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File name LG MC-64A Sch. and Adjusments.pdf

ADJUSTMENT INSTRUCTIONS * Safety precautions 1. It is safe to adjust after using insulating transformer between the power supply line and chassis input to prevent the risk of electric shock and protect the instrument. 2. Never disconnect leads while the TV receiver is on. 3. Don't short any portion of circuits while power is on. 4. The adjustment must be done by the correct appliances. But this is changeable in view of productivity. 5. Unless otherwise noted, set the line voltage to 220Vac+_ 20%, 50/60Hz. * VCO (Voltage Controlled Oscillator) Adjustment Test Point Adjust JP4(L504) : VL501 : 1) Turn on DC power supplies. 2) Adjust VCO ADJ. coil(L501) so that the level of Picture Carrier (PC) may be at the lowest position as shown Fig. 2. *T est Equipment required 1. 2. 3. 4. 5. 6. 7. Swee p Generator Marker Generator(38.0MHz: Picture/32.5MHz: Sound) Alignmen t Scope(5121A) Patter n Generator(PAL/SECAM) DC Power Supply Color analyzer Multimeter(Volt meter) SC (Sound Carrier) : 32.5 MHz PC (Picture Carrier) : 38.0 MHz Fig. 2: Output waveform on Alignment Scope Preparation for VCO Adjustment 1. Connect the measuring equipment to the TV as shown in Fig. 1 2. Set RF output level of Sweep Generator to 90dBuV. NOTE : When performing this adjustment, if there are 2 adjusted point in VL501, select the lower core position. * RF AGC (Auto Gain Control) MAIN BOARD C533 (JP 3) Z101 (JP 1) 5 7 CK 0.01uF 3.3K L504 (JP 4) 1 TUNER IC401 Adjustment Test Point :J9(AGC ADJ.) or Observing Display :VR501 48 IC501 Adjust J9 AGC ADJ. VL501 VCO ADJ. (JP 6) The RF AGC control VR501 was aligned at the time of manufacture for optimum performance over a wide range conditions. Readjust VR501 should not be necessary unless unusual local conditions exist, such as; 1) Channel interference in a CATV system 2) Picture bending and/or color beats, which are unusually due to excessive RF signal input when the reciever is too close to a transmitting tower or when the receiver is connected to an antenna distribution system where the RF signal has been amplified. In this case, the input signal should be attenuated(with pad or filter) to a satisfactory level. 3) Picture noise caused by "broadcast noise" or weak signal. If the broadcast is "clean" and the RF signal is at least 1mV (60dBu), the picture will be noise free in any area. RF out Hor SWEEP S.G with Marker Alignment Scope Ver DC POWER SUPPLY 5.0 + 0.1V DC POWER SUPPLY 16 + 0.5V Fig. 1: Connection Diagram of Equipment for VCO Adjustment - 1 - Adjusting the VR501(RF AGC) control to one end of rotation will usually cause a relatively poor signal to noise ratio; Adjusting to the other end of rotation will usually cause a degradation of over load capabilities resulting on color beats or adjacent channel interference. For the best results, adjust VR501 contol while performing on all other local channels, or Refer to the following Table 1. Tuner P/N 113-118C/D/F 113-238H Maker Adjustment Voltage REMARK RF 60+_1dBuV