Joined: 06 Feb 2006
|Posted: Mon Feb 13, 2006 6:58 pm Post subject: Grundig ST-70 574 SAT--CUC 5820
|I make a post a week ago about a thermic problem, problem who now it is turn out to be a total failure of TV-set.
First symptom occure a year ago: high level of brightness and an intense white image of a program produced geometrical deformation of picture( a shape like an S of the vertical edges). I decreased the values of brightness and contrast to obtain a corect picture.
6 months later, the problem got worse: if the room temperature was above 25 Celsius, the image on the screen start flickering( a very intense white line flashing on the screen, like a stroboscope). In order to eliminate this annoying efect, i decreased even more the levels of brightness and contrast, or/and opened the room window to lower the room temperature.
Finally, about 2 days ago the image started to disappear and reappear almost immediate until it was gone for good ; the remote and local controls are working and the sound is still OK, except some times is noisy- like a tunner off line.
A visual exame revealed the isolation of the high voltage focus cable was burned ( i dont know if compromised) because it was touching the radiator of the vertical amplifier.
Some multimeter data: power supply is OK( +A=161V; +G=26V; +B=12V; +E=8V; +H=5V) but the voltage recover from the final transf is null( +C= 0 V --corect is 200V). Also, it is not any high voltage and the tube filament it is not on.
The circuit who deliver +C voltage for final RGB amplifier is OK( R528, C529, D529, C527), the BU508A and its circuit is OK, other electrolytic capacitors from the frame stage are OK.
Should i change the starter TDA8140 or should i'll be looking in another place?
If you have any ideea, please, let me know. I only have a multimeter.