Zenith, flyback white lines on screen

[M. W.]

Greetings all,

Zenith SJ5504EW early nineties. Problem, retrace vertical
white lines. I measured all voltages and signals on CRT neck board,
nothing suspicious. The B+ voltage is as indicated on schematics
which led me to think that the high tension voltage is not over
the nominal value. I changed up and down G2 voltage, still the
lines appear. Apart from those lines picture is good with color.
In Aux mode (no input signals) I get a nice blue screen no retraces.
My general understanding of the retrace problem is the R, G, B,
video signals will be blanked during the retrace, in horizontal
and vertical retraces, the G2 or second grid voltage will set a
threshold for signals that will be displayed on the screen.
So the problem should be in either the video path or the CRT itself.
I read in this newsgroup that Zenith CRTs of the nineties tend
to break down frequently. Is there a reliable test to exclude
the CRT? Also, what would be the probable causes in the video path?

Thanks in advance

Luka

 

[David]

What is the 200v video output scan derived voltage?
What is the G1 voltage?

If you remove the video output transistors on the crt pcb and still have the
problem and the G2 and G1 are all correct, yes crt.

David

M. W. <w2000@insight.rr.com> wrote in message
news:1d6ef5d4.0312170911.3b64d01a@posting.google.com...

Greetings all,

Zenith SJ5504EW early nineties. Problem, retrace vertical
white lines. I measured all voltages and signals on CRT neck board,
nothing suspicious. The B+ voltage is as indicated on schematics
which led me to think that the high tension voltage is not over
the nominal value. I changed up and down G2 voltage, still the
lines appear. Apart from those lines picture is good with color.
In Aux mode (no input signals) I get a nice blue screen no retraces.
My general understanding of the retrace problem is the R, G, B,
video signals will be blanked during the retrace, in horizontal
and vertical retraces, the G2 or second grid voltage will set a
threshold for signals that will be displayed on the screen.
So the problem should be in either the video path or the CRT itself.
I read in this newsgroup that Zenith CRTs of the nineties tend
to break down frequently. Is there a reliable test to exclude
the CRT? Also, what would be the probable causes in the video path?

Thanks in advance

Luka

 

[GPG]

w2000@insight.rr.com (M. W.) wrote in message news:<1d6ef5d4.0312170911.3b64d01a@posting.google.com>...

Greetings all,

Zenith SJ5504EW early nineties. Problem, retrace vertical
white lines. I measured all voltages and signals on CRT neck board,
nothing suspicious. The B+ voltage is as indicated on schematics
which led me to think that the high tension voltage is not over
the nominal value. I changed up and down G2 voltage, still the
lines appear. Apart from those lines picture is good with color.
In Aux mode (no input signals) I get a nice blue screen no retraces.
My general understanding of the retrace problem is the R, G, B,
video signals will be blanked during the retrace, in horizontal
and vertical retraces, the G2 or second grid voltage will set a
threshold for signals that will be displayed on the screen.
So the problem should be in either the video path or the CRT itself.
I read in this newsgroup that Zenith CRTs of the nineties tend
to break down frequently. Is there a reliable test to exclude
the CRT? Also, what would be the probable causes in the video path?

Missing vert blanking from vert o/p.
Thanks in advance

Luka