Circuit Descriptions, Abbreviation List, and IC Data Sheets
EN 183Q529.1E LA 9.
Over-current Detection
Over-current detection is done via components 3U05, 3U06,
3U15, 3U14, and 2U04 for the 3.3 V converter and 3U00, 3U01,
3U16, 3U17, and 2U00 for the 1.2 V converter.
Under-voltage Detection
There is an additional circuit (7U01-1, 7U01-2 and 6U04) to
switch “Off” the 3.3 V converter in case the +12VS drops below
9 V.
Service Tips
• When a power MOS-FET is found defective, replace the
other power MOS-FET as well.
• For a normal operation of the converter, it is important to
check the switching frequency and the value of the boost
voltage.
9.5 Front-End
Refer to figure “9-1 Architecture of TV522/92 platform” earlier
in this chapter for details. Refer also to block diagrams B02A,
B02B and B02C.
9.5.1 Device specifications
Tuner (TD1716)
The tuner has the following specifications:
• Hybrid tuner with symmetrical IF output.
• Down conversion from RF to IF frequency (picture carrier
39.875 MHz at analogue reception, centre frequency
36.166 MHz at digital reception).
• AGC control signal is coming from master IF device
(TDA9898).
• Only 5 V external supply needed (internal DC-DC
conversion to 3.3 V).
• 4 MHz output is used by channel decoder (TDA10048) and
master IF device (TDA9898).
The application in this chassis is as follows:
•I
2
C address C0.
• Broadband AGC, no IF section.
•I
2
C communication buffered via MUX.
• Gain to obtain optimised Master IF input level; AGC control
is completely inside the tuner.
• Output level ca. 110 dBμV (for strong input signal).
Repair tip: after replacement of the tuner, the option code
should be checked, even when the set appears to function
correctly! Refer also to chapter 5 “Service Modes, Error Codes,
and Fault Finding”.
Master IF (TDA9898)
• Down conversion from IF to low-IF frequency.
• Down conversion from IF to SIF.
• CVBS output.
The application in this chassis is as follows:
•I
2
C address 0x86.
• Down conversion from IF to low-IF frequency (5.166 MHz
centre frequency).
• Advanced filtering (for further rejection of adjacent
channels).
• Gain to obtain optimised channel decoder level. Control
signal is coming from channel decoder.
SAW filter
X6874D and X3451K
• Analogue sound for BG, I, DK, L, L’.
• DVB-T (digital reception sound and video).
For digital reception, the application in this chassis is as
follows:
• Rejection of adjacent channels.
• Switching is done by Master IF (3 inputs).
• One SAW covering both 7 and 8 MHz channels.
X6774D
• Analogue video for BG, I, DK, L, L’.
Channel decoder (TDA10048) DVB-T
The channel decoder has the following specifications:
•I
2
C address 0x10.
• Decoding from low-IF to MPEG transport stream.
• During decoding: de-modulation, de-interleaving and error
correction.
• External clock buffer required.
• No start-up requirements.
• AGC monitor.
Channel decoder (TDA10023) DVB-C
The channel decoder has the following specifications:
•I
2
C address 0x1C.
• Decoding from low-IF to MPEG transport stream.
• During decoding: de-modulation, de-interleaving and error
correction.
• External clock buffer required.
• No start-up requirements.
• AGC monitor.
9.5.2 Digital signal processing (front-end)
Refer to figure “9-5 DVB-C signal broadcast reception block
diagram” and “9-6 DVB-T signal broadcast reception block
diagram” for details of digital signal processing.
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