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Model No: 21LAS1Bn
Version 2.0
2. B Two-None (no picture, no sound)
The failure shows that the set does not display the picture but it has noise wave or blue background
or OSD on the screen. This means that the circuits of power supply, horizontal scanning, vertical
scanning and video amplification are normal and they are not considered in the repairing. The
failures are mainly in the small signal processing circuits.
Before checking these circuits, a kind of practical test method is introduced. It is called “Signal-
input way ”. The detail is described as follow: We can use the resistance function of an analog
multimeter, connect the red pole (negative in ohm scope) on the circuit board ground, then touch
softly the test point with another pole (black pole) in ohm scope meanwhile observe the reactivity
on the output device.
Note : In the TV test, we mainly observe the noise wave on the CRT and listen to the noise voice
liking as “Ka…..Ka” from the loudspeakers.
a. No picture (see the diagram on next page).