Advice Admiral 12X12 20Z1 low contrast w/ lines - Videokarma.org TV - Video

rca21d645 · #1 01-20-2021, 03:31 PM

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 · #2 01-20-2021, 06:42 PM

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 · #3 01-20-2021, 06:51 PM

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

rca21d645 · #4 01-20-2021, 06:54 PM

Quote:

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 · #5 01-20-2021, 07:45 PM

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 · #6 01-20-2021, 08:19 PM

Quote:

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 · #7 01-20-2021, 09:36 PM

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 · #8 01-20-2021, 10:10 PM

Quote:

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 · #9 01-20-2021, 10:52 PM

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?

rca21d645 · #10 01-21-2021, 12:07 AM

Quote:

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.

Electronic M · #11 01-21-2021, 01:59 AM

Was the weakness emission, cutoff or both?

rca21d645 · #12 01-21-2021, 11:07 AM

Quote:

Originally Posted by Electronic M

Was the weakness emission, cutoff or both?

It had weak emissions but the cutoff seemed fine

Yamamaya42 · #13 01-21-2021, 08:36 AM

I have the same CRT in my FADA, but it's hooked in differently, the cathode on mine is grounded, and video fed into G1.

The voltage readings for each pin on yours is listed on the SAMS, also you need to be sure you have a good video to the cathode, not sure what it will be for yours, but mine was about 39v PtP, my guess yours should be about the same, but inverted, since its going to the cathode, as opposed G1 on mine.

You also need to find a way to check that you have good HV, if it is low, it may be causing you problems, and/or a misaligned / weak ion trap.

But however, if all checks nominal, you most likely have a very tired / dead CRT, and must find another, and most likely end up paying way too much to some fool on Ebay, like.

https://www.ebay.com/itm/Vintage-Syl...-/174589841825

rca21d645 · #14 01-21-2021, 11:32 AM

Quote:

Originally Posted by Yamamaya42

I have the same CRT in my FADA, but it's hooked in differently, the cathode on mine is grounded, and video fed into G1.

The voltage readings for each pin on yours is listed on the SAMS, also you need to be sure you have a good video to the cathode, not sure what it will be for yours, but mine was about 39v PtP, my guess yours should be about the same, but inverted, since its going to the cathode, as opposed G1 on mine.

You also need to find a way to check that you have good HV, if it is low, it may be causing you problems, and/or a misaligned / weak ion trap.

But however, if all checks nominal, you most likely have a very tired / dead CRT, and must find another, and most likely end up paying way too much to some fool on Ebay, like.

https://www.ebay.com/itm/Vintage-Syl...-/174589841825

Is the 12LP4A a common tube, would it be possible to find someone willing to sell one on here?

Yamamaya42 · #15 01-21-2021, 11:55 AM

Quote:

Originally Posted by rca21d645

Is the 12LP4A a common tube, would it be possible to find someone willing to sell one on here?

All you can do is ask in the classified area, and hope, and you do not have to limit yourself to a 12LP4A exactly, if you find a 12LP4, ( same CRT, but without the gray face ) you could use that, or some other compatible one, for example a 12KP4 will work, just leave off the ion trap, I'm sure there are others that can work as well.

Also, when I was bringing up my FADA, I did not want to risk hurting my 12LP4, so I used a 8YP4 Test CRT that I got from ETM, not exactly the right one to use, but it worked for me with some minor mods!

you can see it all here :p
http://videokarma.org/showthread.php?t=272325