoke. It supplies a similar voltage to the l'pincushionll section of the synchro. separator p.c.b. to obtain the E/W pincushion correction. It supplies a frame frequency pulse which is used for the luminance, chrominance and video amplifier p.c.b. blankings. It receives the vertical synchro. from the synchro. separator p.c.b. and receives from the chassis a voltage proportional to the beam current.
BS 396 Synchro. separator and - The p.c.b. processes the video pincushion correction signal. Said process consists in p.c.b. separating the horizontal signals from the video composite signal. The "pincushion correctionl' section receives a sawtooth shaped signal and converts it into a parabolic shape for E/W correction.
BS 395 Horizontal deflection - This p.c.b. amplifies the pulse p.c.b. sequence at line frequency and drives a circuit operating as an ON-OFF switch for supplying the deflection current to the horizontal yoke. It also receives the parabolic signal which acts on the diodes modulator for E/W correction. No adjustments needed.
BS 418 CRT p.c.b. It includes protection and matching circuits for the three signals (red, green and blue) with relevant voltage dischargers. In series to each signal circuit a switch is provided for black level adjustment. The p.c.b. includes a cut-OFF circuit which stops the CRT luminous emission during the blanking phase.
BS 385 Auxiliary outputs jacks - This p.c.b. receives the audio p.c.b. signal (amplified and volume adjusted) and supplies it to an auxiliary jack for private headphone listening. A non-volume-regulated signal is also supplied to a socket for taperecording. The headphones output complies to Standard DIN-45327 and has an impedance of 8 Ohm. The taperecorder output complies to Standard DIN-41524 and has an impedance of 47 k0hm. No adjustments needed.
BS 387 IR preamplifier p.c.b. - It converts IR pulses coming from the transmitter into electrical pulses. These are amplified and appropriatly clipped. No adjustments needed.
BS 389 Remote control receiver - It receives the command signals p.c.b. coming from the sequential programme pushbutton, it processes them and converts them into control signals. Tone and contrast controls also pass through this p.c.b., said control signals being fed from the control unit and being forwarded to the chassis. No adjustments needed.
BS 405 Front control unit p.c.b. - This p.c.b. includes potentiometers for volume, brightness, saturation, contrast, treble and bass. This p.c.b. also includes pushbuttons relevant to sequential control, AFC, automatic search, forward tuning, bachward tuning, band and tuning indicating LEDs.
The display indicates the programme selected. Furthermore, this p.c.b. includes all pushbuttons for clock adjustment. No adjustments needed.
BS 388 Tuning unit p.c.b. - Automatic searching of a TV station through a start command. Manual searching of a TV station through two commands (increment and decrement). Inclusion-exclusion of the AFC circuit with LED display. Band indication displayed on three LEDs. Tuning level indication with five LEDs. Memorization of 16 selected programmes manually or with remote control. No adjustments needed.
BS 414 a/b Remote control p.c.b. - This p.c.b. enables remote control of the following functions: selection of 16 programmes; "+" or "-" volume adjustment; brightness and saturation adjustment; audio silencing; TV receiver ON/OFF switching. No adjustments needed.
Although the main chassis is insulated from mains, part of the power supply chassis bears mains voltage. This therefore should not be connected to earth during servicing. Do not install, remove, or handle the picture tube in any manner unless shatter-proof goggles are worn. People not so equipped should be kept away while picture tubes are handled. Keep picture-tube away fron the body while handling. Before returning a serviced receiver to the customer, the service technician must thoroughly test the unit to be certain that it is completely safe to operate without danger of electrical shock, and be sure that no protective device built into the instrument by the manufacturer has become defective, or inadvertently defected during servicing.
SELECO (ZANUSSI) 22ST303 "BIG" CHASSIS BS400 Simplified horizontal / line deflection circuit.
This SELECO (ZANUSSI) 22ST303 "BIG" CHASSIS BS400 Series was featuring a Simplified BU208A transitor horizontal deflection section replacing all Thyristor horizontal timebase based circuits.
A horizontal deflection circuit makes a sawtoothcurrent flow through a deflection coil. The current
will have equal amounts of positive and negative
current. The horizontal switch transistor conducts
for the right hand side of the picture. The damper
diode conducts for the left side of the picture.
Current only flows through the fly back capacitor
during retrace time.
For time 1 the transistor is turned on. Current
ramps up in the yoke. The beam is moved from the
center of the picture to the right edge. Energy is
stored on the inductance of the yoke.
E=I2L/2
For time 2 the transistor is turned off. Energy
transfers from the yoke to the flyback capacitor. At
the end of time two all the energy from the yoke is
placed on the flyback capacitor. There is zero
current in the yoke and a large voltage on the
capacitor. The beam is quickly moved from the
right edge back to the middle of the picture.
During time 3 the energy on the capacitor flowsback into the yoke. The voltage on the flyback
capacitor decreases while the current in the yoke
builds until there is no voltage on the capacitor. By
the end of time 3 the yoke current is at it's
maximum amount but in the negative direction.
The beam is quickly deflected form the center to the
left edge.
Time 4 represents the left hand half of the picture.
Yoke current is negative and ramping down. The
beam moves from the left to the center of the
picture.
The current that flows when the horizontal switch is
closed is approximately:
Ipk ≅ Vcc T / Ldy
Ipk = collector current
T = 1/2 trace time
Ldy = total inductance (yoke + lin coil + size coil)
note:The lin coil inductance varies with current.
______
Tr ≅ 3.14 √ L C
The current that flows during retrace is produced by
the C and L oscillation. The retrace time is 1/2 the
oscillation frequency of the L and C.
I2L /2 ≅ V2C /2 or I2L = V2C As stated earlier the energy in the yoke moves to the
flyback capacitor during time 2.
V= the amount of the flyback pulse that is above the
supply voltage.
D.C. annualizes is inductors are consideredshores, capacitors are open and generally
semiconductors are removed. The voltage at the
point “B+” is the supply voltage. The collector
voltage of Q1 is also at the supply voltage. The
voltage across C2 is equal to the supply voltage.
When we A.C. annualize this circuit we will find
that the collector of Q1 has a voltage that ranges
from slightly negative to 1000 volts positive. The
average voltage must remain the same as the D.C.
value.
In the A.C. annualizes of the circuit, the
inductance of the yoke (DY) and the inductance of
the flyback transformer are in parallel. The
inductance of T2 is much larger than that if the
DY. This results is a total system inductance of
about 10% to 20% less than that of the DY it’s
self.
The voltage across the Q1 is a half sinusoid pulse during the flyback or retrace period and close to zero at
all other times. It is not possible or safe to observe this point on an oscilloscope without a proper high
frequency high voltage probe. Normally use a 100:1 probe suitable for 2,000V peak. The probe must have
been high frequency calibrated recently.
HORIZONTAL SIZE / E/W AMPLITUDE - CORRECTION CIRCUIT:
There are several different methods of adjusting horizontal size.
SIZE COILAdd a variable coil to the yoke current path
causes the total inductance to vary with the coils
setting.
The yoke current is related to supply voltage,
trace time and total inductance. This method
has a limited range!
The horizontal section uses a PWM to set the
horizontal size. One DAC sets the horizontal
size and another DAC sets the pincushion and
trap.
The Raster Centering (D.C. centering) is
controlled by a DAC.
On small monitors the retrace time is fixed. On
large monitors or wide frequency range monitors
two different retrace times are available. The flyback time is set by the micro computer by selecting two
different flyback capacitors. At slow frequencies the longer retrace time is selected.
Different S corrector capacitor values are selected by the micro computer. At the highest frequency the
smallest capacitor is selected.
SPLIT DIODE MODULATORThis horizontal circuit consists of two parts. D1, C1, C2 and DY are the components as described above.
D2, C3, C4 and L1 are a second “dummy” horizontal section that does not cause deflection current. By the
D.C. analyzing this circuit the voltage across C2 + C4 must equal the supply voltage (B+). Deflection
current in the DY is related to the supply voltage minus the voltage across C4. For a maximum horizontal
size the control point must be held at ground. This causes the dummy section to not operate and the DY
section will get full supply voltage. If the control point is at 1/3 supply then the DY section will be
operating at 2/3 supply.
Note: The impedance of (D1,C1,C2 and DY) and (D2,C3,C4 and L1) makes a voltage divider. If thecontrol point is not connected then there is some natural voltage on C4. Most split diode monitors are built
to pull power from the dummy section through L2 to ground. A single power transistor shunts from the
control point to ground. It is true that power can be supplied from some other supply through L2 to rise the voltage on C4. For maximum range a bi-directional power amplifier can drive the control point.
The most exciting feature if the split diode modulator is that the flyback pulse, as seen by the flyback
transformer, is the same size at all horizontal size settings.
HORIZONTAL SWITCH/DAMPER DIODE
On the right hand side of the screen, the H. switch transistor conducts current through the deflection yoke.This current comes from the S correction capacitors, which have a charge equal to the effective supply
voltage. The damper diode allows current for the left hand side of the screen to flow back through the
deflection yoke to the S capacitors.
FLYBACK CAPACITOR
The flyback capacitor connects the hot side of the yoke to ground. This component determines the size and
length of the flyback pulse. ‘Tuning the flyback capacitor’ is done to match the timing of the flyback pulse
to the video blanking time of the video signal. The peak flyback voltage on the horizontal switch must be
set to less that 80% if the Vces specification. The two conditions of time and voltage can be set by three
variables (supply voltage, retrace capacitor and yoke inductance) .
S CAPACITOR
The S capacitors corrects outside versus center linearity in the horizontal scan. The voltage on the S cap
has a parabola plus the DC horizontal supply. Reducing the value of S cap increases this parabola thus
reducing the size of the outside characters and increasing the size of the center characters.
S Capacitor value: Too low: picture will be squashed towards edges.
Too high: picture will be stretched towards edges.
By simply putting a capacitor in series with each coil, the sawtooth waveform ismodified into a slightly sine-wave shape. This reduces the scanning speed near the
edges where the yoke is more sensitive. Generally the deflection angle of the electron
beam and the yoke current are closely related. The problem is the deflection angle
verses the distance of movement on the CRT screen does not have a linear effect.
BASE DRIVE CURRENT
The base drive resistor determines the amount of
base drive. If the transistor is over driven the Vsat
looks very good, but the current fall time is poor.
If the base current is too small the current fall time is very fast. The problem is that the transistor will have many volts across C-E when closed.
The best condition is found by placing the transistor in the heaviest load condition. Adjust the base resistor for the least power consumption then increase the base drive a small amount. This will slightly over drive the base.
BU208(A)
Silicon NPNnpn transistors,pnp transistors,transistors
Category: NPN Transistor, Transistor
MHz: <1 MHz
Amps: 5A
Volts: 1500V
HIGH VOLTAGE CAPABILITY
JEDEC TO-3 METAL CASE.
DESCRIPTION
The BU208A, BU508A and BU508AFI are
manufactured using Multiepitaxial Mesa
technology for cost-effective high performance
and use a Hollow Emitter structure to enhance
switching speeds.
APPLICATIONS:
* HORIZONTAL DEFLECTION FOR COLOUR TV With 110° or even 90° degree of deflection angle.
ABSOLUTE MAXIMUM RATINGS
Symbol Parameter Value Unit
VCES Collector-Emit ter Voltage (VBE = 0) 1500 V
VCEO Collector-Emit ter Voltage (IB = 0) 700 V
VEBO Emitter-Base Voltage (IC = 0) 10 V
IC Collector Current 8 A
ICM Collector Peak Current (tp < 5 ms) 15 A
TO - 3 TO - 218 ISOWATT218
Ptot Total Dissipation at Tc = 25 oC 150 125 50 W
Tstg Storage Temperature -65 to 175 -65 to 150 -65 to 150 oC
Tj Max. Operating Junction Temperature 175 150 150 °C
DESCRIPTIONS OF THE UNITS AND THEIR FUNCTIONS:
- BS394.2 POWER SUPPLY WITH BU326A It converts the mains voltage in DC voltage available at five outputs with values of: +2OOV; +15OV; +27V (two outputs); +12.6V. These voltages are stabilized and separated from the mains.SELECO (ZANUSSI) 22ST303 "BIG" CHASSIS BS400 Switching power supply, especially for a T.V. receiving apparatus:
SELECO (ZANUSSI) 22ST303 "BIG" CHASSIS BS400 Schaltnetzteil
(ZANUSSI BS394 SWITCH MODE POWER SUPPLY), IN GERMAN:
1. Schaltnetzteil,
insbesondere f·ur einen Fernsehempf·anger, mit einer Arbeitswicklung
(5), einem Schalttransistor (6), einer R·uckkopplungswicklung (7) und
einer Regelschaltung (ii) auf der Prim·arseite sowie mit Gleichrichtern
(15,16, 20) zur Erzeugung von Betriebsspannungen (U11U2#U3) auf der
Sekund·arseite eines Trenntransformators (1) gekenn zeichnet durch
folgende Merkmale: a) An eine Wicklung (19) ist ein Thyristor (24)
angeschlos sen, der f·ur die w·ahrend der siromf·uhrenden Phase der
Schalttransistoren (6) an der Wicklung (19) auftreten de Spannung in
Durchlassrichtung gepolt ist. b) An die Steuerelektrode des Thyristors
(24) ist eine der Betriebsspannungen (U2) in solcher H·ohe angelegt,
dass der Thyristor (24) im Normalbetrieb gesperrt bleibt und bei einem
unzul·assigen Anstieg der Betriebs spannung (U3) z·undet.
2. Netzteil nach Anspruch 1, dadurch gekennzeichnet, dass die Betriebsspannung (U3) ·uber einen Spannungsteiler (25,26) an die Steuerelektrode des Thyristors (24) angelegt ist.
3. Netzteil nach Anspruch 1, dadurch gekennzeichnet, dass die Wicklung (19) eine Sekund·arwicklung des Trenntransforma tors (1) ist.
Ein solches Schaltnetzteil enth·alt eine Regelschaltung zur Stabilisierung der Amplitude der auf der Sekund·arseite erzeugten Betriebsspannungen. In dieser Regelschaltung wird eine durch Gleichrichtung der Impulsspannung am Trafo gewonnene Stellgr·osse erzeugt und mit einer Bezugsspannung verglichen. In Abh·angigkeit von der Abweichung wird der Schaltzeitpunkt des auf der Prim·arseite vorgesehenen elektronischen Schalters so gesteuert, dass die Amplitude der erzeugten Betriebsspannungen konstant bleibt.
Bei einem solchen Schaltnetzteil kann die genannte Regelschaltung z.B. durch ein fehlerhaftes Bauteil ausfallen. Die Regelung der Amplitude der erzeugten Betriebsspannungen ist dann unkontrolliert. Die Betriebsspannungen k·onnen dann auf den doppelten oder dreifachen Wert ansteigen. Dadurch besteht die Gefahr, dass das Schaltnetzteil oder die an die Betriebsspannungen angeschlossenen Verbraucher wie z.B. der Heizfaden der Bildr·ohre oder der Zeilenendstufentransistor zerst·ort werden. Der Anstieg der Betriebsspannungen kann dar·uberhinaus einen Anstieg der im Fernsehempf·anger erzeugten Hochspannung und dadurch eine R·ontgenstrahlung ausl·osen.
Es ist auch ein Schaltnetzteil bekannt (DE-OS 27 27 332), bei dem zum Schutz gegen einen zu starken Anstieg der erzeugten Betriebsspannungen aus der Impulsspannung an der Prim·arseite des Trafos eine Stellgr·osse gewonnen wird, die beim ·Uberschreiten eines Schwellwertes den R·uckkopplungsweg unwirksam steuert. Durch die Unterbrechung des R·uckkopplungsweges kann das Schaltnetzteil nicht mehr schwingen, so dass in erw·unschter Weise auch keine Betriebsspannungen mehr erzeugt werden. Diese Schaltung erfordert jedoch eine Vielzahl von Bauteilen und ist daher relativ teuer.
Der Erfindung liegt die Aufgabe zugrunde, eine sicher wirkende Schutzschaltung mit verringertem Schaltungsaufwand gegen
die oben
beschriebenen Gefahren zu schaffen.Diese Aufgabe wird durch die im Anspruch 1 beschriebene Erfindung gel·ost. Vorteilhafte Weiterbildungen der Erfindung sind in den Unteranspr·uchen beschrieben.
Die Erfindung beruht auf folgender ·Uberlegung: Der Schalttransistor auf der Prim·arseite wird von der prim·arseitigen R·uckkopplungswicklung w·ahrend seiner stromleitenden Phase mit einem Basisstrom angesteuert. Wenn jetzt eine Sekund·arwicklung w·ahrend dieser stromleitenden Phase stark belastet, z.B. ·uber den Thyristor kurzgeschlossen wird, bricht auch die Spannung an der prim·arseitigen R·uckkopplungswicklung zusammen. Diese Wicklung kann dann f·ur den Schalttransistor nicht mehr einen f·ur den leitenden Betrieb ausreichenden Basis strom liefern. Das Schaltnetzteil schwingt dann nicht mehr, so dass die sekund·arseitigen Betriebsspannungen in erw·unschter Weise zusammenbrechen. Der schaltungstechni- sche Aufwand ist gering. Er besteht vorzugsweise aus einem Thyristor und zwei Widerst·anden.
Ein Ausf·uhrungsbeispiel der Erfindung wird anhand der Zeichnung erl·autert. Darin zeigen Figur 1 ein erfindungsgem·ass ausgebildetes Schaltnetzteil und Figur 2 Kurven zur Erl·auterung der Wirkungsweise. Dabei zeigen die kleinen Buchstaben, an welchen Punkten in Figur 1 die Spannungen gem·ass Figur 2 stehen.
Das Schaltnetzteil gem·ass Figur 1 enth·alt auf der Prim·arseite des Trenntransformators 1 den Netzgleichrichter 2, den Ladekondensator 3, den Strom-Messwiderstand 4, die Prim·arwicklung 5 den Schalttransistor 6, die zur Schwingungserzeugung dienende R·uckkopplungswicklung 7, den zur Steuerung des Schalttransistors 6 dienenden Thyristor 8, die Regelwicklung 9, den zur Erzeugung der Regelspannung dienenden Gleichrichter 10 sowie die zur Stabilisierung der Betriebsspannungen dienende Regelschaltung 11 mit dem Transistor 12 und der eine Referenzspannung lieferndenZenerdiode 13. Die Sekund·arwicklung 14 liefert ·uber den Gleichrichter 15 eine erste Betriebsspannung U1 von 150 V. Ein Abgriff der Wicklung 14 liefert ·uber den Gleichrichter 16 eine zweite Betriebsspannung U2 von 12 V f·ur einen Fernbedienungsempf·anger.
Eine weitere Sekund·arwicklung 19 liefert ·uber den Gleichrichter 20 eine dritte Betriebsspannung U3 von 12 V. Die Polung der Wicklungen 14,19 und der Gleichrichter 15,16,20 ist derart, dass die Gleichrichter 15,16,20 w·ahrend der Sperrphase des Schalttransistors 6 durch die sekund·arseitig auftretenden Impulsspannungen leitend gesteuert sind und die angeschlossenen Ladekondensatoren aufladen.
An das untere Ende der Wicklung 19 ist zus·atzlich der Thyristor 24 angeschlossen. An die Steuerelektrode b des Thyristors 24 ist die Betriebs spannung U2 ·uber den Spannungsteiler 25,26 angelegt.
Die Wirkungsweise der Schaltung wird anhand der Figur 2 erl·autert. Es sei angenommen, dass das Schaltnetzteil im Zeitpunkt tl in Betrieb genommen wird. Mit der Diode 21 wird aus der Netzspannung am Punkt d ein positiver Impuls erzeugt. Dieser gelangt ·uber den Kondensator 23 auf die Basis des Schalttransistors 6 und steuert diesen leitend. Dadurch beginnt das Schaltnetzteil zu schwingen, wobei die Schwingung durch die R·uckk
opplungswicklung 7
aufrechterhalten wird. Am Punkt a entsteht dann eine m·aanderf·ormige
Wechselspannung mit einer Frequenz von etwa 25-30 kHz.Die daraufhin in den Sekund·arwicklungen 14,19 erzeugten Impulse erzeugen in der beschriebenen Weise die Betriebsspannungen U1,U2,U3. Der Spannungsteiler 25,26 ist so bemessen, dass der Thyristor 24 gesperrt bleibt, d.h. die Spannung am Punkt 6 jst kleiner als 0,7 V. Der Thyristor 24 hat dann keine Wirkung. Dir Amplitude der Spannungen Ui,U2,U3 wird ·uber die Regelschaltung 11 stabilisiert.
Es sei jetzt angenommen, dass durch einen Fehler in der Regelschaltung 11, z.B. durch Ausfall eines Bauteiles, die Regelung zur Stabilisierung der Betriebsspannungen U1,U2,U3 nicht mehr wirkt und diese Betriebsspannungen stark ansteigen. Dadurch steigt auch die Spannung am Punkt b an.
Im Zeitpunkt t2 erreicht diese Spannung den Wert von 0,7 V, so dass der Thyristor 24 z·undet. Der untere Teil der Wicklung 19 ist jetzt praktisch kurzgeschlossen. Das Netzteil ist dadurch sekund·arseitig so stark belastet, dass die R·uck kopplungswicklung 7 keinen ausreichenden Basisstrom zur Steuerung des Schalttransistors 6 in seine stromleitende Phase mehr liefert. Im Zeitpunkt t2 bricht die Schwingung des Schaltnetzteiles ab, so dass auch die Wechselspannung am Punkt a auf null abf·allt. Den Ladekondensatoren der Gleichrichter 15,16,20 wird kein Strom mehr zugef·uhrt, so dass die Betriebspannungen U1,U2,U3 nicht weiter ansteigen k·onnen, sondern entsprechend den wirksamen Entladezeitkonstanten abfallen. Das Schaltnetzteil w·urde auf diese Weise an sich beliebig lange ausgeschaltet bleiben.
Im Zeitpunkt t3 erscheint am Punkt b der n·achste aus der Netzspannung gewonnene Startimpuls, der den Schalttransistor 6 wieder leitend steuert, so dass die Wechselspannung am Punkt a wieder auftritt. Das Schaltnetzteil geht also in einen getakteten Betrieb ·uber, bei dem die ·ubertragene Leistung entsprechend dem Zeitverh·altnis zwischen Einschaltphase und Ausschaltphase der Spannung am Punkt a betr·achtlich verringert ist. Die Betriebsspannungen U11U2,U3 k·onnen nicht mehr unzul·assig hohe Werte annehmen.
- BS395.1 LINE DEFLECTION OUTPUT UNIT WITH BU208A (MOTOROLA) This p.c.b. amplifies the pulse sequence at line frequency and drives a circuit operating asan ON-OFF switch for supplying the deflection current to the horizontal yoke. It also
receives the parabolic signal which acts on the diodes modulator for E/W correction.
- BS396.3 SYNCHRONIZATION + E/W CORRECTION The p.c.b. processes the videosignal. Said process consists in separating the horizontal signals from the video composite
signal. The "pincushion correction" section receives a Sawtooth shaped signal and converts it into a parabolic shape for E/W correction.
- BS397.1 FRAME DEFLECTION WITH TDA1170 This p.c.b. generates a sawtoothvoltage at frame frequency which is used for driving the vertical deflection yoke. It supplies a
similar voltage to the "pincushion" section of the synchro. separator p.c.b. to obtain the E/W pincushion correction. It supplies a frame frequency pulse which is used for the luminance, chrominance and video amplifier p.c.b. blankings. It receives the vertical synchro.
from the synchro. separator p.c.b. and receives from the chassis a voltage proportional to the beam current.TDA1170 vertical deflection FRAME DEFLECTION INTEGRATED CIRCUITGENERAL DESCRIPTION f The TDA1170 and TDA1270 are monolithic integrated
circuits designed for use in TV vertical deflection systems. They are manufactured using
the Fairchild Planar* process.
Both devices are supplied in the 12-pin plastic power package with the heat sink fins bent
for insertion into the printed circuit board.
The TDA1170 is designed primarily for large and small screen black and white TV
receivers and industrial TV monitors. The TDA1270 is designed primarily for driving
complementary vertical deflection output stages in color TV receivers and industrial
monitors.
APPLICATION INFORMATION (TDA1170)
The vertical oscillator is directly synchronized by the sync pulses (positive or negative); therefore its free
running frequency must be lower than the sync frequency. The use of current feedback causes the yoke
current to be independent of yoke resistance variations due to thermal effects, Therefore no thermistor is
required in series with the yoke. The flyback generator applies a voltage, about twice the supply voltage, to
the yoke. This produces a short flyback time together with a high useful power to dissipated power
ratio.
- BS399.0 LUMINANCE AND CHROMINANCE + RGB AMPLIFIER This p.c.b. processes thecomplete composite video signal coming from the IF p.c.b. andsupplies the R-G-B signals to
the picture tube.
- BS398 TUNER + AFC + IF Conversion of the RF signal into an IF signal(video carrier:39.5 M z; audio carrier:33.5 MHZ).
Detection of the IF signal into low frequency video and audio signals.
- BS389 REMOTE CONTROL DECODER WITH ITT SAA1251 This p.c.b. enables remotecontrol of the following functions: selection of 16 programmes; "+" or "-" adjustment; brightness
saturation adjustment; silencing; TV receiver switching.
- BS388.2 TUNING MEMORY AND SEARCH Remote control p.c.b. The display indicates the programme selected. Furthermore,this p.c.b. includes all pushbuttons for clockadjustment.No adjustments needed. Automatic searching of a TV station through a start command. Manual searching of a TV station through two commands (increment and decrement).
Inclusion-exclusion of the AFC circuit with LED display. Band indication displayed on
three LEDs. Tuning level indication with five LEDs. Memorization of 16 selected
programmes manually or remote control.
- BS392.2 ST-BY SUPPLY AND OPTOCOUPLER START STOP FEATURE. The p.c.b. includes circuits relevant to: mains filter, degaussing, remote control supply, start remote control.Nc adjustments needed. It includes circuits for clock supply and for switch-ON
programming.
- BS401 This p.c.b. receives the audio signal (not adjusted in volume) coming from p.c.b. BS 398, it adjusts it in amplitude and tone, it amplifies it and sends it to drive the two receiver’s loudspeakers (tweeter and woofer).
BU208A (MOTOROLA). Silicon NPN
npn transistors,pnp transistors,transistorsCategory: NPN Transistor, Transistor
MHz: <1 MHz
Amps: 5A
Volts: 1500V
HIGH VOLTAGE CAPABILITY
JEDEC TO-3 METAL CASE.
DESCRIPTION
The BU208A, BU508A and BU508AFI are
manufactured using Multiepitaxial Mesa
technology for cost-effective high performance
and use a Hollow Emitter structure to enhance
switching speeds.
APPLICATIONS:
* HORIZONTAL DEFLECTION FOR COLOUR TV With 110° or even 90° degree of deflection angle.
ABSOLUTE MAXIMUM RATINGS
Symbol Parameter Value Unit
VCES Collector-Emit ter Voltage (VBE = 0) 1500 V
VCEO Collector-Emit ter Voltage (IB = 0) 700 V
VEBO Emitter-Base Voltage (IC = 0) 10 V
IC Collector Current 8 A
ICM Collector Peak Current (tp < 5 ms) 15 A
TO - 3 TO - 218 ISOWATT218
Ptot Total Dissipation at Tc = 25 oC 150 125 50 W
Tstg Storage Temperature -65 to 175 -65 to 150 -65 to 150 oC
Tj Max. Operating Junction Temperature 175 150 150 °C
SELECO (ZANUSSI) 22ST303 "BIG" CHASSIS BS400 Television receiver with an automatic station finding arrangement:
The present invention relates to a television tuning device, comprising a circuit for continuously scanning at least one band of receivable frequencies, and having control means for starting and stopping the said scanning procedure and a terminal for applying a switch signal for switching from a first band-scanning speed to a second band-scanning speed slower than the first.
The name usually applied to a unit consisting of circuits of this type for selecting and memorising a given number of preferred channels is "station memory".
Many types of station memories are already being sold on the market which can be divided into two main groups: those with automatic and those with manual television channel searching.
The automatic types are fitted with electronic searching circuits which locate television channels automatically when started by the user. This is done by scanning a given band (VHF or UHF, for example) and stopping on the located channel. Data relative to the located channel can then be memorised by the user in a memory circuit and the same channel recalled whenever required by simply pressing a button which recalls the said data from the memory and supplies it to the channel selection circuit.
This type of circuit is also fitted with components which sense, during search, if a television channel has been tuned into and disable automatic searching to prevent television band scanning from continuing. Most of these circuits are fitted with a phase detector which senses the coincidence between the sync signals received and those regenerated in the receiver (in particular, the flyback signal).
Manual station memories, on the other hand, are fitted with controls which, when activated by the user, start a device for scanning a given television band. These controls also stop the said device when required by the user. When the user sees the required channel appear on the screen, the device is stopped to disable search and enable the channel to be memorised in the appropriate circuit.
In these cases, the simplest way of starting and stopping the search is to fit the circuits with a button which, when pressed, supplies a search-start signal and, when released, stops the searching operation. For best tuning, two buttons are usually provided for band scanning in both directions.
Both the types discussed up to now present drawbacks. In the case of automatic station memories, for example, tuning quality depends on correct operation of all the search-stop circuits and the automatic tuning circuit (AFC=automatic frequency control). Even in cases where these circuits are operating correctly, tuning could still be impaired by noise or amplitude distortion on the received signal.
Tuning quality on manual station memories, on the other hand, depends on the tuning ability of the user. Television receivers can be manipulated by anybody not all of whom are gifted with this ability. A further drawback of manual station memories is that the user has very little time in which to decide whether the received channel is the right one and to estimate tuning quality. If the whole television band is to be scanned in a reasonable length of time (let us say, the UHF band in one minute) band-scanning speed needs to be fairly high. Consequently, if the user is not quick enough in sending out the search-stop control signal, it is more than likely that the control will be sent when the required television channel has been overshot. If, by chance, there are two channels close to one another, the searching device may even stop on the second of the two, thus confusing the user who will not know which of the two channels he has tuned into.
The aim of the present invention is to provide a tuning device to overcome these problems.
With this aim in view, the present invention provides a television tuning device comprising a circuit for continuously scanning at least one band of receivable frequencies, manual control means for starting and stopping the said scanning procedure, a terminal for applying a switch signal for switching from a first band-scanning speed to a second band-scanning speed lower than the first, and detection means for detecting the presence of a television channel by comparing the received sync signals with local signals generated in the television receiver, and applying a switch signal to the said terminal for switching from the said first scanning speed to the said second scanning speed in the presence of the said switch signal, so that the band scanning continues at said lower speed until the manual control means produce the stopping scanning procedure.
MOTOROLA TUNING MEMORY / MEMOTRONIC SYSTEM TECHNOLOGY.In a radio or television receiver containing an automatic station finder with a digital counter, a clock generator, and a digital-to-analog converter forming the tuning voltage for the varactors, a recall memory consisting of two series-connected parallel memories is connected in parallel with the digital counter. At a stop signal from the
1. A receiver having automatic station finding capability, comprising:
means for tuning said receiver in response to an applied voltage;
a controllable pulse generator;
means for starting said pulse generator;
circulating counter means having parallel inputs and outputs, a stepping input and a set input, said stepping input connected to and responsive to pulses from said pulse generator for providing a variable digital output;
digital-to-analog convert
means for sensing a received signal and for providing a stop signal to the pulse generator in response thereto, whereby said generator stops providing pulses and the analog voltage remains constant keeping the receiver tuned to the received signal;
memory means having parallel inputs connected to the parallel outputs of said counter means and parallel outputs connected to the parallel inputs of said counter means;
means associated with said memory means for causing the memory means to store a particular digital output from said counter means; and
means associated with the set input of said counter means for selectively causing the digital signal at the counter input to be transferred to the counter output.
2. A receiver as described in claim 1, wherein the memory means comprises: two series connected parallel memories each having a transfer input, a first of said parallel memories having parallel inputs connected to the parallel outputs of the counter means and having the transfer input connected to the stop signal means, a second of said parallel memories having parallel outputs connected to the parallel inputs of the counter means and having the transfer input connected to the means for starting said pulse generator.
3. A receiver as described in claim 2, wherein each of said parallel memories comprises a plurality of semiconductor voltage flip-flops.
4. A receiver as described in claim 2, wherein the two series connected parallel memories are incorporated in an integrated circuit module with the counter means.
5. A receiver as described in claim 2, wherein the transfer input of the first parallel memory is also connected to the means associated with the set input of the counter means.
6. A receiver as described in claim 1, additionally comprising:
an additional memory means having parallel inputs and outputs;
means for connecting the inputs of said additional memory means to the counter means output and the outputs of said additional memory means to the counter inputs;
means for causing said additional memory means to store a digital output; and
means for transferring the stored digital output to the counter means input through the connecting means.
7. A receiver as described in claim 6, additionally comprising gate means disposed at the outputs of the memory means and the additional memory means for selectively connecting either the additional memory means or the memory means to the input of the counter.
8. A receiver as described in claim 6, wherein the additional memory means comprises a plurality of memories and the connecting means comprises a plurality of station switches corresponding in number to the number of additional memories.
9. A receiver as described in claim 1, wherein each memory means comprises a number of flip-flops corresponding to the number of digits to be stored.
Such a radio receiver is known from, e.g., the journal "Funkschau 1971", pp. 535 to 538 and 587 to 589. With the aid of the free-running pulse generator, the up-counter, and the digital-to-analog converter, the automatic station finding arrangement generates a sawtoothlike tuning voltage for the varactors contained as frequency-setting tuning elements in the resonant circuits of the receiver's radio-frequency portion. If a transmitter is received which meets the receiving criteria set in the receiver, the pulse generator is stopped so that the tuning voltage now remains constant until the operator continues the automatic station finding operation by actuating a start switch.
It is frequently desirable to tune in once again the station at which the start switch for automatic station finding was actuated last - either for comparison or because of the more interesting program. To do this in the case of a receiver with provision for unidirectional automatic station search, the entire search range must be scanned once or several times by repeatedly actuating the start switch, depending on whether the desired station is detected immediately or not.
It is the object of the invention to provide measures for a receiver of the kind referred to by way of introduction which permit the transmitter received before the actuation of the start switch to be found again with a high degree of safety by simple manipulation.
The invention is characterized in that the parallel memory consists of two series-connected parallel memories having one transfer input each, that the transfer input of the (first) parallel memory, whose parallel inputs are connected to the parallel outputs of the counter, are connected directly or indirectly to the stop line, that the transfer input of the (second) parallel memory, whose parallel outputs are connected to the parallel inputs of the counter, is connected directly or indirectly to the start line, that the counter has a set input for through-connecting the parallel inputs of the counter to the flip-flops of the counter, and that a recall switch is connected to the set input of the counter.
Particularly advantageously, the memory locations of the two series-connected parallel memories are storage flip-flops using semiconductor technology. In that case it is possible to arrange the counter and the parallel memories on a common chip of an integrated-circuit module. Such a module has only two terminals more than a module formed by the counter only.
The measures characterized by the invention thus require, aside from an additional recall switch, no additional space and involve nearly no additional expense. To recall the station previously tuned in it is only necessary to depress a button, for example, whereby the receiver is safely tuned to the station's carrier wave even if at the instant of the depression the local received field strength is temporarily too low for sufficient reception.
The invention will now be described in more detail with reference to the accompanying drawing, showing, by way of example, two embodiments of the invention, and wherein:
FIG. 1 is a block diagram showing the radio- and intermediate-frequency portions of a receiver with an automatic station finding arrangement and a recall arrangement;
FIG. 2 shows diagrams a to g explaining the operation of the recall storage, and
FIG. 3 shows a receiver similar to the one of FIG. 1 in which the automatic station finding counter and the recall memories are arranged together on the chip of an integrated-circuit module.
The receivers shown in the block diagrams of FIGS. 1 and 3 have a radio-frequency-receiving section 1, an intermediate-frequency amplif
ier 2, and a demodulator section 3, to whose output 4 are connected the arrangements processing the modulation frequency. The tunable resonant circuits of the radio-frequency section contain varactors as tuning elements. Connected to the radio-frequency section is an automatic station finding arrangement in which a digital-to-analog converter 5 generates from the count of a digital counter 7, which receives signals at a stepping input T and advances at the rate of a pulse generator 6, a nearly sawtooth-shaped tuning voltage for the varactors. With a sufficient received field strength at the antenna 8 of the receiver a signal is formed in the demodulator section 3 which signal can be used as stop signal 9 to change the state of a start-stop circuit 10 which may be a flip flop. In the "stop" state the start-stop circuit interrupts the pulse generation or the pulse flow in the pulse generator so that the receiver remains tuned to the station being received. By operating a start-button switch 11 a start signal 12 is generated in the receiver which signal places the start-stop circuit in the "automatic station finding" state and thus continues the automatic station finding operation until next station meeting the receiver's receiving requirements is received. In the embodiment of FIG. 1, two series-connected parallel memories 15 and 16 are connected, respectively, over two groups of lines 13 and 14 consisting of n lines each, between the n outputs Q 11 to Q n1 and the parallel inputs A 11 to A n1 of the digital counter 7 containing n counting flip-flops. Each parallel memory contains n storage flip-flops and, besides the parallel bit inputs and outputs B and X, a transfer input S. If a transfer signal appears at the transfer input, the parallel memory records the bit word applied its parallel inputs B 1 to B n , which erases the previously entered bit word and now, in turn, appears at the memory outputs X 1 to X n .
The transfer input S of the parallel memory 15, whose parallel inputs are connected over the group of lines 13 to the outputs of the counter 7, is connected to the stop line 17, while the transfer input S of the parallel memory 16, whose parallel outputs are connected over the group of lines 14 to the parallel inputs of the counter 7, is connected to the start line 18.
Connected to a set input P of the digital counters 7 is a switch 19 whose operation generates a set signal. The set signal sets the counter to a count which is equal to the bit word at the parallel inputs A 1 to A n of the counter. At the same time, the set signal acts over the line 20 and via an OR circuit provided for isolation on the transfer input S of the first parallel memory 15.
The diagrams a to g of FIG. 2 explain the operation of the automatic station finding arrangement in conjunction with the recall memories. In diagram a each of the blocks II, III, etc. represents the bit word for a count of the digital counter 7. The blocks in the diagrams b and c are the bit words which are stored in the parallel memories 15 and 16 and can be taken off the latter's parallel outputs, the blocks with equal Roman numerals (e.g. V) representing equal bit words. The diagram d shows the counting pulses 22 for the digital counter 7, the diagram e the stop pulses 9, the diagram f the start pulses 12, and the diagram g the set pulse 23 triggered by the recall switch 19.
The respective count from which the digital-to-analog converter 5 forms the tuning voltage for the varactors is applied simultaneously to the input of the digital-to-analog converter and, as a bit word (e.g. II, III, IV . . . , diagram a), to the input of the first parallel memory 15. At the occurence of a stop signal 9 during the automatic station finding operation, the stop signal 9 acts as a transfer signal on the first par
If the operator operates the recall switch 19 so as to recall the setting to the previously received station, the set pulse 23 triggered by the recall switch sets the counter 7 to the count (e.g. V, diagram a) of the bit word (e.g. V, diagram c) stored in the second parallel memory 16, and the newly set count is entered into the first parallel memory 15 (e.g. V, diagram b). The next start signal (e.g. 12b, diagram f) initiates the automatic station finding operation as described.
In the embodiment of FIG. 3, the two series-connected parallel memories 15 and 16 are incorporated on the chip of an integrated-circuit module 25 which also comprises the circulating digital counter 7 and, for exam
ple, the circuit 26 of a station memory device. The station memory device has the memory inputs D 1 to D n and the memory outputs Y 1 to Y n of its circuit 26 connected in parallel with the digital counter 7 in the same manner as the recall memory consisting of the two series-connected parallel memories 15 and 16. Therefore, gate circuits 27 and 28 are inserted between the parallel outputs of these memories and the parallel inputs A 1 to A n of the digital counter. The gate circuit 27 between the recall memory and the counter is opened by the set signal of the recall switch 19. The gate circuit 28 between the station memory and the counter is opened by the set signal of a switch 29 for calling the bit word of a station preselected by the station buttons 30. In front of the set input 8 of the digital counter the two set signals are separated from one another in an OR circuit 31. In the embodiment of FIG. 3, the start-stop circuit 10 is designed in the manner of a flip-flop and can assume a "stop" state and an "automatic station finding" state. The transfer inputs S of the recall memory's parallel memories 15 and 16 are connected via the lines 32 and 33 to the outputs of the start-stop circuit. Since the signals at the outputs of the start-stop circuit are continuous signals, the lines 32 and 33 to the transfer inputs include pulse shapers 34 and 35, respectively.
In embodiments corresponding to FIG. 3 and having no station memory device, besides the circuit 26, the gate circuits 27 and 28 and the OR circuit 31 are omitted.
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