Probe current voltage pin 420*4450 head diameter 5.0 over current current and voltage pin

DFN1006 TP-RCLAMP3321P ESD Diode Low Capacitance

Skyworth LCD TV 32E55HM (8R28 movement) speaker noise large maintenance boot image with sound normal, a while in the speaker with a rustling sound, playing for about 3 minutes, the noise is basically submerged with sound. Test machine, use the network set-top box HD interface to connect to the TV HD interface, the same as AV1, AV2 phenomenon, reduce the TV volume, the accompanying sound can be reduced, but the noise volume does not change, when the TV volume is adjusted to 0, the noise disappears .
Start up, measure the output of the power board, 5v, 12, 24, normal, in the sound supply 24v end to the ground and 1000u capacitor, invalid, at this point, basically eliminate the power board failure.
Visually check the motherboard, the main chip has a heat sink attached, the model does not know, considering that the machine can hear the sound when it is just turned on, and the longer the sound, the smaller the sound, it seems to be related to temperature, using alcohol cotton ball plus hair dryer cold air cooling motherboard The chip, when cooling the main chip phenomenon has improved, but can not completely eliminate the noise.
Look at the motherboard has four three-terminal regulator, U14=5.07U13=2.64U10=1.26U12=1.33
Because there is no data, based on experience, I feel that u10 is basically normal for the core voltage of the chip. Maybe u12 should be 1.8v branch. Measure the input of U12 by 3.3v, (3.3-0.7-0.7=1.9), then take two common diodes in series. Use one hand positive pole to connect U12 input, negative pole to connect output (playing state), the sound is clear, the measuring voltage is 1.41v, but the diode is hot, so it is turned off, and the four diodes are connected in parallel and then connected in series to the input and output of u12. The terminal is used to increase the current, and the TV does not start up (the red light does not turn to the green light). The u12 output is measured to be 1.67, and the diode negative electrode is soldered. The boot state is connected and normal again. It seems that this is not handled properly.
Look carefully at the board and find that u12 is an adjustable three-terminal, R187 (330 ohm) is connected to u12 output and control pin (I call it the upper adjustment resistor), R186 (model is not clear), respectively, connected to the control foot and ground (lower) Adjust), then take 330 ordinary resistance in parallel on R187, of course, the welding point is selected in the output and control legs of U12. Boot, normal sound, measuring U12 output is 1.44V, has been tested for 5 hours. The sound is clear and loud. I don't have any information. I don't know what the specific output of U12 should be, but I can be sure that it is lower than 1.33 and higher than 1.67. This inspection is a fuzzy overhaul. If it is wrong, please master the axe. At the same time, this confirms a sentence, troubleshooting power supply

Look at the R186 mark 220 with a magnifying glass, which should be 22 ohms. Using the welding torch to blow r186 measured to 22 ohms, r187 is 330 ohms are normal, with a 20 ohm and 10 ohm resistor series replacement r186, the measured U12 output is 1.35v, the test machine is all normal. At this point, this machine is fixed.