More screen anomalies
 

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.

That's odd looking, looks like moire patterns.

Looks like it could be interference.. (RF)

Is there anything near your TV buddy??


Good luck!

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:

since you have already chased horz blanking, another long shot, the damper diode on the horz out.

...

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 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).

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.

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").

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.

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.

...

So I should look at all the caps that go directly to ground in the horizontal circuit?

I'm trying to locate the three diodes in the horizontal circuit and easily found the one on the horizontal output. Here's the thing. The one on the output (CR218) looks just like a diode should (as far as my knowledge goes they're cylinders) and so does the boost (CR219). However, the other boost (CR221), which is the same part number as the other two, looks completely different. It's similar, but looks pregnant. Is this the same thing, and just an different manufacturer?

I'm attaching an image of what I found in the place the SM says is the CR221 (part # 103-193).

Yes, that sure is a diode. Now I'll throw my two cents in... it sure looks like you have a 'ring' in there somewhere... have you checked the yoke for any caps??? It would be a perfect L-C circuit to oscillate... just a thought. I'll make it four cents... take a trip to a hamfest and buy a decent triggered scope with a calibrated timebase and some high zoot probes... sure would make life easier!!

Best of Luck!!

Jim

Found no caps in or around the yoke.

Figures, the Hamfest here is this month and I'm not able to go those days.

So any idea why that diode looks completely different than the other two when they all have the same part number?

Most likely a different manufacturer, same ratings. My 75 Chromacolor II has several of those little bead Diodes as well as some regular barrel type.

...

This really is a job for a first class scope.

Look at the video output to the picture tube and the input to the horizontal
output tube. Also examine the output of the horizontal output tube
BY HOLDING THE PROBE CLOSE TO THE PLATE LEAD but NOT touching it.
Look for the ringing. Then simply remove the horizontal output tube and see what
happens to the waveforms. Make sketches of the waveforms and report back. Use
the grid of the horizontal output tube for sync of the scope.

If its an AC-DC set you can't pull the horizontal output tube ... in that case,
disconnect the plate cap lead.

That's the first step.

its a zenith solid state, so don't pull anything to test with it running.

I agree with the others about the use of the scope, this gets back to having a scope and a lot of knowledge to know how to use it. With out it I was taking a guess at the damper. I don't have a lot of exp with SS sets, so take it for what its worth.

This is a SS chassis. I did all the waveforms and they, to the best of my scope's ability, resembled the forms in the SM. The scope was designed in the 50s and was meant for TVs, still I don't think it's up to the job. I'm going to keep an eye out on ebay for a used scope.

I don't mind testing and replacing parts. That give me more practice at repairs. Until/unless I get a good scope, it's all I can do.

Why don't any of you experts live in SoCal. :(

I'm going to flip her over and check out that diode. Want to make sure it's the right one for the job. I would imaging there's some kind of part number on it.

http://www.ebay.com/itm/GE-511-SILIC...-/171053066177


you may just look for a NTE506

The info I got off the diode is: GI833B. Seems it's a General Instruments diode, but that's all I can find. There isn't any information from the 833B (or no B). It's not listed as a substitute in the SM. Just trying to verify it's the right one for the job. I can't tell if it's original, but it might have been a replacement. The solder in both terminal posts seems disturbed and there's a blob of solder on one end.

I'm trying one last source for NOS, if not, RS has them for 2.50 each w/free shipping. That's cheaper that all other sources that want about 1.30 each, but roughly $9 shipping.

You need to get off the diodes, If it is a diode, not likely, you will have to replace it, they will test ok, but this problem is showing up at a frequency you can't replicate with a tester out of circuit.

Its some decoupling cap, or an RC, LC, circuit. Most likely an LC, yoke, possibly, High Voltage transformer greater likelyhood, Decoupling cap, some cap near an LC circuit running to ground. There are caps with a mark indicating "outside foil" this in most cases went to ground, when you recapped, did you replace using marked "outside foil" caps, and put them in the right way? (These will not be electrolytic caps, but the smaller caps.) This can be a cause of interference.

If you use a scope to try and find this, it will have to be a good one to see the ringing, it will be a pretty high frequency. You will have to have a good probe, and it will also have to be calibrated to the square wave test point on the scope, that way your probe does not effect what you are looking at.

And someone said grounds, look at grounds if there was someone in there before you doing poor solder joints.

I only did the electrolytic caps.

Do you have access to the Sams for the 25EC58 chassis? I think if you could point out where and LC or decoupling cap is in the horizontal circuit, that would help greatly. I think I understand the concept, but unsure when I look at the schematics. I see a 15ohm coil on the boost line and to a .47 cap to ground. Am I looking at the right stuff?

I'm still quite green with all of this, so hang in with me. :)

The moire' patterns occur where the focus is a little too sharp and the scan line structure beats with the CRT screen structure. You can show this easily by adjusting the focus in and out or even by adjusting the vertical linearity or height slightly to change the line spacing. Nothing can be done to fix this.

Regarding the jail bars: I lost track of what set this is and how it's constructed. If it has more than one printed circuit board, make sure all the boards are well grounded to the chassis at their ground points. The ringing frequency will be well within the capability of almost any scope - it looks to be 10 or 12 times horizontal, so that's 200 kHz at most. The problem is, if it's getting into the video and caused by ground currents, the scope would need to be hooked to the same ground point and hot point as the video circuit to see whatever the video circuit is seeing. So, you have a huge number of possibilities of how to hook up your scope. Also, it may be difficult to see if it's getting in at a low-level point in the video circuit and your scope does not have much gain.

As others have said, it might not be in the video, but on one of the CRT electrodes. Does the strength increase and decrease as you turn the contrast (picture) control? If so, it's in the video. If not, it may be getting to the CRT through some other path, or getting into the video after the contrast control.

If there are multiple printed circuit boards (or just multiple ground points on one board), it may be worthwhile to connect some of them to each other or to the chassis with ground wires and observe what happens to the jail bars when you do so. You may find some hot spots this way.

Good luck!

There are five boards press fitted on the chassis. I have removed each one, cleaned them, their contacts and reseated them. No effect.

If I crank up the contrast, the dark bars get lighter until the match the existing lighter bars. So if I crank it up, the entire screens becomes over saturated and it's pretty hard to see the bars (pretty sure they're still there).

Should I be looking for ground points only in the horizontal circuit? It's pretty crazy trying to find out all the ground points on all the terminal strips and such. Only the ground points of the modules are noted. All others have to be located manually. Not an easy process.

I'm going to replace the voltage divider as the current only is leaking. On humid days it buzzes and has a blue corona. If you put your finger near it, it tries to reach out and touch you. Could this cause the moire?

I believe the scope I am using goes up to 500 kHz. I also got a new x10 probe. I just have to figure out what ringing would look like when comparing the wave I get to the one in the SM.

Forgot to mention that I've reduced the vertical height as much as possible without making the top band (I don't know what that black band is called) visible. Does this do anything to the moire?

I have never tried this, but I would think that changing the angle between the scan lines and the screen structure would change the moire' pattern... perhaps try rotating the yoke slightly and re-examine the pattern. Is the scan level?

jr

Not sure what you mean by "saturating?" Do you mean the whole picture gets brighter? Does the bar pattern stay visible if you crank up the contrast AND turn down the brightness (to prevent "saturating")?

My suggestion is to try connecting known ground points directly to where they are supposed to go in case the connectors on the PC boards are still not making good contact even though you cleaned them. Also, you can try connecting different ground points on the PC board connectors to each other to see if that helps.

What is the maximum gain (volts/division) that your scope has? Depending on where in the circuit, you may need more gain than your scope provides to see this waveform, especially if you use a 10x probe.

Your scope needs to be synced to the horizontal sweep. If you cannot sync it independent of the probe input, it will be next to impossible to trace the waveform. You definitely then need a better scope. If the scope is locked to horizontal sweep and showing at least one complete sweep cycle, the jail bars will appear as a sine wave of decreasing amplitude from left to right, with about 10 or 12 cycles within one horizontal sweep (as you can count by looking at the TV screen). This decaying sine wave will be added on top of whatever normal waveform is at the place you are probing.

Absolutely! As I said above, just try adjusting the vertical height, and you will see the moire' move. There is ALWAYS some moire' in color CRTs. the spacing of the dots or stripes on the CRT face is designed to produce the finest possible moire' pattern with the particular number of scan lines in NTSC or PAL, but it cannot be totally eliminated.

I rotated the yoke a couple of weeks ago to level the image. It was about 1/2" higher on the left side. I don't know if I noticed the moire before that as I was so busy making adjustments. Since an image that isn't centered horizontally drives me crazy, and I just got the convergence where I can live with it, I can't bring myself around to touching the yoke. :)

I have jumpers with alligator clips, would those be good for grounding? I can clip from ground to ground on the modules and then to a good chassis ground.

The scope has a X1, X10 and X100 setting and the probe has X1 and X10. I'm not sure what the maximum is, but I understand this one can handle all the way to the yoke and high voltage.

The scope can either sink with the probe, it's internal (using the AC line, I believe) and an external source (of which I don't have).

Where in the horizontal should I start? Should I start at the HOT and work my way back?

If I turn down the brightness, the screen goes black no matter how high the contrast is set. Because of this, I can't see if the bars are still there. Now if I turn the contrast all the way down and the brightness all the way up, I can see faint bars.

Sorry I have very few Sams. Not to throw more confusion into this, but this is a video that goes over the concept of O'scope bandwidth, and is good for your problem.

http://www.youtube.com/watch?v=oZ1Dv2dVGkU

After the 2:50 point he starts getting into the "ringing" on an otherwise low frequency oscillator, and the bandwidth you will need to find your problem.

This video shows a little about roll off and why your scope should have a bandwidth well above what you actually want to be able to measure. And it all comes down to what makes up a wave form. He does not go into it here, but a square wave of 1khz actually needs a bandwidth multiple times that 1khz to be accurately displayed on an oscilloscope.

http://www.youtube.com/watch?v=pGwL6FadC9U

Your oscillation is about 10X horiz scan rate, easy to see as you have at least 10 visible vertical bars on the screen, As stated, around 200K, so you will need a scope that has a 1mhz bandwidth to see the ringing clearly. The above video explains the roll off of the scope, and why partly the bandwidth should be 1mhz. He is correct in this.

Another person asks if the bars get darker if the contrast knob is turned. With the same white screen, no signal, when turning the contrast knob through its range, does the bars change in their appearance? If not the noise is getting in other than the video amplifier circuit, (power supply because of bad decoupling cap) if they change significantly then the noise is being amplified by the video amplifier. So its a signal level noise.

Regardless of how the noise gets in, its source is likely at some point in the horizontal section. It is possible it can come from your corona source, does it intensify as you do something to cause the field to come close to arcing?

Other than that, there are two attached pictures from a tv I own, its not yours, but it shows parts near the horiz. area that can be culprits of your problem. Suspect any parts near the red dots, resistors, caps, inductors. You should go to the Sams website and buy your tv schematic, look around in the same parts of the tv, Horiz Osc, Driver, and output stages. There are two red arrows on one of the pictures, they point to waveforms that are capable of generating the "ring" because they are a pulse, and are squared. If a part that is designed to filter out overshoot in the pulse rise is bad, then the circuit, or following stage will momentarily oscillate at a higher frequency and give you that ring, and go into another part of the tv and give you those vertical bars...... Do not overlook shielding, of any parts, picture tube, or grounds.

This is a likely description of what could be causing those bars, its your job to look for a bad part in those areas, you will likely need the Sams, and possibly a good scope, and (2) 1mhz - 5mhz 10X to 1X probe with capacitance trimmer built in. There are good, inexpensive 20mhz - 100mhz Tektronix scopes and cheap starter grade probes that can be had for around $100. + Shipping, sometimes less. (Yes go for more than a 1mhz scope) You may need a second probe to connect to a horiz sweep sync source, as stated be another, so you better get two.

I wish TinCanAlley lived closer to me, I'd bring my Tektronix 2236 over to offer assistance.