Can't find my book!

[radio nut]

I have one of the books that helps you diagnose a tv by the issues on the screen , like foldover.
Well, I just moved and can't find it...
OK, that leaves me two questions.
First I have a set that has both dark and bright (compared to the rest of the picture) lines on the left side of the screen that start at the top and work their way down but not all the way down the screen. they are just darker or brighter than the rest of the image. My phone just does not want to get a clear image of it or else I would post it.
Any ideas? I did put a new yoke in this set and removed the caps in it because it's directions stated to install exactly like the original. I am not sure if this is a cross talk issue but it seems to have kinda just started and seems to be slowly going farther across the screen.

Second, I remember reading about ( I believe) inter element capacitance in the crt itself that required a neutralizing cap to be installed between the grids(?) under the chassis.
Anyone know about this issue?
On my set I did tip it over on it's side when it was running so I could check voltages and after that I did lose the picture. Since then I had to put the ion trap on the other side of the crt neck and it will not show a picture with the trap on the original side.

[ChrisW6ATV]

This is not my area of expertise, so I cannot help. You may get more responses if you can change the title to something like "Yoke problem on RCA 16-inch model xxx" or similar, I would think.

[earlyfilm]

The first problem, is you don't say what era TV you have, or make and model and that prevents anyone from giving you specific instructions.

The left side picture defect sounds like Barkhausen. I say "sounds like," because a picture surely would help to confirm this. There also is a pretty good chance that you will invent a new cuss word before you find the cause!

The cause of this defect is electromagnetic radiation (or rarely electrostatic radiation) from the horizontal sweep that is being picked up somewhere between the antenna and video signal to the picture tube. Since there is a time delay here while traveling though the circuits the second time, the spike or spikes are shifted into the picture.

The below is general procedure for 1940 to mid-1950s electromagnetically deflected TV sets:

The usual cause for this is any tuner, IF or video tube that is missing its shield, or the shield is not properly grounded.

Or, the antenna lead is not shielded or possibly dressed too close to the horizontal output tube, the flyback or HV lead.

Or, if the antenna input is coax and the center and ground connections are reversed, as with a balun coil connected wrong. (This problem usually will come and go as the cable is moved.)

Or, the HV cage is missing or not properly grounded.

Or, aquadag coating is not grounded.

Or, HV lead not fully seated in the CRT.

Or, a current limiting resister in the HV lead is breaking down.

A remote possibility is lack filtration in the control circuit if your set has AGC keying.

On string filament-chassis, a heater cathode short can cause this.

Usually not, but I've seen gassy or slightly shorted tubes cause this. When all else fails, substitute one-by-one all tuner, video IF, AGC, and video amplifier tubes.

Now here is the kicker! Sometimes it goes away for no apparent reason, and only reappears when you clean up and put everything back together!


The second defect, having to move your ion trap, sounds like something such as the CRT, the yoke assembly or the focus assembly or focus coil shifted when you tipped the set.

Your two defects probably are not electrically related. (An exception to this might be if the current limiting resistor in the HV lead is failing.)


James.

[radio nut]

thank you for your response. this problem is once again my 1949 muntz set. to be honest this set seems like a lemon and has been one problem after another. just pure frustration. i will check the things you mentioned. I just want to be done working on this set!

[Phil Nelson]

Originally Posted by earlyfilm

The left side picture defect sounds like Barkhausen.

I had one set (a Hallicrafters T-67) with a textbook case of Barkhausen oscillation. It made a squiggly vertical line in the left portion of the screen, which was otherwise normal:



The cure, which is the first one recommended in my old TV books, was to substitute the horizontal output tube.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

[radio nut]

thank you! I really do not like posting new questions about the same set over and over, makes me feel like like a forum hog!.
tell you what though, this set has been a real teacher since with help from this forum i have had to figure out a multitude of issues!

[earlyfilm]

Originally Posted by radio nut

thank you! I really do not like posting new questions about the same set over and over, makes me feel like like a forum hog!.
tell you what though, this set has been a real teacher since with help from this forum i have had to figure out a multitude of issues!

Radio nut,

If you had added this symptom to one of your previous posts, that might have informed the rest of the forum what general vintage set you were working on and what you had done previously.

As for Phil's tube substitution suggestion, yes, that is the thing most books suggest because it is the easiest thing to do. With that said, I've found that it usually is not the problem if one has done the standard visual inspection of an improperly working set.

This would include visually inspecting the horizontal output under reduced lighting for either a pink glow on the plates, or a purple glow shining out from inside the plates. If so, replace the tube. If the problem seen was pink plates, immediately check the difference in the grid voltage and cathode voltage to determine why the old tube overheated from pulling too much current or you will fry the new one in short order.

(Tubes with a purple glow may be used as long as they work properly without causing a problem, when confirmed by substitution. Sometimes, if you catch the pink plate issue quickly enough and the cause is a fixable under the chassis component, the overheating tube may be salvaged, too.)

It is very rare to find Barkhousen caused by a horizontal output tube that is not showing these symptoms.

The pink plate problem can happen to any tube, and should be the first thing you do at your first power up of the recapped set! It is as basic as smelling for overheated parts. The most common in 40's & 50's tubes suspected of having this problem, in order of probability, are Rectifier, Damper, Horizontal Output, and Audio Output.

James

[Zenith26kc20]

If I remember from a long time age, putting an ion trap around the horizontal output could stop barkhausen also.

[radio nut]

Well, I tried taking pics again, and with my phone I cant get a real good image but I will kep trying. I subbed in The Hot ,and high voltage rectifier and had to readjust horiz. hold but noticed a cleaner picture. found a nos damper put it in and now the problem is changed a little. There is about a 1 to 1.5 inch darker than the rest of the picture bar on the left and everything in it is fuzzy and magnified. when a person walks across the screen their shape changes. I will see about putting the original damper tube back in and see what happens and borrow a digital camera for pictures.
I did make sure that the high voltage lead to the crt was tight and the ground to aquadag finger was snug on the crt also

[earlyfilm]

Originally Posted by radio nut

Well, I tried taking pics again, and with my phone I cant get a real good image but I will kep trying. I subbed in The Hot ,and high voltage rectifier and had to readjust horiz. hold but noticed a cleaner picture. found a nos damper put it in and now the problem is changed a little.
There is about a 1 to 1.5 inch darker than the rest of the picture bar on the left and everything in it is fuzzy and magnified. when a person walks across the screen their shape changes. I will see about putting the original damper tube back in and see what happens and borrow a digital camera for pictures.

Radio Nut,

Did your original symptom look like Phils' very clear photo above?

In it, there is no shading, just two vertical lines.
There is no image fold or magnification (stretch).
The left side vertical lines may be speckled or they may be black or they may be white or a mixture of the three.

If not, you did not have Barkhausen!

This tube switch reduced the Barhausen, but created a new problem that I underlined in your reply. Correct?

On your circa 1950 Muntz, you have four controls grouped together on the right side of the back of your chassis. The bottom left of those four is the Horizontal Drive trim capacitor . (One side of the trim capacitor is grounded and the other connects to a 100 ohm resistor going to pin 5 of the 6BG6, a 470K resistor going to the ground and a small capacitor going to horizontal oscillator transformer.)

Did you turn this trimmer capacitor before the fold problem appeared? If this not the same problem you had before the tube swap, try adjusting the trimmer with the new tubes in place.

A single horizontal fold is usually horizontal drive, that adjustment. The fold may be on the left, but more often is near the center of the screen.

Adjust the trimmer for least fold (and best linearity), while measuring the voltage ground to cathode on the 6BG6. You want that adjustment to be on the side of the range where there is the least voltage on the cathode (in other words, with the tube drawing the least plate current.) The need for readjustment is not unusual when replacing the Horiz Output tube.

There may be other causes, but an incorrect drive setting is the most common.

James

[radio nut]

Mine IS shading and image distortion, but I just realized what " might" be the cause.
In the high voltage cage is a chassis mount resistor that went bad. I installed a high wattage brown resistor in there and it is just kind of sitting right next to the damper tube. It can be bolted to the chassis but since there is not a hole in the metal near by I did try to solder it to one of the old chassis mount resistor pins but the solder will just not take to it.
the end result is it is very close to the damper tube. I thought about putting it under the chassis but do to its heat I figured it would be better left in the high voltage cage. If I can get some sleep I will move it around and see if it helps or makes the problem worse. The horizontal hold is what needed adjustment after tube swap.
I did readjust the horiz. drive and it does affect the picture but not this issue.
From an earlier post I noted that I had lost the shut off dot, since the tube swap it is back.

[radio nut]

Lets see if this pic helps!

[radio nut]

The real bright line running at an angle is just from the phone.
Above the quilt square on the left you can see a dark line and on either side it is brighter. The wide darker line from my earlier comment went away once I pushed the resistor over a little farther from the damper tube and pushed extra wire back under the chassis.
I am now wondering how sensitive the damper tube is to items near it.

[old_coot88]

For the heck of it, i would try putting the components back in the yoke that came with it.

[earlyfilm]

Originally Posted by radio nut

. . . . . . I did put a new yoke in this set and removed the caps in it because it's directions stated to install exactly like the original. . . . . .

The factory schematic for the Muntz 17A2 (Rectangular 16 inch CRT) shows no capacitors in the vertical yoke, but one 56 pf across the horizontal winding that is between the center connection and the Flyback.

Why did you replace the yoke?

If the yoke was shorted when you got the set, there is a possibility that the previous service person trimmed the capititor out, to confirm that the yoke was bad and not the capacitor. Doing that was SOP back in the day before the shop plunked money down for a new yoke. They were not returnable if installed. Most people junked an older set rather than pay what a new yoke installed would cost.

The vertical squiggle (vertical ringing) in the horizontal lines on the left edge indicates cross talk from some to be determined source, the yoke is one possibility, and another are the electrolytic capacitors. You did replace them, didn't you?

I am agreeing with Old Coot here the cap in the yoke.

Also, redress the position of the resistor and leads to as near where the old one was. When you have drilled out the old one, use one of the holes to mount the new one. (Don't to this and the capacitor test at the same time, or you won't know which worked. It makes no difference which you do first, but leave the first in while you do the second.)

James