Retrace lines all over the screen _ High brightness _ Audio
OK _ Faint picture
FBT Number to this set is BSC24-01N 4013E
In most cases, there are two
reasons for this retrace lines. The
first one is with a high screen voltage.
In rare cases, the screen-pot meter [built inside the FBT] might be
faulty. If so, there is no repair to
this fault, other than replace the FBT/ [LOT].
The second possibility is reduced
video output stage supply voltage. This
voltage is generated by one among the winding of the FBT. For some sets, it will be from the main SMPS
section itself. This supply voltage may
vary from 280VDC to 290VDC. It will
depend upon the model & circuit of the TV. The most probable reason for a low video
output stage supply voltage is, either the diode that rectifies this voltage at
the FBT winding end is faulty; or the smoothing capacitor used with this DC
supply line has open. The capacitor
used here might be 10MFD to 22MFD; electrolytic type of high voltage rating. Usually it will be 10MFD350VDC.
If this capacitor is open, the DC
voltage will drop considerably, causing a very low voltage at the cathodes of
the CRT gun; which in turn make it high emitting (electron) state, causing a
screen of too high intensity along with vertical retrace lines. The lines will appear across the screen; all
over it, at a space of 1 or 2 inches.
They will be slightly slanted too; in position. I've attached the photograph of the effected TV
screen here.
What I did first is to check the
supply voltage to the video output section [CRT base card]. It was found normal here. And the fault
should be of an abnormal screen voltage.
When I noticed closely to the
screen, there is a very faint picture, but, it was or normal in size. Slightly expanded than normal.
The +B voltage from the SMPS
section should be suspected. I did check
it. According to the schematic, it
should be 108.5VDC at load.
But, here it shows about
117.7VDC. Much more than normal. Adjusted it.
There is a pot-meter on board at the SMPS stage circuit to this set. It can be adjusted. The SMPS of this set is an adjustable type,
not auto.
Ahh: It worked fine. No other adjustments have to do here. Cleaned the inside of the set and circuit
board using hot air blower. My work is over. Delivered after 2 hours check.
AFTER THE ADJUSTMENT
SCREEN POT-METER POSITION Here I haven't adjusted it any more
