Advice Admiral 12X12 20Z1 low contrast w/ lines

[rca21d645]

After replacing the vertical output transformer and most of the capacitors, I was able to get a very dim, but visible picture by turning the contrast and the brightness all the way up. I noticed that no matter what I adjusted these lines stayed on the picture. I'm guessing this means there's an issue with either the brightness or the contrast, but I'm not certain. The lines look a lot like the retrace lines that appear when you turn up the brightness too high on older B/W computer monitors, but these lines don't disappear no matter how low the brightness is turned. Audio still comes in just fine.

[rca21d645]

here's a better picture of what it looks like, it shows up better in the dark. I also attached a link to a video of the television here: https://drive.google.com/file/d/1209...ew?usp=sharing

[bandersen]

Looks like a tired CRT or low HV. Are you able to measure the HV ? Should be around 9 kV.

[rca21d645]

Originally Posted by bandersen

Looks like a tired CRT or low HV. Are you able to measure the HV ? Should be around 9 kV.

I don't think I have any easy way of measuring the high voltage as I don't have a high voltage probe, however I do know that the picture tube is fairly worn out but I didn't think that that would cause the retrace lines to appear like that.

[bandersen]

Turning up the brightness and contrast on a weak CRT causes the retrace lines to appear.

Also the image has that ghostly almost inverted appearance common with weak CRTs.

There is a retrace suppression modification that can easily be added.

You can find it in Vol 1 here: https://www.earlytelevision.org/rider_cures.html

[rca21d645]

Originally Posted by bandersen

Turning up the brightness and contrast on a weak CRT causes the retrace lines to appear.

Also the image has that ghostly almost inverted appearance common with weak CRTs.

There is a retrace suppression modification that can easily be added.

You can find it in Vol 1 here: https://www.earlytelevision.org/rider_cures.html

The download isn't working and I think the site hosting it is down, is there any other way to find this guide? Also would a weak tube have retrace lines appear when the brightness and contrast are turned all the way down? Because no matter which way I adjust the brightness and contrast the retrace lines stay on the screen, even if I turn them to the point of no longer seeing a picture.
Edit: I found it using the Wayback Machine

[rca21d645]

I also just noticed that turning the brightness all the way down made the picture clearer but the retrace lines remained on the picture.

[Kevin Kuehn]

Originally Posted by rca21d645

I also just noticed that turning the brightness all the way down made the picture clearer but the retrace lines remained on the picture.

Does your focus control seem to have any influence on the picture sharpness, as in can you make the scan lines more or less defined? Also can you make the CRT go all the way dark using the brightness control? When I say dark I mean can the brightness make the CRT go as dark as when the set is turned off? From what you said earlier about the retrace lines never going away it sounded like the the brightness would not cut off the picture.

[old_coot88]

I don't have a schematic, but there should be about 3 (maybe 4) peaking coils closely adjacent to the video output stage. Have you checked those for continuity?

[Kevin Kuehn]

Originally Posted by old_coot88

I don't have a schematic, but there should be about 3 (maybe 4) peaking coils closely adjacent to the video output stage. Have you checked those for continuity?

Here you can download both Sams and Riders from the ETF

https://www.earlytelevision.org/tv_s...s_admiral.html

[Yamamaya42]

its most likely you just have a very weak CRT,,, have you tested it yet?

[rca21d645]

Originally Posted by Kevin Kuehn

Does your focus control seem to have any influence on the picture sharpness, as in can you make the scan lines more or less defined? Also can you make the CRT go all the way dark using the brightness control? When I say dark I mean can the brightness make the CRT go as dark as when the set is turned off? From what you said earlier about the retrace lines never going away it sounded like the the brightness would not cut off the picture.

Turning the brightness down does not make the tube completely dark, and the focus control does effect the sharpness.

[rca21d645]

Originally Posted by old_coot88

I don't have a schematic, but there should be about 3 (maybe 4) peaking coils closely adjacent to the video output stage. Have you checked those for continuity?

I have not, but I'll check them tomorrow and let you know.

[rca21d645]

Originally Posted by Yamamaya42

its most likely you just have a very weak CRT,,, have you tested it yet?

The CRT did test fairly weak, but like I said I don't think a weak tube would make the retrace lines unable to go away.

[Kevin Kuehn]

Originally Posted by rca21d645

Turning the brightness down does not make the tube completely dark, and the focus control does effect the sharpness.

Well what kind of DC voltage range do you read from the wiper leg of the brightness pot when you rotate it from one end to the other? One would expect approximately 150v at one extreme and 0v at the other. Referenced from chassis ground.