A panasonic TC - 2188 color TV sets in the condition of TV, grating has a faint line of out-of-step phenomenon; Sound is normal. Pull the antenna, the grating of light snow; Conversion AV state, images, sounds, all normal.
 
According to the maintenance experience, can preliminary judgment TV video signal output circuit fault, but there were no suspicious components, check the relevant circuit when forming troubleshooting.
 
Then according to the fault phenomenon further analysis:
 
AV image. Main circuit is normal, TV audio and high frequency circuit is normal, should check the AV video conversion circuit mainly at this moment, as shown in the appended drawings.
 
 
Through inspection, in the state of AV, A point in the appended drawings clear signal waveform is normal. But in the state of TV, point A synchronous signal waveform of short head (little) : basic view point B wave normal again.
 
Will C206 welding inspection under normal: then 0258 welding inspection, found that c, e, between the multimeter black pens and meet extremely, red pens and e, c 250 k Ω leakage resistance, and with red pens and c extremely extremely, black pens and e whose hands micro: when measured with a multimeter R * lk block b, c between a and b and e very basic normal to the resistance between the positive and negative. Thus illustrate Q258 bad, the c and e interpolar leakage resistance attenuation the synchronization signal, which in this case of failure. After Q258 change new. Failure completely ruled out.
 
Summary: in the appended drawings, when 0258 c and e interelectrode appeared positive leakage resistance, as between c and e pole and a negative ground diode fuses iconic in the presence of synchronization head signal conduction state, will head the signal attenuation or bypass. At this time only use voltage, resistance test is difficult to judge fault reason, and when using waveform observation method, the be clear at a glance. In some difficulty in troubleshooting, therefore, learn to use the oscilloscope, it is very important.