Picture streaking

[W4rtc]

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

[old_tv_nut]

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.

[Phil Nelson]

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:



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

[Boobtubeman]

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

Or about to hose it off

SR

[miniman82]

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

[Penthode]

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?

[lnx64]

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

[Phil Nelson]

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

[old_coot88]

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.

[old_coot88]

OOPs! Double post.

[W4rtc]

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

[bandersen]

I've been using Slip-Plate lately.
A quick fix for flaking CRT coating is some aluminum foil taped in place

[old_coot88]

Originally Posted by W4rtc

...the coating is peeling off the crt. That could be a problem.
Joe

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.

[Tom Albrecht]

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.

[W4rtc]

Hi well I am having no luck at all I have checked and checked all voltages and all seems to be o k. 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.
Joe

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