## Saturday, December 10, 2011

### Telefunken TV with colored spots on the screen

Thulani: How are you sir? I have encountered a problem with a Telefunken TV, l think the problem is on RGB circuit, the picture is there, it shows three colors which is red on the four corners, blue and green on the center screen. When l check the main RGB volts 200v and on board is 180v.the RGB is from FBT

Humphrey:The question is not clear to me Thulani, can you send me the picture of the same. Having said that could it be that you repaired the TV and never returned the degaussing coil? This is very important because it is used for cleaning the screen from any magnetic effects (colored screen). Also be sure there is no speaker near the TV screen.
I don’t suspect the RGB circuit for now….
Please let me know if you are successful

Thulani:The posistor when is working suppose to heat up and when short blows the fuse, degaussing coil is connected and when l switch the TV to AV l
see three colors red, green, blue. When l do voltage test on main RGB supply l measure 200V while on board is written 180V l suspected the RGB transistors and replaced them the problem was not solved.

l don’t know where to go from here and is my first problem

Humphrey:That’s  why I told you to send me a picture of the screen, you can use even phone camera. the voltage at the RGB seem to be high(180v) so I expect the screen to be blank(dark) so I suspect still you measurement are not right.. What is the voltage at the both sides of the RGB resistors...and at the actual cathode pins..

Thulani: He is the screen picture sir.

Humphrey: Hi My friend Calvin, This problem only point to two areas.
2.Degaussing circuit

Thulani: Used a demagnetizer no change by substituting the CRT solved the whole problem to me it was a lesson...Thank you.
Another  question I been repeating this amazing book and I still don’t understand the dummy load every time when I found the output voltages  are low I will identify the B+ and substitute with the bulb and it  will remain off the question is should I rejoice at the results? I don’t understand

Humphrey: Thanks for that success report Thulani...congratulations!!!

With regard to dummy load, I suggest you take a  good working Television  set, Dis-connect the B+ load just before the flyback pin where this B+  enters the primary coil of the flyback and attach the 60 watts bulb  there(one pin of the bulb on B+ line and the other leg on the cold  ground  eg tuner ground).

You will find that the bulb will lights steadily and you will be able to test the voltage across the B+ (usually 90 volts dc and above) with this then you will be able to know how a good supply behave.

If you find the actual B+ is low and you substitute with a dummy load and still the voltage is low then suspect primary side of the power supply.

If the voltage goes up and the bulb has a steady lights then the problem is on the secondary side.

Kind regard

Humphrey

Author CRT Television repair Course