Konka ST system HD CRT TV repair three cases of the countryside

Example 1: Konka P29ST390-TV, three no.

analysis of repair: power test machine and AD1895AYRSZ datasheet and found that the power indicator light, press the panel buttons and AD1895AYRSZ price and remote control and AD1895AYRSZ suppliers and can not turn the standby button, open the back cover, measuring standby control tube V960 (2SC1815) is extremely high potential base , indicating that the tube is saturated conduction state, the measured CPU (U23, M3n622SPGP) (11) feet (external crystal) voltage is also normal; measured CPU power supply terminal ((14), (16) feet) voltages are normal, Replacement crystal Y4 (10MHz) after the test machine fault persists.

based on past experience, CPU, video digital processor SVP-EX11 often due to pin Weld, short circuit fault caused by a black screen and no map. Double-check the pin, and did not find Weld, short circuit and so on.

re-welding of the pin after the test machine, the fault still; final resistance measurement with related test points one by one measurement, when measured to the exclusion RN3, and found pin-to-ground resistance value is too large, then measure the pin voltage power only 3.8V (normal is about 4.8V), remove the measure, but it is normal, and then measuring its former level, the electronic switch U22 (49F9T5K) (13 ) pin voltage is low. Shown in Figure 1, CPU (42) feet RD output control signals, processed by U22 from it (13) feet send, sent to the video digital controller U1 (SVP-EX11) of (170) feet, to control the chip read and write inside the video information.

measurements that, CPU (42) feet RD signal output voltage is normal, it is believed U22 internal circuit problem, its renewal after the test machine, map the sound back to normal, and then measured RN3 feet voltage returned to normal.

Example 2: Konka P34ST386-TV, the line width is narrow.

Analysis of maintenance: After boot, found images, sound are normal, and only the line width dissatisfaction. First, enter the debug menu to adjust the factory line rate parameters. Into the data bus as follows:

press the menu button on the remote control to display the Debug menu, the menu does not disappear even before the press "look back" key five times, you can debug into the factory menu page. Modify "HSIZE" (line width) values, have found that the rate did not change. Exits, openings check the line capacitance C402 ~ C404 reverse process is good, then check the line output circuit also found no abnormalities.

got drawings analysis, causing the line or the reasons for dissatisfaction rate line scan circuit. Aircraft field scanning signal from the digital board of the U31 (TB1306FG) production, shown in Figure 2. The pin voltage is measured and found the line blanking pulse (FBT) input pin feet) voltage does not, check its related components R417, R418, It491, D58, found resistance R491 (470) has increased to 500k. R491 resistance increases, leading to the line flyback pulse signal amplitude decreases, and thus appear dissatisfied with the line width phenomenon. Renewal after the test machine, troubleshooting.

Example 3: Konka P29ST390 TV, turn off automatically after about 10s.

Analysis of maintenance: pick up after the power test machine and found the screen bright after the shutdown, the moment after turning on to hear audio. The first suspect protection circuit in question, after careful examination, and found no abnormalities. Detected with the dummy load switching power supply, and the brightest output voltage is normal. Check field scanning processing circuit, measuring U31 (TB1306FG) of the pin voltage, the voltage is only found foot 0.25V, while the normal should be as 3.3V. See Figure 2, the pin voltage is rectified by the switching power supply VD954, C964 filtering, N952 (7809) three-terminal voltage regulator output 9V, then by the foot strip XS01 digital board connected to the circuit, the inductance FB50, resistor R492, zener D57 (3.3V) input to the U31s foot .

follow it all the way, it was discovered regulator D57 (3.3V) a pin Weld, re-patching and, U31 pin voltage is back to normal, the test machine troubleshooting.