Monday, August 21, 2017

Solving CRT television picture colour problems- Picture is purple, Yellow, light blue.

The colours you seen on your TV screen is a products of the three primary colours (RED, GREEN and BLUE).
So if one of the primary colour is missing then the picture will be affected.

What you are seeing above there on that screen is a classic example of one of the RGB colours missing.

For simplicity I have reproduced the effect of one colour failure on the above chart.

When the red colour is missing then what is remain is the product of GREEN and BLUE which is Light blue as you can see on the chart.

With that little introduction let as use the above chart to figure out the missing colour on the TV screen presented above.

The picture is purple right? Then go to the chart and look at the second column (screen colour) =purple. Then check the missing colour which in our case is GREEN.

So we can conclude that the green cathode has a problem and therefore you should go to the small CRT neck board and look out for the G cathode and test all the components on that line only.

Start with the obvious, dry joints, the actual transistor (Green) amplifier could be faulty or there is no Green signal at the base of this transistor.

Again you can use the method i introduced to you of voltage testing on the RGB circuit and writing them down and whichever voltage is very different from the other is the culprit line.

Read more about Solving electronics repair problems fast using voltage testing here.


  1. After checking for dry joints I would go immediately to the collector resistor R364. Normal voltage on this resistor most likely means that the Green output transistor is not shorted. Otherwise the shorted transistor would cause the collector resistor R364 to drop the total collector voltage. If voltage is present then go to the green cathode. If no voltage is present resistor R361 is probably open. Could also be the small inductor but more likely the 1.5K resistor.