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Principles of Operation
Page 5-4
Service Manual
MT930B
VIDEO BACK PORCH CLAMPING
When back porch clamping is selected, QM10 is turned on during the back porch
interval, and back porch clamping is performed. LV01 and CV26 form a trap to
prevent any adverse effect on the burst signal.
VIDEO CLAMPING OFF
When neither sync-tip nor back porch clamping are selected, QV07 is turned on
to allow transfer down to extremely low frequencies.
VIDEO BUFFER AMPLIFIER
The MT930B includes three video outputs, each equipped with a buffer amplifier.
This is so a short occurring at a given output terminal will not adversely affect the
other output terminals.
VIDEO LEVEL CONTROL INTERFACE
QJ03 is capable of producing a stable 1.2 V reference voltage. QJ01 is an 8-bit
electric potentiometer capable of driving the reference voltage. QJ02 is a DC
level shifter that converts the voltage to that required by QV06 and QG02.
AUDIO IF CONVERTER
The output signal of the 70 MHz detector (including an audio subcarrier) is input
to JB01. QB11 and QB71 are frequency-converter ICs. The audio subcarrier can
be converted to 10.7 MHz by generating a local 10.7 MHz higher that the desired
audio subcarrier, The comparison frequency is 5 kHz.
AUDIO IF FILTER
Audio #1 includes a built-in three-band BPF, while Audio #2 and #3 include built-
in five-band BPFs. The 880 kHz BW uses and LC filter, while the 55 kHz BW
uses a combination of crystal and ceramic filters. Ceramic filters are used for the
other BW filters.
AUDIO DETECTOR
QA11, QA41, and QA71 are FM-detect ICs used to extract the audio signal by
detecting the 10.7 MHz audio subcarrier.
AUDIO SLIDING DE-EMPHASIS
Sliding de-emphasis Audios #2 and #3 can be used. Q901 does RMS value de-
tection, while Q902 performs expansion. QE01 is an audio amplifier that per-
forms boosting for level compensation when 110 kHz BW or 55 kHz BW are
used.
AUDIO DE-EMPHASIS
It is possible to select one of four types of de-emphasis: 50
µ
sec, 75
µ
sec, J17,
or Flat. A transistor is used for switching.
Содержание mt930b
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Страница 90: ...Drawings Page 9 2 Service Manual MT930B 10264 Figure 9 1 MT930B Block Diagram 1 ...
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Страница 93: ...Drawings MT930B Service Manual Page 9 5 10267 Figure 9 4 MT930B Block Diagram 4 ...
Страница 94: ...Drawings Page 9 6 Service Manual MT930B 10268 Figure 9 5 MT930B Head Phone Schematic ...
Страница 95: ...Drawings MT930B Service Manual Page 9 7 10269 Figure 9 6 MT930B RF PC Board Schematic ...
Страница 96: ...Drawings Page 9 8 Service Manual MT930B 10270 Figure 9 7 MT930B Converter Module Schematic ...
Страница 97: ...Drawings MT930B Service Manual Page 9 9 10271 Figure 9 8 MT930B Main PC Board Sheet 1 of 3 ...
Страница 98: ...Drawings Page 9 10 Service Manual MT930B Figure 9 9 MT930B Main PC Board Sheet 2 of 3 ...
Страница 99: ...Drawings MT930B Service Manual Page 9 11 10273 Figure 9 10 MT930B Main PC Board Sheet 3 of 3 ...
Страница 100: ...Drawings Page 9 12 Service Manual MT930B 10274 Figure 9 11 MT930B Power Supply Schematic ...
Страница 101: ...Drawings MT930B Service Manual Page 9 13 10275 Figure 9 12 MT930B IF Filter Block Schematic ...
Страница 102: ...Drawings Page9 14 Service Manual MT930B 10276 Figure 9 13 MT930B Audio IF PB01 Schematic ...
Страница 103: ...Drawings MT930B Service Manual Page 9 15 10277 Figure 9 14 MT930B Audio Out Schematic ...
Страница 104: ...Drawings Page 9 16 Service Manual MT930B 10278 Figure 9 15 MT930B Audio PW01 PC Board Schematic ...