CIRCUIT DESCRIPTION OF THE 11AK20S CHASSIS
1. GENERAL INFORMATION :
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This document provides detailed information about the fully IC controlled Television Chassis named 11AK20S.
11AK20S is based on the bus controlled circuits in which all the filters, traps and delay lines have been
integrated. Therefore the numbers of external components are reduced and the user, service and factory
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adjustments are made through IC BUS control.
This chassis has been designed mainly for the 90°, 14? picture tubes.
This chassis has a SMPS circuitry, which has been designed to get low stand-by power consumption (less
than 3W) as an option. On the other hand, it also has wide range (90-270V 50/60 Hz) mains as an option.
The chassis covers many transmission and colour standards such as PAL B/G/I, SECAM B/G/D/K/L/L? and
play-back NTSC M (3.58), play-back NTSC (4.43) using same Main Printed Circuit Board by means of
optional components and settings. Tuning system is Voltage Synthesized for all systems.
Furthermore, chassis has also European Wide-range teletext solution as an option. This solution supports all
the European teletext standards as 1-page normal text modes.
The chassis has an Euro AV Plug (Scart Socket). The pictures in 4:3 and 16:9 format can be displayed via
this connection. Other optional external connections are front AV input RCA jacks, back AV output RCA jacks
and Headphone jack.
The software has been developed with an user-friendly menu driven interface supporting all possible chassis
versions with a storage capacity of 100 programs.
2. IF STAGE :
The inputs for IF stage are IF inputs from Tuner to produce front-end Video and Audio,the external inputs are
Video and Audio from the Scart or from the front AV RCA jack to be able to select the internal or external
video and audio according to the control signals which orginates from microcontroller and
STV2118.(Furthermore. the RGB inputs which are direct inputs to the STV2118 via the scart can also be
selected by the software).Then, the resultant video and audio signals are sent to video processing stage and
audio output stage, respectively. Furthermore, front-end video and audio signals are sent to scart and or back
AV RCA jacks. This part also produces some control signals for tuner and microcontroller.
This stage was designed for processing positive (optional) and negative modulated mono and one scart
applications.
STV 8223 is the IF IC that is used in only negative modulation. There is an alignment which is the VCO
adjustment (VL101). The procedure of alignment can be described briefly as follows :
?The IF signal is applied to the IF inputs in accordance with the standards (for B/G 38.9MHz)
at pin #1 and 2 of SAW filter (Z101).
?Adjust the VL101 until getting 2.5 V at pin #9 of uC (IC501).
dc
This stage is also used for negative and positive modulated, mono applications. STV 8224 (negative and
positive modulation and FM sound) (IC 101) and STV 8225 (AM sound) (IC102) are the IF IC?s.
There are two alignments in this case, which are the VCO adjustment (VL101) for B/G - L standards and
VC101 for L? standard. The procedure of the alignments can be described briefly as follows :
?The system is Switched to B/G standard reception,
?The IF signal is applied to the IF inputs in accordance with the standards (for B/G 38.9MHz)
at pin #1 and 2 of SAW Filter Z101.
?Adjust the VL101 until getting 2.5 V at pin #9 of uC.
dc
?The system is Switched to L? standard reception,
?The IF signal is applied to the IF inputs in accordance with the standards (for L? 33.9MHz)
at pin #1 and 2 of SAW Filter Z101.
?Adjust the VC101 until getting 2.5 V at pin #9 of uC.
dc
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ACEC
