Loewe Q2500B Serviceanleitung Seite 126

Technology of Q 2500 colour TV set
1 Introduction ..............................................5
1.1 Foundations of 100 hz technology ................ 7
1.1.1 Prerequisites for 100 Hz ........................ 7
1.1.2 100 Hz display modes ........................... 7
1.1.3 Mode AABB ......................................... 7
1.1.4 Mode ABAB ......................................... 9
1.1.5 Mode AA'B'B....................................... 9
1.1.6 Mode AA*BB* ..................................... 9
2 Basic board............................................12
2.1 Standby power supply ................................. 12
2.1.1 Standby power supply circuit .............. 12
2.2 Blocking oscillator type power supply ........ 13
2.2.1 Primary side......................................... 14
2.2.2 Start-up................................................ 16
2.2.3 Normal and control operation.............. 16
2.2.4 Protective operation............................. 17
2.2.5 Power Factor Control .......................... 17
2.2.6 Secondary side..................................... 18
2.2.7 Voltage stabilisation ............................ 20
2.2.8 Voltage increase .................................. 20
2.2.9 Servicing information.......................... 21
2.3 Horizontal deflection and high voltage
production ............................................................... 21
2.3.1 Horizontal driver ................................. 21
2.4 Horizontal output stage ............................... 22
2.4.1 High voltage production...................... 25
2.4.2 Horizontal- offset deflector ................. 25
2.5 East/west correction .................................... 26
2.5.1 Circuit.................................................. 27
2.6 Vertical output stage.................................... 28
2.6.1 Flyback generator ................................ 29
2.6.2 Vertical protective circuits .................. 30
2.7 Beam current limitation............................... 32
2.7.1 Overbeam current fuse ........................ 33
2.7.2 HFLB protective circuit....................... 34
2.8 Speed modulator.......................................... 34
2.8.1 General ................................................ 34
2.8.2 Switching of the speed modulator ....... 36
2.9 Colour stages............................................... 37
2.9.1 Cut off control ..................................... 38
2.9.2 Switch off flash suppression................ 40
2.10 Rotation panel ............................................. 40
2.10.1 Raster correction ................................. 40
2.10.2 Circuit.................................................. 41
2.11 NF output stages.......................................... 42
3 Receiver components ............................44
3.1 HF/IF unit.................................................... 44
3.1.1 HF/IF components............................... 44
3.2 DVB Board.................................................. 46
3.2.1 Overview ............................................. 46
3.3 Features and parameters .............................. 48
3.3.1 DVB internal features.......................... 48
3.3.2 DVB/TV-Features ............................... 52
3.3.3 Architecture......................................... 52
3.4 Components................................................. 54
3.4.1 Satellite front end ................................ 54
3.4.2 Functional distribution ........................ 54
3.4.3 Tuner ................................................... 54
Document Q 2500
3.4.4 DVB demodulation and fault correction
56
3.4.5 LNC supply..........................................59
4 Signal board .......................................... 60
4.1 Device control..............................................60
4.1.1 The infrared sensor...............................62
4.1.2 Infrared receiver...................................65
4.1.3 The SDA 6000 central control unit ......66
4.1.4 Reset.....................................................67
4.1.5 Creation of cycle frequency .................68
4.1.6 Operational commands.........................68
4.1.7 LED display .........................................68
4.1.8 ON/OFF function .................................68
4.1.9 Protective circuit ..................................68
4.1.10 AV operation........................................69
4.1.11 SAT standby.........................................70
4.1.12 SAT unit control...................................71
4.2 Bus systems in Q 2500 chassis.....................72
4.2.1 I²C bus systems ....................................73
4.2.2 IC 24C64 memory................................75
4.2.3 EPROM M 27 C 322............................75
4.2.4 SRAM ..................................................76
4.2.5 Search functions...................................76
4.2.6 Storage .................................................76
4.2.7 Programme recall .................................76
4.2.8 System clock ........................................77
4.2.9 Control of signal processing.................77
4.2.10 Service mode........................................78
4.2.11 Video text.............................................78
4.2.12 Picture signal processing......................78
4.2.13 Components for....................................79
4.2.14 Signal path ...........................................80
4.2.15 IC functions..........................................84
4.3 VPC 3230.....................................................84
4.3.1 Input interface ......................................85
4.3.2 20.25 MHz clock generator..................86
4.3.3 Comb filter ...........................................87
4.3.4 Multi-standard colour decoder .............89
4.3.5 Line compression and .........................89
4.3.6 Output format conversion ....................90
4.3.7 Synchronisation block..........................90
4.3.8 I²C bus interface ...................................90
4.4 Half picture memory SAA4955HL ..............90
4.4.1 Storage space........................................91
4.4.2 Conversion of signals in.......................92
4.4.3 Half picture memory 2 and 3 ...............92
4.4.4 Control pulses ......................................92
4.5 Falconic module SAA 4993 .........................96
4.5.1 Noise reduction ....................................96
4.5.2 Line interpolation.................................98
4.5.3 Movement detector ..............................99
4.5.4 Memory control....................................99
4.6 SAA 4979 (BESIC)......................................99
4.6.1 Chroma branch...................................100
4.6.2 Band width doubling ..........................101
4.6.3 Colour flank sharpening....................101
4.6.4 Y signal path ......................................101
4.6.5 Microprocessor interface....................102
4.6.6 Control of the 100 Hz processing.......102
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