VESTEL 11AK20
Service Manual

7. POWER SUPPLY (SMPS) : The DC voltage sources required at various stages of the chassis are provided by an SMPS controlled by the IC801 (MC44603 for common models and MC44604 for �low power consumption on stand by mode� models). This IC is designed for driving, controlling and protecting the switching MOSFET transistor of SMPS (Q801). This supply has three outputs; one 112V output which is used for horizontal output and 33V generation needed by tuner section, one 16V output for all small signal sections an uC and one for audio output section. This chassis may be used in 90 - 270 volt with appropriate optional circuitry and components. The uC which is supplied by a source designed regulator with zener diode (D814) controls stand by mode by switching Q803 (for 44604 application Q806). 8. uC (MICROCONTROLLER) : The microcontroller hardware that is member of the ST6 family has a TV receiver control software with menu control. It controls the chassis through IIC bus, PWM outputs and I/O ports. Dominant features of controller are control of optional teletext, outputs for OSD, IR control signal receiving, and internal EEPROM. The controller has IIC communication port at # 40 , # 41 and OSD driver (R,G,B,FBl) at # 22, # 23, # 24, # 25. PWM control outputs are tuning # 34; vertical linearity adjustment # 1; AGC adjustment # 2. Other control outputs are Muting - video ident # 3; led driver # 4; system switches # 5, # 6, # 8, # 19, # 20, # 36; tuner switches # 18, # 19 and inputs are AFC information from IF # 9; keyboard # 10, # 11, # 13, # 14; scart mode ident (4/3-16-9) # 38, # 39; horizontal sync # 26; vertical # 27; infrared # 35 and reset # 33. The uC starts system according to option diodes configuration (D501, D503, D505, D506, D508). The controller has also a software which is able to control some service adjustments: R,G,B gain; R,G cut off; vertical position; vertical linearity; horizontal position; vertical amplitude; AGC; language selection for teletext. For enter to service mode followed procedure must be act within four seconds: 1Press volume down button on the keyboard; 2Press �prog� button on the R/C hand set; 3Press �- -� button on the R/C hand set; 4Press �TV �� button on the R/C hand set; Parameters can be sellected by program up and down, parameter adjustments can be done by volume up and down buttons. Memorizing the adjusted parameters can be done by pressing red button. For exit from service mode Press � TV �� button. 9. TELETEXT : The video signal coming from IF stage is fed to Data Slicer IC001. Then, there are two possibilities for decoding part; CF70095 or CF70195 for 1-Page simple text applications and CF7020X family for fastext and toptext applications. Finally, R, G, B and FBL signals are sent to the related inputs of STV2118. The alignment procedure for CF70095 or CF70195 application is as following: 1Apply a video with teletext transmission and select for teletext. 2Adjust the coil (VL001) for the voltage at pin # 28 2.5V. 10. CRT BASE-BOARD : When RGB signals enter the input of the video amplifier stage (CRT base-board), they are amplified by means of three symmetrical video amplifier stages. For this purpose three 2SC2482 high voltage, video output transistors are used. So, high gain-bandwidth product is achieved. Furthermore black level changes at the output amplifiers caused by temperature or component agings are compensated by means of a closed loop control system. For this reason the cathode current information (ICAT) is sent to STV2118.

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