A thin white line across the raster Admiral TV 1948 model 17T12

[recepteur]

Good evening old_tv_nut,

I did not noticed any distortion, see enclosed pics.

This effect is present with a picture as with a plain raster.

This particular thin white line is transparent, sort of a clear mask and you can see the picture details behind it.

Vertical scanned lines are evenly spaced.

Cheers

[old_tv_nut]

Well, that all says it's a blip in the video, or at least on some CRT electrode besides the deflection.

[old_tv_nut]

You could try disconnecting C43, .05 video coupling, to see if it's coming in that way. If it's still there, maybe bridging another 20 uF across C32a in case that's bad.

[recepteur]

Good day old_tv_nut,

Thanks for your input, I will proceed with your recommandations and will share my findings. Cheers

[recepteur]

Good evening old_tv_nut,

Disconnected C43 .05 couping capacitor and also bridged C32a did not erase the thin white line. Cheers

[old_tv_nut]

Originally Posted by recepteur

Good evening old_tv_nut,

Disconnected C43 .05 couping capacitor and also bridged C32a did not erase the thin white line. Cheers

Well, I'm out of ideas then.

[Electronic M]

Have you tried swapping the video stage tubes and deflection stage tubes. If there is heater-cathode leakage that could cause it and or other strange symptoms.

It might also be worthwhile to feed it a blank raster and check video and deflection waveforms at the CRT. Video should be just sync pulses if you're feeding it a blank raster and deflection should be a clean sawtooth. If you see anything else especially if it is a short pulse then you have found the line the noise is on (then comes figuring out what on the line is causing it).

[old_tv_nut]

Originally Posted by Electronic M

...
It might also be worthwhile to feed it a blank raster and check video and deflection waveforms at the CRT...

Caution about checking the deflection waveforms - they are riding on a high DC voltage at the CRT and could fry your oscilloscope. Scope them at the plates of the deflection tubes instead.

[recepteur]

Gents,

Thanks for your inputs.

I will check the deflection waveforms directly from the plates of the deflection tubes.

Cheers

[old_coot88]

Absence of any compression or folding of scan lines would imply the blip's not deflection-related, but is modulating the CRT beam current. It could be a negative-going blip on the cathode (not likely since you've already isolated that), or a positive-going blip on the focus electrode (pin 5) or the accelerator(?) electrode (pin 9).

[jsandlin]

I have a 7JP4 with a white line across it like yours not quite as vivid as the one on your tube. This is in the tube because the set the picture was taken on has another tube with no line I just hooked this one up to show the line. I don't understand what it is because if it was from no vertical deflection it would be a dark line as stated in another post. just though I would throw this out because of having another tube doing the same thing.

[old_tv_nut]

This really is a head-scratcher to me.

[old_tv_nut]

Is the white line always stationary with respect to the tube face, or does it move with the vertical centering adjustment? If it moves, does it move the same distance as the picture or a different distance? (Trying to figure out if it's a fixed phosphor defect or electrical.)

[jsandlin]

Mine is definitely a phosphor defect there is no movement with any adjustment

[recepteur]

Hello Jsandlin,

Your enclosed picture depicts the same thin white line as on my picture tube.