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The Roadstar 11AK36-Vestel is a 90° chassis television designed to operate with 14" picture tubes. It supports multiple television standards including PAL, SECAM, and NTSC, making it versatile for various broadcast regions. The sound system delivers a 3-watt RMS output into a 16-ohm load, providing clear audio. Additionally, the chassis includes one-page and US Closed Caption functionalities. For external connectivity, it is equipped with a 21-pin Eu-Scart connector.
The television's core functionality relies on the STV2248 video processor, which handles all small signal functions for color TV reception. This processor integrates a vision IF amplifier capable of demodulating signals with both positive and negative modulation. A key feature of the vision IF amplifier is its alignment-free PLL demodulator, which simplifies setup as the VCO (Toko-coil) frequency is factory-fixed. Different frequencies (38.9 or 45.75 MHz) can be selected by changing the coil itself.
For sound processing, the chassis utilizes a QSS (Quasi Split Sound) sound circuit in some versions. This circuit includes a sound IF amplifier with an external AGC de-coupling capacitor. A single reference QSS mixer converts the SIF signal to the inter-carrier frequency by mixing it with a regenerated picture carrier from the VCO. The mixer output is then filtered by a high-pass filter to attenuate residual video signals, enabling high-performance hi-fi stereo sound. AM sound demodulation is achieved by multiplying the modulated sound IF signal in phase with the limited SIF signal, with the output filtered by a low-pass filter to attenuate carrier harmonics. The AM signal is then routed through a volume control.
In mono versions, an FM demodulator is implemented as a narrow-band PLL with an external loop filter, providing necessary selectivity without an external band-pass filter. This design ensures good selectivity through a linear phase detector and constant input signal amplitude. The nominal frequency of the demodulator (4.5/5.5/6.0/6.5 MHz) is tuned via a calibration circuit using the clock frequency of the micro-controller/Teletext decoder as a reference. Software controls the frequency setting and monitors PLL lock status, enabling an automatic search system for incoming sound frequencies. De-emphasis output signal amplitude is independent of the TV standard, and the audio control circuit includes an audio switch and volume control. The Automatic Volume Leveling (AVL) function can be activated in mono inter-carrier sound versions, stabilizing the audio output signal.
Video switching is managed by the STV2248C video processor, which features three CVBS inputs and two RGB inputs. One CVBS input is for external SCART 1, another for FAV, and the third for internal video. Software switches control the selection between external video inputs.
The synchronization circuit, also part of the STV224X video processor, handles horizontal and vertical processing. It controls the external horizontal deflection circuit via the Horizontal output pulse (HOUT) and performs vertical scanning through an external ramp generator and a vertical power amplifier IC controlled by the Vertical output pulse (VOUT). Key components of the deflection circuit include PLL1 (a phase-locked loop for locking the internal line frequency reference on the CVBS input signal), PLL2 (for controlling horizontal output phase and position adjustment), a vertical pulse extractor, a vertical countdown system for generating vertical windows, automatic 50/60Hz scanning identification, PLL1 time constant control, noise detector, video identification circuits, horizontal coincidence detector, and a vertical output stage with de-interlace, vertical position control, and vertical amplitude control.
Chroma and luminance processing are also integrated into the video processor. The chroma decoder supports PAL, NTSC, and SECAM signals. PAL and NTSC sub-carrier demodulation uses a synchronous demodulator and an Xtal PLL locked on the phase reference signal. SECAM demodulation uses a PLL with automatic calibration. Color standard identification is based on burst recognition, with automatic and forced modes selectable via the I2C bus. NTSC tint and auto flesh are I2C bus controlled. The Xtal PLL can handle up to three crystals for PAL M, PAL N, and NTSC M. ACC (Automatic Color Control) manages chroma sub-carrier amplitude within a 26dB range. All chroma filters are integrated and tuned via a PLL locked on the Xtal VCO signal. A second PLL fine-tunes the SECAM bell filter during frame blanking. A base-band chroma delay-line rebuilds missing color lines in SECAM and corrects transmission phase errors in PAL. The luminance processor includes a chroma trap filter, a luminance delay line, a peaking function with noise coring, and a black stretch circuit.
The RGB output circuit processes R, G, B signals from three sources: YUV inputs (from the luma part and chroma decoder), external RGB inputs from SCART (converted internally to YUV or direct YUV from a DVD player), and internal RGB inputs (for OSD and Teletext display). Main functions include YUV inputs with integrated clamp loop, external RGB inputs (RGB to YUV conversion), YUV switches, contrast, saturation, brightness controls, YUV to RGB matrix, OSD RGB input stages, 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 I2C adjustments, half tone, oversize blanking, external insertion detection, blue screen, blanking control, and RGB output stages.
The ST92195 micro-controller, a member of the ST9+ family, manages the TV receiver's operations. It includes a Central Processing Unit (CPU), ALU, Register File, and interrupt controller. Peripherals include voltage synthesis, VPS/WSS slicer, Teletext slicer, Teletext display RAM, OSD, a watchdog timer, a serial peripheral interface (SPI), a 16-bit timer, and an A/D converter. It displays program number, channel number, TV standard, analogue values, sleep timer, parental control, and mute via OSD. A single LED indicates standby and on mode. System configuration is done through a service mode, and it provides 3-level logic output for SECAM and tuner band switching.
The chassis supports various tuners, including PLL or VST types. UV1316 (VHF/UHF) is a PLL tuner, UV1336 is a PLL tuner for PALM/N, NTSC M applications, and UV1315 (VHF/UHF) is a VST tuner. These tuners cover different frequency ranges for off-air and cable channels, with typical noise levels and gain characteristics.
The sound output stage uses a TDA2822 AF output amplifier, supplied by +12VDC from the SMPS transformer. The vertical output stage uses a TDA8174A power amplifier, suitable for 90° and 110° color deflection systems across various field frequencies and picture tube aspect ratios.
The power supply (SMPS) uses an UC3842/3 IC to control the switching transistor, providing 115V for FBT input, ±12V for audio output, +5V, and 8V for the ST92195. Discrete video amplifiers use three high-voltage, high-frequency transistors for RGB amplification, operating on fixed AC and DC gains.
The 24C08 is an 8Kbit EEPROM for serial access, organized as four blocks of 256x8 bits, compatible with the I²C standard. It operates with a power supply as low as 2.5V and offers features like 1 million ERASE/WRITE cycles, data retention for over 10 years, byte and multi-byte write, page write, and byte, random, and sequential read modes.
For maintenance, the service manual outlines safety precautions, including switching off the set, using an isolating transformer, and ensuring service is performed by qualified personnel. Critical components marked with a warning symbol must be replaced with identical parts. Power and fused resistors must be mounted as per the original component. EHT should not exceed 26kV. When the TV is switched off, a short-circuit between the HV-CRT clip and CRT ground layer is recommended, and C808 should be shorted before changing IC841 or other primary SMPS components. Measurements are taken under specific conditions: 60dB antenna signal level, color bar pattern (100% white, 75% color saturation), normal picture performance brightness, contrast, and color, and 220VAC, 50Hz mains supply.
The service menu is accessed by entering the main menu and then pressing 4, 7, 2, and 5. Parameters are selected using the up/down buttons and adjusted using the left/right buttons. Color buttons on the remote control have specific functions in service mode: RED switches AVL ON/OFF, GREEN switches PICTURE MODE between 4:3 and 16:9, YELLOW switches to VERTICAL SCAN DISABLE mode for screen voltage adjustment, and BLUE adjusts AGC and IF automatically.
White balance adjustment involves using a Color Analyzer and adjusting WR (RED), WG (GREEN), and WB (BLUE) parameters. AGC adjustment requires a 60dBmV RF signal (channel C-12, 224.25 MHz), selecting the AGC parameter in the service menu, and pressing the BLUE (INSTALL) button for automatic adjustment. IF negative adjustment (without L' systems) involves a PAL color bar pattern at 38.9 MHz, applying it to tuner PIN-10 and PIN-11, pressing PROG-1, then BLUE (INSTALL), selecting BG or I standard, and adjusting IF1. IF positive adjustment (with L' systems) uses a SECAM-L color bar pattern at 33.9 MHz, applying it to tuner PIN-10 and PIN-11, pressing PROG-1, then BLUE (INSTALL), selecting BAND VHF-1 and L' standard, and adjusting IF1. OSD horizontal position is adjusted by selecting the OSD parameter and using the reference bar. Teletext brightness is adjusted by setting the TV to a Teletext channel, entering the service menu, pressing TEXT, and adjusting the BRIGHTNESS parameter to 30.
General| Display Technology | CRT |
|---|---|
| Chassis | Vestel |
| Brand | Roadstar |
| Model | 11AK36-Vestel |
| TV Type | Standard |
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