TV fault

HORIZONTAL THIN WHITE LINES ABOUT AN INCH SPACE ALL OVER THE SCREEN _ CRT BASED TVs

     This
is a common fault to occur in most of the CRT based televisions,
regardless of which brand it is. There will be sound OK, and a bright
screen with thin white horizontal lines across; at about an inch space
in between, all over the screen area. This fault may occur along with
color shades also, like blue screen with white retrace line, red screen
with white retrace lines, green screen with white retrace lines.

     Let us take
the first case. A white raster with white thin retrace lines across the
entire screen area. These are called vertical retrace lines technically.
To make it more understand, we have to go to some picture tube
electrode details.

     There are
three color cathodes for a color picture tube, Red, Blue and Green. Two
girds are there called Focus and Screen. Focus grid is supplied with
focus voltage which in turn determine the focus of picture, and screen
grid is supplied with screen voltage, will be much lower than the focus
voltage, which determine the emission of the picture tube. There is a
final anode supplied with Extra High Tension voltage, can be located at
the top side of the picture tube, to which the EHT [Extra High Tension]
voltage from LOT [Line Output Transformer] is connected with the help of
rubber cap and clip. Without these three voltages, EHT, Screen and
Focus, no raster will be produced. Therefore in our case, there is a
raster, so, horizontal output section including Line Output Transformer [LOT] is functioning well, and as far as sound is there, tuner and video
IF sections are working well. In fact, all other section except, video
output section is working properly.

There are three cathode points on the base card, marked as Bk, (blue
Cathode) Rk(Red Cathode) and Gk(Green Cathode). Check the voltages of
these three cathodes. In our case, it will be very low or approximately
equal to zero. When cathode voltages goes low, emission of the CRT
increases, is the reason. There must be a voltage between 120 and 135VDC
at these points. Find out the reason for this voltage drop is the next
step.

     The video
drive voltages in most TVs come from LOT windings, after rectification
and filtering. There will be one resistor of low value, say one Ohms or
so, will be connected series with this winding, in between rectifier
diode and winding. Check the voltage at the cathode of this rectifier
diode first. If found low replace the diode and the smoothing capacitor.
The smoothing capacitor will be between 33 and 47MFD 350VDC rating.
Replace both of them. If there is voltage, say 200VDC or so, check
whether this voltage comes to the CRT base board or not, If not, check
the conducting wire, serial resistors; if used for open. There is no
chance of transistor shortage at this time as the raster we see is
white. If raster we see have a specific color predominant, that is
green, blue or red, check the reverent video out transistors and replace
it. It is best to replace all the three video output transistors at the
same time with same batch and number

       Check the
soldering terminals of video output transistors’ load resistors (usually
have values from 12Koms to 15Kohms.  These resistors will heat up while
working.  Repeated heating and cooling may make the solder terminals of
these resistors to be loose, as a result, supply to the collector point
of respective transistor will go low.  In short, first look for any
loose soldering points on the picture tube base card [Video Output
Card].  In most cases, fault will be there.

SONY WEGA FLAT CRT TVs [SIX OR SEVEN BLINKS OF STANDBY LIGHT] (REPAIR HINTS)

      This TV has excellent quality
and no restrictions in viewing angles.  Other than its size and weight
it is much better than what is available with newer technologies at this
time.



     The most common fault to these
TVs are, blinking standby light.  Among them, most common are six of
seven time blinks, and either goes to standby, or OFF.  There is a
common solution for this problem too.  If IC 8002 or IC6501 on the D
board is found faulty in most cases.  Either only one among them might
be faulty, but it is a good practice to replace both of them at the same
time.  IC number is [MCZ 3001DB].  How to access this part.  you have
to open the back cover of the TV.  You must have knowledge in
electronics. 



     It is possible to remote the
entire back shell of the TV, by removing all of its screws, and sliding
it off.  There are a lot of screws, about a dozen of them which holds
the back cover in place.  Removing the back cover allows access D board.
 

Before removing the cover, just
unplug the TV from AC mains wall socket, and allow a few hours to the
high voltages to dissipate so as to avoid shock hazards.



     Some of the connectors are easy
to remove, but three high voltage wires connected to CRT is not easy to
unplug connections, and they should not be unplugged at all.  

There are a number of connectors,
need to be flip upwards, to disconnect the D board from an other
adjacent board.  If pull them upward, they will unsnap and pivot up 90
 degrees.  Unplug all the other cables and remove eight screws.  The
board will come out far enough to rotate it into position.  Such is the
mechanical fittings arranged by Sony, to do service work to this board.
 You must have a stubby screw driver to remove one screw that is far
forward and hidden between two connectors, and it comes just under the
picture tube.  Locate the ICs here on D board.  IC 8002&IC6501.
 Desolder them out from the circuit baord.  Use a desoldering pump to
suck out solder from solder terminals.



     Beware that each chip has two
pins are not soldered to board, and keep them like it is.  Take note of
the orientation of the chips.  There is a notch on one end facing the
closest edge of the board.  Never install the chip backwards.  If you
use sockets in case, you ever to do this repair again, since having to
unsolder these chips is most of the work.



     After replacing ICs with
sockets, install the replacement ICs.  Only one among these chips might
be bad, but it is best to replace both at the same time.  It might be
necessary to squeeze the pins together to get the legs aligned with the
holes in the socket.  This style of ICs has its leges spread out by
default, and so they might not automatically align unless you pre-bend
them inward a little to align the the holes in the socket.  Carefully
examine the chips after installation, make sure that the legs made it
into socket.  After re-installing the D board and attaching all the
cables, it would be a good practice to test it to make sure the repair
worked, before reinstalling the cover.