HORIZONTAL LINE FAULT
Vertical linearity & Horizontal Line problems; CRT TVs
If you see a horizontal thin line
across the screen, with audio (sound) output is OK, make sure that the vertical
scan output circuit to the TV is faulty.
Do a visual check to all the solder terminals at the vertical scan output
IC, first. This IC will heat up to an
extent, when the set works. To radiate
heat out from it, the IC will be screwed on to a metal heat-sink, of Aluminum
or Copper. Make sure to tighten these seating screws, when you replace the IC. Check the screw up
condition. If the screw gets loose,
there will not be sufficient heat radiation from the IC to its heat-sink, and the IC
will overheat and finally it will fail to work.
As this IC will heat up to an
extent, during working, the solder terminals to it too will heat up. Repeated heating and cooling might make the
solder points to get loose contacted [electrically]; and these loose contacts might be microscopic to get detected
by naked eye. The best way is to
re-solder all the solder terminals of this IC, without making any solder bridge
short in between adjacent solder terminals.
In most cases, vertical line fault might be due to this type of solder
defect. If it does not help you; proceed
with further checking.
I hereby selected a vertical scan
output circuit to [JVC 21JT 5EU] as reference.
For most TVs, the vertical scan output might be similar, even if uses
other number Ices for this function.
Here TDA1771 is used as vertical scan output IC. Check all the components marked in squares
for failure. It will be best to check
all the resistors, after de-solder out its one end. It is recommended so; because, if you check
the value of resistors in circuit, there is a possibility to get wrong values
during measuring. All the components
that are venerable to fault are marked.
It will best to replace all the electrolytic capacitor used at the vertical scan output circuit at the same time. There will be 5 ~ 6 of it. It won't cost more. But, when replacing, make sure that the correct capacitance values are used, and be sure about the polarity (+ve & -ve) terminals of the electrolytic capacitor, when you insert it to the PWB.
TDA1771
When replacing [R301], make sure
that you are using the same Ohm value there; otherwise height & linearity
to the picture will be affected. Give a
special attention to [R303] (270Ohms 2W).
If this resistor opens, the vertical line fault will occur. It will be best to check all the related
components to this section; after de-solder out the vertical scan output IC from
circuit.
The capacitance value of C304 is
selectable. That is why; the capacitance
value is not marked there. Use a
capacitor of same capacitance value there.
Check the input voltage to IC
too. The two main voltages to check are;
voltage at its pin number (9-Vcc) & at pin number (2-Flyback generator).
Vcc voltage to this IC, is supplied from one of the winding of the fly-back transformer [LOT]; to most model & brand sets.
Just understand, troubleshooting is an art. Come to the exact fault point is the very important thing to any technical problems, whether it be in electronics, mechanical or any other field. An Ounce of Practical Experience is more than A a Ton of Theory; in the service and repair field. Patience and Concentration are the most important to a technician to proceed. I do say this, according to my experience since 42 years in the service and repair field, to all kind of electronic entertainment equipment.
Just understand, troubleshooting is an art. Come to the exact fault point is the very important thing to any technical problems, whether it be in electronics, mechanical or any other field. An Ounce of Practical Experience is more than A a Ton of Theory; in the service and repair field. Patience and Concentration are the most important to a technician to proceed. I do say this, according to my experience since 42 years in the service and repair field, to all kind of electronic entertainment equipment.
Some defects due to vertical scan output
VERTICAL SCAN OUTPUT SCHEMATIC [JVC 21" TV]
REMOTE CONTROL SCHEMATIC TO JVC 21" CTV
CLICK ON THE SCHEMATIC TO MAGNIFY (If needy)
