So close - Videokarma.org TV - Video

radio nut · #1 10-01-2012, 12:21 PM

Well I finally got my sears all channel tv working without red plating the vertical tube. But it still has one issue left. Keep in mind that all out of tolerance resistors and paper/ elecrtolytics and been replaced. The set has side to side jitters and as an example if you watch Cheers all of the glasses hanging at the bar twinkle.Well let me try my camera again...looks like I posted the wrong picture.

radio nut · #2 10-01-2012, 12:34 PM

Ok lets try this again. in one of the pictures you can see lines on the left side that run from the top and go down. In the other picture I am really close to the screen But only darker images seem close to sharply focussed.

So my question is what circuit do I check? would it be the high voltage caps mounted on the flyback that are in the yoke circuit or do I look elsewhere?

Zenith26kc20 · #3 10-01-2012, 12:52 PM

From the pictures it looks like an interlace problem. I would look in the sync circuit. Does this set have a power transformer or is it a series string?

radio nut · #4 10-01-2012, 01:25 PM

Series string. This set does have a horiz. stabilizer adjustment that has 2 caps I replaced that were paper. Could this be the issue? This set is Sam's 792 folder 3.

***Eric H*** · #5 10-01-2012, 01:36 PM

I think he's talking about the ringing on the left side of the screen, that would be a problem in the horizontal circuit, bad damper tube perhaps, or misadjusted drive etc...
they can be a pain to get rid of sometimes.

radio nut · #6 10-01-2012, 02:16 PM

Quote:

Originally Posted by Eric H

I think he's talking about the ringing on the left side of the screen, that would be a problem in the horizontal circuit, bad damper tube perhaps, or misadjusted drive etc...
they can be a pain to get rid of sometimes.

The damper tube is nos and rechecked good. my camera is not taking as "smooth" a picture as I would like but the lines on the left side go from the top down and kind of curve towards the center of the screen. this problem started slowly like some component was dying.not all at once. if I just let the set run the picture wiggles from left to right and white objects twinkle.

***Eric H*** · #7 10-01-2012, 06:45 PM

The wiggle would also indicate something in the Horizontal circuit that isn't up to spec.

Are there any capacitors inside the High Voltage cage that you might have overlooked? Also the resistors and capacitors in the Yoke cold be causing problems.

A bad Flyback can also cause this as can a bad horiz output tube.

The white areas twinkling is a separate problem I suspect, does that go away if you turn the brightness down?

White objects taking on a silvery appearance when the brightness is turned up high can be a sign of a weak CRT.

radio nut · #8 10-01-2012, 07:13 PM

Quote:

Originally Posted by Eric H

The wiggle would also indicate something in the Horizontal circuit that isn't up to spec.

Are there any capacitors inside the High Voltage cage that you might have overlooked? Also the resistors and capacitors in the Yoke cold be causing problems.

A bad Flyback can also cause this as can a bad horiz output tube.

The white areas twinkling is a separate problem I suspect, does that go away if you turn the brightness down?

White objects taking on a silvery appearance when the brightness is turned up high can be a sign of a weak CRT.

No on caps in high voltage cage. I was wondering about the 2 +3 kv. caps mounted on the fly that are part of the yoke circuit.

The flyback tests good as far as resistance tests per diagram.

The crt has brightness to spare. If I turn up the brightness all the way the picture will almost go completely bright to where you really can't tell what your watching.

The tubes have all been retested and are good.

Resistors in the yoke: I am not sure how to access them.

There is a horizontal stabilizer adjustment. in that small circuit are two paper caps that I have replaced. Could this adjustment be "out" because of slight capacitance differences with the new caps?

radio nut · #9 10-01-2012, 08:57 PM

I had to re read your reply Eric H. There are 3 high voltage caps in the yoke circuit and I know Fair radio has them in stock so I will replace them and see what happens. I will read the diagram and see how to adjust the horizontal stabilizer also since it was pointed out that the issue is in the horiz. I also will check the sync sep tube and the sync line and see what I come up with.

miniman82 · #10 10-01-2012, 09:48 PM

The bars on the left of the screen are caused by horizontal ringing, usually a symptom of excessive drive. Reduce the drive with the drive pot/trimmer if there is one, if there isn't one you'll have to tweak the values of certain resistors in the horizontal oscillator circuit. Also check horizontal current drain while you're at it (should be a small value resistor on the h-out tube's cathode), it's likely out of spec. A clue will be the height of the waveform going into the h-out tube, so scope the grid and bounce it off the schematic. The other stuff looks like 3.58mhz dot crawl to me, but I could be wrong. If it is, there may be a trap you can adjust in the video chain somewhere. Again, look for a slug you can tweak in the schematic. If there's no 3.58 trap, you'll just have to live with it unless you are able to feed it video from the Y component jack of a DVD player or cable box (the Y line is B&W only, so should provide a clean source).

radio nut · #11 10-01-2012, 10:05 PM

Ok, I do not have a scope now. I will check the resistor in questionand look for a drive adjustment. thanks.
That "fence" type pattern in the close-up picture is not as bad as the picture makes it look. The camera seems to amplify it. If you do not click on the second picture, just sit back from your computer screen then the darker items look shap"er" than anything else.

I have been given things to look for by a few people so I will get busy and post results.
Thanks!

radio nut · #12 10-09-2012, 02:50 PM

Ok, Well I replaced two out of the three yoke caps. One is "in " the yoke and I will just have to get in there.
The Twinkling has stopped and now the lines moving from the top down are pretty much all the way across the screen and the contrast is crap. The set had really good contrast a while ago and now its just gray and gray"er".

So I am guessing that some components are changing value as I work this set. This weekend I will go through the resistors one by one and see what might be off.

There is not a horizontal drive adjustment so I will see what I see as the week progress's.

As far as the 3.58 trap... there is one and I will check the diagram on its adjustment.

miniman82 · #13 10-09-2012, 08:06 PM

Probably will have to peak that 3.58mhz trap, then the checkerboard pattern should get weak if not disappear. This is best accomplished with a sweep generator, coupled through the video amp. The one I have has a switch that will cause 3.58mhz to appear in at the detector, and you can easily null it out using a scope to view the waveform.

ctc17 · #14 10-09-2012, 08:24 PM

3.58 trap? You mean 4.5 trap?

Before you go twisting coils verify its not something in the house interfering with the set. printers, these new electronic ballasts etc can cause that.

Leaky/bad phase diodes can cause the jittering and bars. Leakage in the yoke can cause the bars too.

Just because you changed the paper and electrolytics your not golden. I am seeing more and more leaky/shorted/lossy red and orange drops. The domino style mica. paper/mica are always bad where there is more than a few volts across them.

Just some notes to consider

old_tv_nut · #15 10-09-2012, 09:28 PM

That dot pattern is too coarse to be 3.58. If it wiggles in time with the sound, it's related to 4.5 Mhz, possibly beating with the 3.58. If it doesn't wiggle with the sound, it's something else, but I couldn't guess what. 3 wild guesses: something is oscillating that shouldn't; or the fine tuning is way off and the chroma overloads the video detector; or the IF is distorting.