SONY TRINITRON KV1404 M3 SOUND OK NO PICTURE BRIGHT HORIZONTAL LINE ACROSS THE SCREEN
The fault is with its vertical sweep output section. 
It might be either vertical IC failure, or supply to vertical IC is absent.
To some sets, which have built in self diagnosis circuit, if the vertical IC fails to work, there will be no horizontal line. Because, when this fault occurs, the self diagnosis circuit at its main system control section will detect it, and will send a stop signal to the main power regulator section, and the regulator section will not supply any voltage to main board. On such sets, there will be "four" blinks of standby light displayed. at the front panel of the TV, indicates that the set do not get vertical sweep at all. Where the set has no self diagnosis circuit, a bright thin horizontal line across the screen will occur.
Caution: If this type of screen [with bright horizontal line across the screen] is noted, never use the Tv for more as it may burn the phosphor inside the picture tube, and a black line will be the result. This lind cannot be removed from the screen by no means. So if you not this fault, switch OFF the set, and call for repair. Never make any experiment with it, if you are not sound knowledge in electronics.
Here in this model set, an IC is used in vertical output section. [IC551 - UPC1488H]. This IC will heat up to an extent while it works. To prevent overheating, the IC will be screwed on to a large metal heat sink Look at the solder terminals to this IC, before you unsolder it, and make sure that it is faulty. Due to repeated heating and cooling, the solder terminals of this IC might get loose contacted. The first thing to do is to desolder out all the solder to its solder terminals, (7 of them), and resolder it with using good quality solder, and see whether it helps you. In most cases, this will be the fault. Unlike other fault, these loose solder terminals are very difficult to detect. They will be so samll to detect. That is why, I advice you to resolder them.
If this do not help you,
Check the supply voltage at pin number (3) of this IC. It should be around 15.4VDC. If you do not get this voltage, check the resistance between this terminal (3) to ground. If found less thatn 50 Ohms, the IC might be faulty. [internal short]. Cehck the voltage at the cathode of [D855 - RGP 10G]; connected to pin number (9) of line output transformer, via a [0.47] Oms resistor. Check this resistor for open. If found opened, suspect the IC. Check [C856 - 1000PF disc ceramic type] connected across the rectifier diode said above (RGP 10). If this capacitor have a sight leak, the vertical output IC won't get sufficient voltage to run, and will get defective.
It is a best practice to replace all the electrolytic capacitors to this section [4 or 6 of them], at the same time when you replace vertical output IC. Because all these capacitors will be at the vicinity of the vertical output IC, and will get heated along with this IC. During long term of run, there is a possibility to deteriate the value to these capacitors, which may turn more fault both in vertical linearity and with height of the picture.
