ROADSTAR CTV-1415X
Service Manual

1.

11AK20 CHASSIS CIRCUIT DESCRIPTION GENERAL INFORMATION : This document provides detailed information about the fully I2C controlled Television Chassis named 11AK20.

11AK20 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 adjustments are made through I2C BUS control. This chassis has been designed mainly for the 90°, 14� and 15� 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 almost all the existing worldwide transmission and colour standards as PAL B/G/I/M/N, SECAM B/G/D/K/K�/L/L� and NTSC M (3.58), NTSC (4.43) using same Main Printed Circuit Board by means of optional components and settings. Tuning system is Voltage Synthesized for all systems Except NTSC M and PAL M/N applications but it is Frequency Synthesized for NTSC M and PAL M/N applications. Furthermore, chassis has also European Wide-range teletext solution as an option. This solution supports all the European teletext standards optionally as 1 page normal, fast and top text modes. The chassis has Euro AV Plug (Scart Socket) for Peritel and SVHS connections. The pictures in 16 - 9 format can be displayed via this Peritel 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 a menu driven user 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, Video and Audio from Scart or front AV RCA jack to be able to select the internal or external video and audio according to the control signals which comes from microcontroller and STV 2118. 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

2.1 Video and Sound IF System & Switch IC STV8223: STV 8223 is a picture and sound IF processor for negative application. The architecture of the video and sound demodulator, which are both based on PLL structure, allows a very good linearity of the Intermediate Frequency Response and an application with very few external components and adjustments. The volume on the audio signal is controlled through a DC level (pin # 13) which is provided from STV 2112/2116/2118 where all the I2C decoding is realized. STV 8223 also provides the audio and video switches for scart - AV applications. The IF inputs at pins # 19 and # 20 are driven by Tuner via Saw filter (Z101). The baseband signal produced from these IF inputs appears at pin # 3. This signal is used to produce sound trapped video signal and intercarrier sound signal. For multi-standard models, a switched trap circuitry is used (Q103, Q104, Q105). This internal video signal is fed to pin # 10 of this IC for internal-external (coming from scart) video switching and to the base of the buffer transistor Q102 for the video output of the scart connector. The intercarrier signal used for reproducing sound, passes through the band pass filter Z103 with center frequency 5.5MHz for B/G standard or Z104 for I (6.0MHz) or Z105 for D/K (6.5MHz) or Z106 for M/N (4.5MHz) in according to selected system by intercarrier signal switching circuitry (D106, D107, D108, D109, D110) and resultant signal is applied to the pin #8 of the IC which is the input of limiter and SIF PLL stage.
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