VESTEL 15AK15
Service Manual

GENERAL BLOCK DIAGRAM OF CHASSIS AK19 .............................................................................................................................. 26 ELECTRONIC COMPONENT PART LIST ............................................................................................................................................... 27-28

DO NOT CHANGE ANY MODULE UNLESS THE SET IS SWITCH OFF The mains supply side of the switch mode power supply transformer is live. Use Mid Band E to PP 145.25 to 391.25 High Band QQ to 69 397.25 to 801.25

Noise is typically 6dB for all channels. Gain is minimum 38dB and maximum 50dB for all channels. Channel Coverage of UV1315: BAND OFF-AIR CHANNELS CHANNELS E2 to C E5 to E12 E21 to E69 FREQUENCY RANGE (MHz) 48.25 to 82.25 (1) 175.25 to 224.25 471.25 to 855.25 (2) CABLE CHANNELS CHANNELS S01 to S10 S11 to S39 S40 to S41 FREQUENCY RANGE (MHz) 69.25 to 168.25 231.25 to 447.25 455.25 to 463.25

Low Band Mid Band High Band

(1). Enough margin is available to tune down to 45.25 MHz. (2). Enough margin is available to tune up to 863.25 MHz. Noise Typ. Low band : 6dB Mid band : 6dB High band : 6dB Max. 9dB 10dB 11dB Gain All Channels Gain Taper (off-air channels) Min. 38dB Typ. 44dB Max. 50dB 8dB

4.VIDEO SWITCH TEA6415C In case of three or more external sources are used, the video switch IC TEA6415C is used. The main function of this device is to switch 8 video input sources on the 6 outputs. Each output can be switched on only one of each input. On each input an alignment of the lowest level of the signal is made (bottom of sync. top for CVBS or black level for RGB signals). Each nominal gain between any input and output is 6.5dB.For D2MAC or Chroma signal the alignment is switched off by forcing, with an external resistor bridge, 5VDC on the input. Each input can be used as a normal input or as a MAC or Chroma input (with external resistor bridge). All the switching possibilities are changed through the BUS. Driving 75ohm load needs an external resistor. It is possible to have the same input connected to several outputs. 5. AM DEMODULATOR TDA9830 The TDA9830 is designed for AM-sound demodulation used in L and L� standard. Sound IF Input: The sound IF amplifier consists of three AC-coupled differential amplifier stages each with approximately 20dB gain. At the output of each stage is a multiplier for gain controlling. The overall control range is approximately -6 to +60dB and the frequency response (-3dB) of the IF amplifier is approximately 6 to 70MHz. The steepness of gain control is approximately 10mV/dB. IF AGC: The automatic gain control voltage to maintain the AM demodulator output signal at a constant level is generated by a mean level detector.The AGC-detector charges and discharges the capacitor at pin 3 controlled by the output signal of the AM-demodulator compared to an internal reference voltage.The maximum charge/discharge current is approximately 5 mA. AM-demodulator The IF amplifier output signal is fed to a limiting amplifier (two stages) and to a multiplier circuit. However the limiter output signal (which is not any more AM modulated) is also fed to the multiplier, which provides AM demodulation (in phase demodulation). After lowpass filtering (fg @ 400kHz) for carrier rejection and buffering, the demodulator output signal is present at pin 6. Audio Switch This circuit is an operational amplifier with three input stages and internal feedback network determining gain (0dB) and frequency response (fg @ 700kHz). Two of the input stages are connected to pin 7 and pin 9, the third input stage to an internal reference voltage. Controlled by the switching pins 10 and 12, one of the three input stages can be activated and a choice made between two different AF signals or mute state. The selected signal is present at pin 8. The decoupling capacitors at the input pins are needed, because the internally generated bias voltage for the input stages must not be influenced by the application in order to avoid DC-plop in case of switching. Reference Circuit: This circuit is a band gap stabiliser in combination with a voltage regulation amplifier, which provides an internal reference voltage of about 3.6V nearly independent from supply voltage and temperature. This reference voltage is filtered by the capacitor at pin 4 in order to reduce noise. It is used as a reference to generate all important voltages and currents of the circuit. 4