電視干擾的檢查（Televisioninterferencecheck）

1、電視干擾的檢查(television interference check)the tv screen interference fault focus on exam in ation of parts and maintenanee techniques of 2008-11-09 18:02, a fault phenomenon and focus on examination of partsthe screen color tv produced by the machine interference fault occurs can be roughly divided into

2、 three categories: (1) high frequency interference: bright line, bright and bright interference: (2) if interference: all kinds of mesh, and scaly grainy interference; (3) low frequency interference: black, black, black interference the location and inspection object interference mainly includes:1.

3、switching power supply to focus on examination of the main power switch contact resistance is too large (normal ohm level); +300v power filter capacitor, switching transformer output voltage filter capacitor whether loss of contact resista nee of the contact; internal degaussing is close: a power sw

4、itch tube (or power thick film block) heat sink ground is good the parts often produce low frequency interference2. high frequency channel key substitution check check on agc tuner; whether the capacitanee loss or open circuit detection (such as the la768 foot external capacitor cl15); high frequenc

5、y bypass capacitor, snubber circuit has no open notch; image detection in the week, aft week is in phase shift; each contact is close: the shield ground is good. this part mainly produce high frequency interferencethe 3. line scan circuit mainly for oscillation circuit power supply voltage is insuff

6、icient; the line drive tube b value is lower (greater than 20), leading to lack of motivation. so as to form a vertical interference and promote the transformation of primary connected rc damping circuit elements whether open or metamorphic (value), line element output pipe, line output transformer

7、well, for example, the output transformer leakage inductanee will appear serious dark bars there are high pressure cap creepage sparking will produce interference spot high power component solder whether there are cracks, the output pipe heat sink ground is good, otherwise will produce black or blac

8、k interferencethe 4. output circuit mainly check the power supply voltage is too high; damping capacitance (such as field output block la7830, la7833 2, 5 foot between the capacitor, ta8403k, ta8427k, and the foot between the capacitor) whether the loss or open field; the output block heat sink grou

9、nd is good. the above bad scene thus the level of self-excited self high frequency interference or narrow leucorrhea black level low frequency interference, some models (such as changhong tv) with field output maintenance switch if the internal bad contact, there will be interference spot in additio

10、n, part of a field deflection coil connected in parallel with the damping resistanee, if the resistance is open then the screen will appear at the top level of fine white interference another output stage boost capacitor circuit or loss will make the upper grating multiple retrace line interference5

11、. video amplifier circuit of video amplifier circuit mainly 180廠200v as the discharge voltage is normal, whether the leakage diode rectifier, filter capacitor is loss or open. the fault phenomenon is usually reticulate and grainy or drawing like interference and low resolution image sanyo a3 machine

12、 as the discharge voltage from the power supply. when the 190v discharge voltage filter capacitor open will appear after the similar synchronization of an inclined screen without interference, the imageremove picture interference fault key two, troubleshooting method is to determine the scope of fau

13、lt as soon as possible, and then determine the fault point, comm only used methods are:the 1. observation observation method through fault screen and accumulate experience and a method of determining the scope of fault or the fault point for example, the screen appears black or black or black interf

14、erence, can determine the fault generally in the range of switching power supply or line and field scanning circuit, or if the vertical shape and real dark interference, can determine the fault line scanning circuit, the key is the output transformer bad2. if the short circuit method to determine th

15、e source of interference in the machine f note: whether the fault source can unplug the tuner signal plug in the machine, if the interference phenomenon remains unchanged, then the fault source in the machine, and outside of the machine), signal output can be used to the future will doubt the end ci

16、rcuit unit for short circuit, some disturbing phenomenon disappeared the fault source in short circuit or circuit before the unit itself for example, high-frequency d signal output terminal short circuit disappears after the fault phenomenon, it shows the fault point in high frequency tuner if the i

17、nterference is unchanged, can continue to short circuit in ic signal output terminal (if large signal processing ic short video signal output terminal). if the fault disappears, that the noise source in the channel or through the intermediate frequency interference in channel into the video channe1.

18、 if the fault is still in, then the fault may be depending on the channel or line and field scanning circuitthe 3. method is to use waveform waveform method of output waveform on suspected circuit of the oscilloscope examination, and compared with normal waveform, and a method to determine the fault

19、 point the normal output waveform of the method is to accumulate the circuit (waveform and some related parts of the tv on the drawing)4. substitution of suspect identification with replacement method can quickly find out the fault point, is a kind of method for easy detection of commonly used compo

20、nents, such as whether the self tuner, degaussing resistance is bad, the output transformer leakage inductance is serious etc this is the only way to optimize thethree examples of maintenance1 a hisense tc2111 tv image flashing, flashing a white line interference and sound mingled with the sound of

21、ka，but the image brightness the first suspected adverse short circuit if tuner tuner terminal image without but the white line is still short of interference, then small signal processing ic (la76804) 7 and 8 feet (if signal input), the interference phenomenon disappeared, the fault in the input cir

22、cuit suspected surface acoustic filter z101 (tsf1332l), itsreplacement test machine, troubleshooting. 2 cases a peacock kq54-39-5 tv appear poor image clarity and grainy interference,at the same time, brightness adjustment is invalid according to the experience of maintenance, failure is likely to p

23、ut in as. check three depending on the tube voltage c less than 100v, then check the discharge voltage filter capacitor c351 (4. 7 f / 250v) reduced capacity and leakage after replacement of the c351 fault disappears_3 a changhong c-2155 tv grating line width with brightness change and expansion. an

24、d the grating has a horizontal dark service moving downward. by the analysis of the phenomenon there may be too big and the internal resistance of the power supply with low frequency interferencethe effect of switch power source internal resistance is the main reason of excessive 4-300v and +b volta

25、ge filter capacitor. then check the +300v f 訂ter capacitor c507 (100 f / 400v), it was found that a capacitor leakage due to corrosion is broken, replace it after the test machine, the fault disappears.4 with a beijing: c2106 (sanyo a3) color tv, image clarity poor and severe level of white drawing

26、like interference and distortion phenomenon. due to high frequency interference, it is suspected, a high frequency amplification circuit in lnb self-excited, so the short circuit tuner intermediate frequency signal output terminal of if, found no image and sound. but the interference phenomenon disa

27、ppeared it is undoubtedly bad tuner change boot for genuine tuner, the fault disappears.5 a changhong ck51a (mil core) tv images with fuzzy interference spot fault, but the sound is norma1. because the sound is normal, it can troubleshoot tuner and channel, so the fault should be placed in the video

28、 channel after the the color / video processing block ic301 (an5612) signal input end of the foot on the ground short circuit, the interference spot fault disappears on the screen.the result shows that the fault point put in block ic101 (an5132) 12 (video signal output end) to the circuit between c3

29、01 feet, which is the maintenance switch s301. the switch has two groups a group to cut off or connect the video signal; another group used to short circuit or connect the field excitation signa1. when will the s301 dial to the service position. the screen can not become a bright line level, fault p

30、henomenon remains unchanged apparently s301 damage a new test machine, troubleshooting_6 a yingko cases of c51-3-rc tv image dim is not clear, like a ghost, and the occasional cross line interference from the failure phenomenon, there are problems like video channe 1. the video signal from the ic201

31、 (ta7698) 39 pin input is divided into two paths, one path within the inverted amplifier from the circle of 40 feet by 5 feet into the output, and by the circle of 37 foot color channels give synchronous separation circuit;another route circle 42 feet out put negative luminance signal, the chrominan

32、ce signal notch filter l601 chroma signal, get the luminance signal then the dl2 / luminance delay line after delay by c202 into ic201 feet (see photo), the internal black level clamp ring 23 feet from the amplified output when the short circuit ic201 3 feet, found interference lines disappear then

33、the foot short wire and open welding short circuit ring 42 feet, found to interfere with reproduction the result shows that the fault point between ic20 circle of 42 feet to the foot of the circuit disconnect the l601 pin, found the vanishing cross white line interference, obviously the fault point

34、is l601, and finally find out the l601 internal resonant capacitor for silver diffusion and leakage use a knife to scrape off the capacitor leakage bridge and black varnish treatment, recovery after the test machine, the troubleshooting. when the resonant capacitor leakage, a luminance signal is shu

35、nted to ground, so the image blur; because the chrominance signal string into the luminance channel and the formation of light interference_7 with a changhong d2525 tv, the screen, the upper level spacing of about 1cm fine black line interference and location is not fixed.that is the low frequency d

36、isturbance, first suspected of switching power supply. after careful examination of component solder and related filter capacitor the question was not found, then the external power supply test machine, the fault phenomenon disappeared. that point is still in the switching power supply according to the barrier finally, the replacement method to check out the degaussing resistance caused