Fault phenomenon: After turning on the machine, there is no response inside. Analysis and maintenance: After turning on the machine, if there is no response inside, the fault mostly occurs in the switch power supply or the line scanning circuit. First, check the power fuse F601, it was found that F601 has turned black. The blackening of F601 indicates that an overcurrent phenomenon has occurred. Use a multimeter R 1Ω range to measure the resistance between the terminals of the filter capacitor C604 in-circuit, and the result is close to 0Ω. The main cause of this phenomenon is either the breakdown short circuit of C604 or the breakdown of the power switch transistor. Observing the exterior of C604 shows no discoloration or other adverse phenomena. Then, use the multimeter R 1Ω range to measure the resistance between pins ①, ②, and ③ of the thick-film block IC601 in-circuit, and the results are all close to 0Ω, indicating that the internal power switch transistor Q1 of IC601 has broken down. Checking the negative feedback resistor R609 connected to the emitter of Q1 reveals it to be normal.
The switch transistor is often damaged due to excessively high reverse peak voltage, excessive load current, as well as high turn-on or turn-off losses. Using a multimeter R 1Ω range to measure the +B overvoltage protection diode D609 in-circuit shows it to be normal, checking the spike absorption circuit capacitor C605 also reveals it to be normal, thus excluding the possibility of damage caused by overvoltage. Checking the constant current drive circuit's diode D602, capacitor C629, and resistors R623 and R604 all show them to be normal, thus excluding the possibility of high turn-on losses. Considering that the machine may have been damaged due to prolonged operation time and excessively high ambient temperature causing the switch transistor to overheat and break down, or due to large turn-off losses damaging the switch transistor before the voltage stabilizing circuit and the constant current drive circuit for the switch transistor start working at the moment of turning on the machine.
Replace the faulty thick-film block with a genuine STR-S6307, replace F601 with a 2A regular fuse, unplug the connection plug between the demagnetization coil and the motherboard, Beijing Sony TV repair phone number, and disconnect one lead of R620. After powering on and testing, everything works normally. After disconnecting the power, reconnect the demagnetization coil plug, resolder R620, and replace the 2A fuse with a 3.1A delay fuse. Testing after these steps shows everything works normally.
Sony KV-R21 TV, after turning on, there is no response inside.
Source of information: Beijing Sony TV Repair Phone Number http://blog.tianya.cn/blogger/blog_main.asp?BlogID=3682079.