Monday, November 10, 2014

AKIRA 21FBS1 - 21 Inch CRT TV - TROUBLESHOOTING


TROUBLESHOOTING & SMPS SCHEMATIC
NO PICTURE _ NO SOUND
  This failure is mainly caused by big-power circuit such as power supply, horizontal scanning, vertical scanning.
  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.
{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.}
ONLY ONE VERTICAL LINE AT THE CENTRE OF THE SCREEN
   This is a dangerous failure. It probable causes flash-over and smoking inside the set.  Don’ t let your TV work for a long time as this failure appears. Because the electron beam can not move in the horizontal orientation, the failure should be in the horizontal deflection circuit. We mainly check the open-circuit fault in horizontal deflection circuit.
UOC DOES NOT WORK
In television, remote-control system is similar with the computer system. In theory, it can work if it holds two conditions as follow:
# The power supply: In general, it is 5V, the error is not above 10% and the disturbance pulse is as small as possible.
##  The clock pulse: In TMPA88XX circuit, the clock pulse is generated by pin6 /pin7 of N204 and 8M crystal oscillator.  Television’ s remote-control system also needs reset circuit that can preset the values in internal register. The circuit around pin6 of N204 is called auto-reset circuit. If UOC detects errors in resetting, it will come to the state of program protected.
NO OSD
This failure is usually cause by the circuit of character generated and located. Most of reasons are that the horizontal and vertical fly back pulse signals do not come to UOC.
POWER SUPPLY REGULATOR [SMPS] SECTION CIRCUIT