Screen with Rainbow Colors [CRT based TVs]

Hello
This type of noise usually comes from a CRT based tv will be from its EHT cap. EHT cap is one which connected to the top of the p[icture tube, through which the extra high tesion voltage is supplied to it from the line output transformer. Normally there will be a smell of Ozone gas from the back side of the TV. Eht cap is a silicon rubber boot that protects the inner high tension voltage from being come to contact with open air. Due some reasons, if this rubber cap has some trouble; the extra high tension DC voltage supplied to the CRT [it usually come up to 32KVDC [32,000 VDC] will happen in contact with the open air, and if the humidity in air also is great, arcing will take place, converting Oxygen in the air to get converted to Ozone. If you look through the ventilation holes of the TV, in absolute darkness, you can see a bluish glow there aroung this anode cap. In some cases, this rubber cap can be replaced with a new one if available. if it is not available, you have to replace the line output transformer; otherwise called as [LOT]. This anode spot is a dagerous one for an unexperienced person to handle. because charged voltage will be there for a long time after switch OFF the TV.
It is best to contact an expereinced service person to get it repaired. OK.

Hello

There is no horizontal oscillation drive pulse reaching the horizontal output transistor. There are so many reasons for this fault. Line drive transformer's primary winidng open, its load resistor has opened, line driver transitor fault, absence of horizontal oscillating signal from the Ic , Line Output Tranformer otherwise known as [LOT] fault and so on.

If you have a digital multimeter, capable of measuring frequency, the thins will be easy. Take the frequncey at the base of horizontal output trnsistor, which in turn drives the LOT. It should be around 15625Hz or so, with no video signal. With a transmission signal it will synchronise to 15625hz; in PAL system. Anyway desolder the horizontal output transistor from board, and check it for collector to emitter leak, first. If it has leak, replace it with same type and number. If it is Ok, come towards the line drive trnsformer, a small transformer directly soldered onto circuit board, very near to the above said LOT. which in turn drives the horizontal output transitor.
One end of its primary winding will go to the collector of the horizontal drive transistor, which will be a small one, and the other end to the supply point through a resistor. Check the voltage of the resistor point of line driver transformer, and the check the voltage of the other end, which is connected to the collector of the line drive transistor. There must be wome voltage difference, between these two points, say at about 3 volts os so. If so, pto this point is ok, and line drive transistor is working, and it gets the above said frequency. If not suspect the Ic.
Upto this point is ok, and still there is no oscillation at the line outoput, means fault is in the above said LOT. Replace it with same type and number.
There is an easy way to check whether LOT is working or not. If LOT is working, there will be Extra High Tension voltage coming to the final anode of the picture tube. You just place your forearm parellel to the face of the picture tube, just a centmeter away from it, and switch on the tv with its mains switch. If LOT is working and EHT is there, the hair on your forearm should be attracted towards the picture tube and can make sure that LOT is working. If so fault is surely to mainjungle Ic, and it should be replaced. OK.

Gopakumar. India.