Today, I repaired a Xiahua 34-inch model. The specific model was not seen. The chipset is 87CK38N+TB1238. The main board is divided into two parts, one is the small signal part, the other is the high-power circuit [power and field scanning], the outer casing is not on, the power board has been removed and set aside. It has been put on hold for about a year. This machine has been repaired by others. The power supply has been replaced with a universal module. Some components do not know where to go. I don’t know the parameters. Because it is home repair, the original circuit cannot be restored. Arts And Crafts Casting,Hpdc Die Casting,Aluminum Die Casting Air,Die Casting Aluminium Alloys Dongguan Metalwork Technology Co., LTD. , https://www.diecast-pro.com
Try to power on, did not find abnormal [not connected to the signal circuit] after all the circuits are connected, boot high voltage ignition, and quickly shut down! After processing, the screen turns on. The measured main voltage is only about 90 volts, the screen is not full, and there is a big screaming sound. Try to adjust the module potentiometer, the highest is about 90 volts. It is suspected that the module is bad, change again. One module, no improvement. How to do? The circuit can work, and it proves that there is no serious short circuit. The voltage can be adjusted to 150 volts and stable at no load. It proves that the module is basically intact. In the uncontrollable way, I suddenly think that the module and the switch transformer do not match? Installation instructions read [I generally do not read], remove the switch transformer, according to the instructions, the primary winding of the switching transformer from the original two-wire parallel to single-line series, [specific method, please refer to the manual, I will not Said], on the machine, the module output is adjusted to the minimum [avoid the output voltage is too high] measured voltage 90V, slowly adjust, the voltage slowly rises, the upper body to 110 volts, and then through the analysis of the circuit found The sampling circuit has a SE115, and the initial voltage is initially determined to be about 115 volts. After the voltage is adjusted to 115 volts, the screen is just full, but the power supply still has a large howling sound. If the inspection circuit does not find an abnormality, what should I do? After calming down, carefully observe that although the screen is normal, I found that there is a S-shaped twist that is extremely difficult to find, and the truth is white! It turned out to be a problem with the filter capacitor! At this point, I noticed that the 300 volt filter capacitor was replaced. It seems that the time is not long. It is the kind of brown small 220UF capacitor that is common in the electronics market. Decisively removed, found that the fruit is really lost, replaced with a high-quality disassemble filter capacitor, whistling disappeared, S-shaped twisting is gone, after a period of downtime, confirm OK after the end of maintenance: The machine repair time was more than an hour. Later, it was proved that the module was completely normal. It changed the switch transformer and replaced a filter capacitor. Charge, you know........