Toshiba 29V24F, Service Manual

Page: 5 / 91

4
2.6 Chroma and luminance processing:
The chroma decoder is able to demodulate PAL, NTSC and SECAM signals.
The decoder dedicated to PAL and NTSC sub-carrier is based on a synchronous demodulator, and an Xtal PLL locked on
the phase reference signal (burst).
The SECAM demodulation is based on a PLL with automatic calibration loop.
The color standard identification is based on the burst recognition.
Automatic and forced modes can be selected through the I
2
C bus.
NTSC tint, and auto flesh are controlled through I
2
C bus.
Xtal PLL can handle up to 3 crystals to work in PAL M, PAL N and NTSC M for South America.
ACC an ACC overload control the chroma sub-carrier amplitude within 26dB range. Both
ACC s are based on digital systems and do not need external capacitor.
All chroma filters are fully integrated and tuned via a PLL locked on Xtal VCO signal.
A second PLL is used for accurate fine-tuning of the SECAM bell filter. This tuning is achieved during the frame blanking.
An external capacitor memorizes the bell filter tuning voltage.
A base-band chroma delay-line rebuilds the missing color line in SECAM and removes transmission phase errors in PAL.
The base-band chroma delay line is clocked with 6MHz signal provided by the horizontal scanning VCO.
The luminance processor is composed of a chroma trap filter, a luminance delay line, a peaking function with noise
coring feature, a black stretch circuit.
Trap filter and luminance delay lines are achieved with the use of bi-quad integrated filters, auto-aligned via a master
filter phase locked loop.
2.7 RGB output circuit:
The video processor performs the R, G, B processing.
There are three sources:
1. Y,U,V inputs (coming from luma part (Y output), and chroma decoder outputs (R-Y, B-Y outputs).
2. External R,G,B inputs from SCART (converted internally in Y,U,V), with also the possibility to input YUV signals from
a DVD player, (YUV specification is Y=0.7 V PP , U= 0.7 V PP , V = 0.7V PP for 100% color bar).
3. Internal R,G,B inputs (for OSD and Teletext display)
The main functions of the video part are:
• Y,U,V inputs with integrated clamp loop, allowing a DC link with YUV outputs,
• External RGB inputs (RGB to YUV conversion), or direct YUV inputs,
• Y,U,V switches,
• Contrast, saturation, brightness controls,
• YUV to RGB matrix,
• OSD RGB input stages (with contrast control),
• RGB switches,
• APR function,
• DC adjustment of red and green channels,
• Drive adjustments (R, G, B gain),
• Digital automatic cut-off loop control,
• Manual cut-off capability with I
2
C adjustments,
• Half tone, oversize blanking, external insertion detection, blue screen,
• Blanking control and RGB output stages.
2.8 µ-Controller
The ST92195 is the micro-controller, which is required for a color TV receiver. ST92195D1 is the version with one page
Teletext and ST92195D7 is the one with 7 page Teletext. The IC has the supply voltages of 5 V and they are mounted in
PSDIP package with 56 pins.
µ-Controller has the following features
• Display of the program number, channel number, TV Standard, analogue values, sleep timer, parental control and mute
is done by OSD
• Single LED for standby and on mode indication
• System configuration with service mode
• 3 level logic output for SECAM and Tuner band switching