Picture streaking
 

Hi
O K this is my first TV restore. I have replaced all caps and most of the resisters. It works good execpt the sreaking of the picture. I will try to attach some pictures. It seems to be worse when the contrast is up a little high. The set has good contrast and brightness. The chassis is Admiral 21C1 model 36R45. The set has not been aligned and all voltages check very close to correct. Any help will be appreciated. This set had many bad resisters I replaced most of them it had a lot of resisters in series to make the correct value as per the prints. Thanks
Joe

http://i927.photobucket.com/albums/a...ps268396b0.jpg

http://i927.photobucket.com/albums/a...ps13d2b70d.jpg

Second pic looks like high amplitude video is affecting the vertical sweep somehow.
Not sure why it wouldn't screw up the horizontal at the same time.

Just a wild guess:
Try playing with AGC.

Overloading video was also my thought when looking at those screens. Too much gain might mess up the sync, and thus sweep.

I believe the Riders manual for Admiral chassis 21C1 is at ETF:

http://www.earlytelevision.org/tv_sc...s_postwar.html

I don't see an AGC adjuster in a quick peek at the schematic, but the manual does have this note:

http://www.antiqueradio.org/art/temp...1C1AGCNote.jpg

AGC may be as good a place as any to start checking. Some of my sets are quite sensitive to the signal strength from different sources. In addition to adjusting the Picture control, you might also try out different sources, if you have any (DVD player, VCR, digital converter, signal generator, etc.).

Phil Nelson

Could just be the angle, bit it appears like the bridgestone dude is about to make a nasty gesture at that car :D

Or about to hose it off :D

SR

Almost looks like vertical folding to me, maybe try playing with the heigh/linearity controls?

Looks like the peak white video is modulating the vertical sweep. Try first adjusting the contast control. If reducing contrast improves this, I would suggest checking the B supply, especially looking for a common electrolytic between video amplifier and vertical output supply feeds. Or perhaps a common supply series resistance has increased in value?

I don't think the picture is folding over in the 2nd pic. Looks like a widescreen commercial to me.

Look at the topmost line of text in the second screen. The tops of the letters are missing, as if several lines of video got folded into one or two, making the bright horizontal line. I don't know if you call that folding or whatever, but something is disturbing vertical timing in an irregular way from top to bottom.

The contrast also becomes greater immediately below that line. Look at the patterns in the trees at the right.

Phil Nelson

For the heck of it, check to be sure the aquadag (conductive coating) on the CRT is securely grounded. A ungrounded or poorly grounded 'dag can cause some really wierd symptoms mimicking AGC and sync problems.
A little factoid worth bookmarking for future referance even if not applicable to this particular problem.

OOPs! Double post.

Hey guys thanks for the replys. Yes coot88 the coating is peeling off the crt. That could be a problem. Bob sprayed something on a crt that was conductive I will try that, alto I cannot find a place to buy it here in Louisville. I will have to try to get it on line. Can't recall what it is called but will look it up. I have checked voltages all around the video circuits and they are very close to the what they should be, I have a good set of info on this. Thanks to all for replys.
Joe

I've been using Slip-Plate lately.
A quick fix for flaking CRT coating is some aluminum foil taped in place :)
http://farm8.staticflickr.com/7257/7...10cba2b1_z.jpg

Yeah, the inner and outer coatings of the CRT form the plates of a capacitor which is the filter cap for the HV supply itself. If the outer (negative) coating loses its ground connection, the HV loses its filtering. This can allow the HV to fluctuate instantaneously with beam current. Sometimes there's also arcing from the 'dag to ground, and this can be picked up in the RF or IF chains, further screwing with the pic.

I'm also very interested in understanding this phenomenon. I have seen this on multiple different sets, both electrostatic 7JP4 sets and on some 10" and 12" sets. The observed phenomenon is that the vertical sweep gets compressed on lines with very bright features. I have never been able to trace down what causes it. Looking forward to seeing what gets figured out here.

On 7JP4 sets, I've tried adding multiple extra capacitors to help stabilize the HV, but it has no benefit.

The most recent set I saw this on was a metal CRT Zenith, so aquadag is not the issue for either of these two examples.

Hi well I am having no luck at all I have checked and checked all voltages and all seems to be o k. :scratch2: I am not the smartest person when it comes to using a scope but what I can see is the patterns look good on the scope. I cannot figure what is happening. You are correct when the contrast is up high the scanning lines pinch up and turn bright and the line is lost to the bright line, turn the contrast down and it will stretch back out normal. I think I will take off a while and maybe when I come back to it I will find something. The set could use a alignment but I don't have the generator to do that. I don't think alignment would fix the problem. Oh well I guess I will find something. Any help will be appreciated. :yes:
Joe

coot88 I did put a coating on the crt and it did not cure the problem thanks for the suggestion tho

I am getting more curious too. What do you see if you put the scope on the B+ that feeds the vertical? Does the vertical section get power from the horizontal some way, like from B+ boost? (Trying to guess how extreme brightness could affect the vertical.)

FWIW I've experienced this with a 16" metal cone tube.

Looks like the whole vertical section runs off the boosted B+ supply. I still vote for video leaking into the vertical sync circuits. If the boosted B+ was unstable, I'd expect to see non-linear horizontal sweep, plus trace dimming and blooming as well. I'd take that scope and look at the sync signal at R401. Also, look at the grid of the 6S4 and see if tou have a decent sawtooth waveform there.

If you don't have a clean ramp-shaped signal, I'm gonna push you out on a limb and (with others agreeing, it's not my TV here) suggest lifting one end of R 401 and see if you can get the vertical oscilator to sit still long enough to see if that clears up the distorted sweep.

One more thing. Did you REALLY check your work when you were done? It just takes one wrong-value part or one wrong connection to mess it all up. Just for the heck of it, recheck the vertical and sync circuit wiring really close. Good luck!

Well I think I found the problem, at least on my set. In restoring the set I put the retrace line mod in to remove the retrace lines. Well I removed the mod and now the picture is o k at any setting of the brightness or contrast setting. I put the mod back in and the pinching of the scanning lines came back. On my set I dont really need the mod as the retrace line are not there unless I turn the contrast way down. So I will most likely leave the mod out. Or I may try some different size components. But for now I have a beautiful picture. Thanks for all the help. I do need a alignment tho guess i will have to ger me a sweep generator. OH well. Thanks
Joe

Could you post a partial schematic with/without the retrace mod? I would like to understand this for future reference.

Hi OTN
Here is the best I can do I am not too good with making computer drawings so I did it by hand hope this helps.
Joe

http://i927.photobucket.com/albums/a...psa9cda6e2.jpg

Hmmm - maybe the peak whites are drawing grid current on the CRT, and affecting the vertical grid voltage of the vertical output? A bigger value for C310 might change things, but not fix them. Too big a value would filter out the pulse that is intended to blank the retrace lines.

If you could find a negative vertical retrace pulse somewhere else, it might work and not affect the vertical sweep.

Another thing to try would be some resistance in series with the added .05 capacitor.

Hi
Well I replaced the .05 cap with a 900 mmf in the mod and the retrace lines are gone and the picture is great. I still get a small amount of " pinching with contrast all the way up" but 100% better with the change. I watched some of the Super Bowl and the picture was very good. :banana:
Joe

Glad you fixed it. It would be interesting to know what the pulse on the CRT grid looks like now. Reducing the cap should have reduced both the pulse amplitude and the feedback to the vertical about 50 times.

Hey -- I think you guys are on to something here! I've noticed that both the brightness and the contrast affect this bunching effect in sets that have it. Grid current in the CRT would indeed correlate to that. I'll have to put one of my sets that show this problem on the bench and go after it when I get a chance. I wonder if I have created this problem by adding my own blanking circuits to certain sets?

O K I had to take the mod to eliminate the retrace lines out. I tried many different combinations of caps and resisters, with any combination of caps and resisters it still had streaking. On the dark scenes the streaking was very bad, but take the mod out and it was o k. Just putting the resister in the mod and not the cap the streaks were there, and I tried many sizes of resistance.
Joe