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-   -   More screen anomalies (http://www.videokarma.org/showthread.php?t=259446)

TinCanAlley 09-08-2013 12:33 AM
More screen anomalies
 
1 Attachment(s)
Okay, I'm at the end of what I can do and have followed every suggestion. Not only do I still have the very distracting jail bars, but I also have some other anomaly that kind of looks like what you see when they show the magnetic field of the planet.

I have check for every possible interference from the RF unit all the way to the IF inputs. I have tried rerouting the wires around the antenna leads and still they persist. They do seem to change shape with certain changes in brightness, but that might just be them becoming harder to see.

I did my best to capture them on screen. You'll see them quite clearly (as well as the massive jail bars).

I really had hopes of making this set my main one, but if I can't get her looking good she's going into storage. With the convergence problem, this makes three that are distracting me from enjoying the picture.

lnx64 09-08-2013 01:01 AM
That's odd looking, looks like moire patterns.

Dude111 09-08-2013 01:43 AM
Looks like it could be interference.. (RF)

Is there anything near your TV buddy??


Good luck!

zeno 09-08-2013 08:23 AM
Quote:
Originally Posted by lnx64 (Post 3081655)
That's odd looking, looks like moire patterns.
Yes its moire. not rare in that vintage CRT. Not much you can
do for it, adj bright, contrast, focus can help sometimes.
With that blank picture you should go along the video chain &
look for where the jailbars start with scope.

73 Zeno:smoke:

DaveWM 09-08-2013 10:16 AM
since you have already chased horz blanking, another long shot, the damper diode on the horz out.

andy 09-08-2013 10:59 AM
...

Username1 09-08-2013 11:17 AM
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This is some interference from a ringing of a sharp blanking diode, or transistor, or damper, etc. that is not decoupled properly. Take a scope and see if you can see it on the power supply near the video amp transistors.

Did you re-cap this set?

TinCanAlley 09-08-2013 02:44 PM
I don't think I'm the first to try and fix the jail bars. The more I check the horizontal, the more evidence I find of someone else going the same route. The first was the diode in the blanking circuit. It had already been cut and soldered back together. Now I see that someone cut and resoldered the leg of the boost rectifier (CR219). I'll have to get back under the chassis to see if they also did the same to the damper (CR218) on the horizontal output. I'll also look at the booster rectifier (CR221). They're all the same part number: 103-193. I haven't been able to find NOS, but NTE makes a replacement (NTE506).

TinCanAlley 09-08-2013 02:45 PM
Quote:
Originally Posted by Dude111 (Post 3081658)
Looks like it could be interference.. (RF)

Is there anything near your TV buddy??


Good luck!
Nothing near it. I also made sure nothing else was around the RF modulator. If I connect the RF to my other CCII, the pattern isn't there.

TinCanAlley 09-08-2013 02:47 PM
Quote:
Originally Posted by andy (Post 3081668)
You could try defocusing it slightly to reduce the moire. TVs of this age can look very good, but it's never going to match a decent modern set. If you want the best CRT set you can get, look for a Sony XBR from the 90's, or newer.

For the jail bars, I think it's clear that you're not going to fix it by shot gunning parts. It's going to take a good oscilloscope and someone who knows how to use it. That old scope you have won't cut it for finding a subtle problem like this. I would start at the CRT socket to see if the jail bars are on the cathodes, G1, or G2 (careful that you don't exceed the voltage limit of the scope and probe with the G2, a HV probe might be needed).

If there's nothing on the CRT socket, then you probably have a horizontal deflection issue (a slight change in the scanning speed as the beam goes across the screen will cause a change in brightness).
I wish there were a place in Los Angeles that rented scopes. I did find one place, but the cost of renting for a week was close to buying a used one (of course buying used is risky as most lower cost units are "untested").

TinCanAlley 09-08-2013 02:50 PM
Quote:
Originally Posted by Username1 (Post 3081670)
This is some interference from a ringing of a sharp blanking diode, or transistor, or damper, etc. that is not decoupled properly. Take a scope and see if you can see it on the power supply near the video amp transistors.

Did you re-cap this set?
I went through and replaced all transistors in blanking, video output, amps, etc. There was no change and I put all the originals back and kept the new for backups. I replaced the blanking diode and the resistors that work with it, but that didn't help. That leaves the three diodes around the horizontal output and I'll be ordering them tomorrow.

Username1 09-08-2013 02:57 PM
That is coming from inside the set. And it is coming from the horizontal circuit somewhere. It is easy to see because it occurs regularly and keys off the horiz. sync.
it is occurring 10 times or there about during the scan. So from the pulse to trigger the 1/15734 it is allowed to "ring" and cause interference. This could be a poorly decoupled r/c, or, l/c circuit. You would need to check waves with a scope, look for fuzzy waves, there could be a ringing, that you would have to look up at that frequency for.... 10 in the space of 1/15734 That is a ringing of a pulse..... Look for decoupling caps where there are high voltage 1/15734 pulse....

TinCanAlley 09-08-2013 03:11 PM
Quote:
Originally Posted by Username1 (Post 3081684)
That is coming from inside the set. And it is coming from the horizontal circuit somewhere. It is easy to see because it occurs regularly and keys off the horiz. sync.
it is occurring 10 times or there about during the scan. So from the pulse to trigger the 1/15734 it is allowed to "ring" and cause interference. This could be a poorly decoupled r/c, or, l/c circuit. You would need to check waves with a scope, look for fuzzy waves, there could be a ringing, that you would have to look up at that frequency for.... 10 in the space of 1/15734 That is a ringing of a pulse..... Look for decoupling caps where there are high voltage 1/15734 pulse....
Forgot to let you know that I did recap the entire chassis except for the sound board. There isn't an old electrolytic left. I even changed them on the bipolar one on the video processor module.

I'm trying to get my hands on a better scope. It was hard enough for me to find the waveforms with the scope, but if I have to count them, I might lose my mind. :) Maybe I can get them on this scope. I'll give it a try, but I'm sure the only hope is a better scope.

andy 09-08-2013 03:32 PM
...

TinCanAlley 09-08-2013 04:04 PM
Quote:
Originally Posted by andy (Post 3081690)
It could be a ceramic cap, or film cap. It could also be a circuit that's not grounded well, or that is grounded to the wrong place.
So I should look at all the caps that go directly to ground in the horizontal circuit?


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