Table of Contents
Advertisement
3. Analog Board Europe (A, B, G models)
3.1 Microprocessor TMP93C071F
The microcontroller „AIO" TMP93C071F is a 16bit
microcontroller with internal ROM and 8kB RAM. It
includes the
following functions:
• A/D converters
• composite sync input
2
• I
C bus interface
Following connection to the mains, a positive pulse on the
reset input on the P is generated by the reset-IC TL7705
(Pos.7900).
The system clock is generated with the 20MHz quartz
(Pos. 1994).
3.2 Bus Systems
The communication between the P and the other
functional groups is via the I
2
C-bus (SDA, SCL). The clock
rate is approx. 95kHz.
2
Functional groups on the I
C bus:
• E
2
PROM ST24E16 (Pos. 7815)
• Tuner (Pos. 1705)
• Matrix-switch STV6410 (Pos. 7507)
• Audio IC / MSP (Pos. 7600)
• Display board (Pos. 1987)
• VPS-IC (Pos. 7990).
2
3.3 E
PROM
The E
2
PROM ST24E16 (Pos. 7815) is an electric erasable
and programmable, non-volatile memory. The E
stores data specific to the device, such as the AFC-
reference value, clock-correction- factor, etc. The data is
2
accessed by the P via the I
C-bus.
3.4 VPS, PDC, Teletext (Europe Only)
The STV5348 (Pos. 7990) is a VPS, PDC, and Teletext
Decoder with an external 13,875Mhz quartz.
The following data formats are identified:
• VPS (Timer data and station name)
• PDC Format 2 (Timer data and station name)
• PDC Format 1 (station name and time)
• TXT header line (time for „time download")
3.5 FOME
The FOME-circuit compares the video signal coming from
the tuner and the one coming from the Scart-plug 1. If the
video-signals are identical the output of the FOME-circuit
is low.
3.6 Fan Control
The fan control circuit is necessary to control the speed of
the cabinet fan (Pos. 1984) according to the requirements
in temperature and noise. The temperature is measured
via an NTC on the display board (Pos. 3145). When the
temperature is lower than 25° C the fan-voltage is approx.
5V and will reach approx. 10V at a temperature of 40° C. It
is also possible to switch off the fan via the control line
ION_FAN. The circuit generates also two control-signals:
TEMP goes to the P and BE_FAN is the control-line for the
basic engine fan.
3.7 Power Supply
The 5SW and 8SW supply are switched off in case of
standby from the P via the ISTBY-line. This is possible for
power-save.
The ISTBY-line must be low in case of STBY. There is also
a „power fail" circuit on the PS-schematic which is
necessary to mute AUDIO when IPFAIL is low.
3.8 Front End (TU, AP Part)
The Front End Comprises the Following Parts:
• Tuner [1705]
• IF amplifier & video demodulator IC TDA 9818 [7703]
• Sound processor MSP3415G [7600]
IF Selection
The IF frequency of the video carrier is 38.9 MHz for all
systems except SECAM L' (33.9 MHz).
A quasi-split audio system is used. Separate surface-
wave filters (SAW) are required. [1700], [1701] for video,
[1702] for audio. [1700] Is switched into the signal path for
DK/I-SECAM L/L' reception, if the signal SAWS is "high".
In this case the switches [7701], [7702] are open and the
diode [6700] is conducting. [1701] is switched into the
signal path for BG reception, if the signal SAWS is "low".
Then the switch [7708] is open and the diode [6701] is
conducting. For DK/I-SECAM L/L' reception, an additional
circuit for suppressing the adjacent channel audio carrier
is provided, which is set using coil [5702] to maximum
suppression at 40.4MHz.
2
PROM
IF Demodulator
TDA 9818
The IF signal from the tuner is processed by the
demodulator IC TDA 9818 [7703]. The signal PSS to pin3
switches between demodulation of positive SECAM and
negative PAL modulated video carriers. A QSS-audio-IF
signal SIF1 is generated for demodulation in the sound
processor [7600]. The audio-IF carrier is selected in the
audio SAW filter [1702]. This filter is switched for SECAM
L'. If the signal SB1 is "high", the switch [7707] is closed
and the diode [6702] is not conducting. For all other
standards the diode [6702] is conducting and the switch
[7707] is open. The output signal from this SAW filter is
first processed in the TDA 9818. Audio carriers are
converted from the tuner IF level into the audio IF position
and further processed in the audio demodulator [7600].
The AFC coil [5703] on the TDA 9818 is adjusted so that
when a frequency of 38.90 MHz is supplied to the IF output
of the tuner, the AFC voltage on pin 17 of the TDA 9818 is
2.5V. The setting of the picture carrier frequency for
SECAM L in the TDA 9818 is achieved by connecting pin 7
of the IC via a resistor [3702] to earth. The switch [7700]
and the signal SB1 "high" do this. The HF-AGC is set
using the AGC controller [3707] so that, with a sufficiently
large antenna input signal (74 dBV), the voltage at the IF
output of the tuner [1705] pin 11 is 500 mVpp. This setting
must be carried out, when the audio carrier is switched off.
The demodulated video signal appears on pin 16 [7703].
The demodulator AGC voltage at pin4 is used to
DRX-1
75
Advertisement
Table of Contents
