(CRT)QUADRO CTV-5525 ,Horizontal white lines problem

[microcont]

Hello, so I have this TV with the problem that on screen are these white lines .. so i tired to look around board but everything seems okay except some bad soldering joints that was resolder but problem is still here, this is not a priority repair i just what to learn something about CRT TV's. About CRT TV's I know only basic working principle from school. So thanks guys i can post more pictures of board,electron gun and so on.
Thanks

[tom66]

Re: (CRT)QUADRO CTV-5525 ,Horizontal white lines problem

This is usually caused by a fault in the circuit that blanks the electron beam during the vertical re-trace stage of the CRT scanning.

[microcont]

Re: (CRT)QUADRO CTV-5525 ,Horizontal white lines problem

So fault is probably in that circuit , where to find that part of circuit and is there any special part to look for?

[freakaftr8]

Re: (CRT)QUADRO CTV-5525 ,Horizontal white lines problem

you could always check and see if the screen adjustment on the back of the TV if it's accessible has not been tampered with more known as G2 adjustment I've seen people over drive these because the CRT is starting to get weak.

[microcont]

Re: (CRT)QUADRO CTV-5525 ,Horizontal white lines problem

on the flyback transformer are two knobs for adjustment focus and brightness

[tom66]

Re: (CRT)QUADRO CTV-5525 ,Horizontal white lines problem

Try the brightness control first.

[Ltank]

Re: (CRT)QUADRO CTV-5525 ,Horizontal white lines problem

I believe your horizontal frequency is too high. Check the oscillator circuit. Should be 17,750 hz if I remember correctly.

[microcont]

Re: (CRT)QUADRO CTV-5525 ,Horizontal white lines problem

try to adjust knobs on flyback transformer no results only changing brightness and sharpness, huh,i can't measure frequency because i dont have an oscilloscope :/ i can change parts in oscillator circuit

[R_J]

Re: (CRT)QUADRO CTV-5525 ,Horizontal white lines problem

Look for a capacitor near the flyback or near the vertical circuit. should be a low value 2.2 3.3 10 or 22 uf at a high voltage 200, 250 volts, It won't look bad but most likely is, ther may also be a couple bad caps arount the vertical output that could be weak
Looks like it could be C706 1uf 250v

[microcont]

Re: (CRT)QUADRO CTV-5525 ,Horizontal white lines problem

at the output to the electron gun board it is 10uF 250V. It is very dusty trying to clean that..

[microcont]

Re: (CRT)QUADRO CTV-5525 ,Horizontal white lines problem

vertical IC is:

http://www.rem-tv.odessa.ua/datasheets/v_def/LA7840.pdf

[R_J]

Re: (CRT)QUADRO CTV-5525 ,Horizontal white lines problem

It looks like this might be a closer diagram, the dust won't cause the problem. on this diagram its c303

[microcont]

Re: (CRT)QUADRO CTV-5525 ,Horizontal white lines problem

I change that cap, but no results still is the same screen with lines as before

[microcont]

Re: (CRT)QUADRO CTV-5525 ,Horizontal white lines problem

TV works after testing resistor R322 0.68Ohm to find out that it is an open circuit , and i replaced R322 with new 0.51Ohms. It works fine.
Thanks guys for help

[R_J]

Re: (CRT)QUADRO CTV-5525 ,Horizontal white lines problem

If that cap C303 was bad, then there may have been excesive current through d305 causing R322 to open, Bet the cap was bad I have replaced this cap. in more sets than I could count for having retrace lines in the picture.

[tom66]

Re: (CRT)QUADRO CTV-5525 ,Horizontal white lines problem

Yep, resistors rarely fail without obvious cause.

[microcont]

Re: (CRT)QUADRO CTV-5525 ,Horizontal white lines problem

Now it is new C303 and R322 hehe thanks for the explanation , i will remember that fault on TVs