The main signal flow of the digital board is illustrated in the diagram below. The microprocessor HM602 controls the bus signals that are sent to several key components: the main board tuner (TDQ-6B7-FM3 or TM11-C232, which are not interchangeable), the sound processing block (NJW1168), HTV118, SAA7119 on the IPQ board, MST9886, and TDA9332. Among these ICs, except for TDA9332, the rest can have their bus pins disconnected to help identify non-power-on faults during testing. If the operating voltage of SAA7119 or HTV118 is abnormal, it will lead to a problem with the secondary bus voltage. When the power fails to turn on, the first thing to check is the 3.3V output from U200 (G960T63U) in the control system. If there's an issue with this IC or its surrounding components, the entire control system will fail to function.
Pin 25 of HM602 is the reset signal output, which should be around 3.25V under normal conditions. A low voltage at this pin can cause a bus error and prevent the unit from powering on. Additionally, the pulse waveform at pin 13 of TDA9332 (D608 positive) is a critical indicator of whether the line is functioning properly. If the voltage at this pin is normal (around 1.15V), any irregularity in the waveform can lead to boot failure or image centering issues.
Note: When the reset is working correctly, the positive terminal of D201 should read 0.7V. If this voltage is missing, the reset process won't complete, resulting in the device not turning on and the indicator light remaining off.
When HTV118 processes digital TV signals, it sends line and field synchronization signals to pins 12 and 11 of the HM602. These signals are then processed internally by the microprocessor to determine the scan format and frequency. This allows the digital conversion process to proceed normally. Any anomalies in the line or field sync signals directly impact the digital processing circuit, causing image distortion or unresponsive remote control functions.
U500 outputs the line F-IN and field reference VREF-IN signals from pins 69 and 90, respectively, and sends them to HTV118 pins 68 and 67. It also provides clock signals FIELD-IN and a 13.5MHz digital output from pins 87 and 48 to HTV118 pins 66 and 65. Abnormalities in these signals can result in no image or distorted video for TV, AV, and S-terminal inputs. The operating voltage and crystal oscillator circuit of U500 must be stable; otherwise, the display may show no image or color issues.
HTV118 receives eight digital video lines, along with field sync signals, line and field reference signals, and valid clock inputs. If the line or field sync signal channels fail, the received TV, AV, S, VGA, or HDTV signals will have no image. A no-grating fault is often caused by an abnormal voltage at the positive end of D606 and D607, which should be around 7.7V. Normally, D607 has a resistance of 13.9kΩ from the positive terminal to ground and 23.6kΩ from the negative terminal. To determine if the clock oscillation circuits of U500 and U301 are functioning, component replacement is a common troubleshooting method.
If U301 loses the line and field sync pulse input, but the working voltage of TDA9332 and the bus and oscillation circuits are normal, the line and field pulse forming circuit should still operate. If the device cannot receive VGA or HDTV signals, first verify the power supply to MST9886. Then, check the four-way line, field sync, and clock signal channels connected to MST9886. Under normal conditions, the voltages at R700 to R703 should measure 1.67V, 1.65V, 0.057V, and 0.035V, respectively. Any deviation from these values could result in the inability to receive VGA or HDTV signals.
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