'50 RCA KCS-47A Question
 

I've got 4 or 5 shaded bands down the left side of my picture. Always there but best seen with signal. What is the cause and how do I get rid of them? CRT is a 16bp4 tests good.
Tnx
Terry

I dunno, but in your picture, the CRT looks very dim...

I don't know either, I have a couple sets that do this to one degree or another.
From what I've read I believe the problem in in the damper circuit somewhere.

Assuming you've already recapped this set?

If you have a Horizontal Drive control, try backing it off a bit.

If the drive has no effect and the damper is good, the yoke is usually to blame. You probably have an open or shorted capacitor in the yoke.

I think the technical name for this symptom is ringing. If i can find my service notes I may have some troubleshooting points for you to look at.

I dunno either,but YOUR PICTURE looks very dim...Could you take another a little brighter? I'm wondering if you are talking about Hum bars caused by a bad cap in the horizontal/damper circuits.

Someone mentioned a cap in the yoke. Thats a new one on me.:scratch2: I knew that there were a few resistors in a lot of yokes but wasnt aware of caps. Admittedly I have only popped the cover off of a few...

Yeah the picture is very dark, but that screen should be much more visible. If he had to make the room that dark just so we could see anything on the screen, his CRT is probably very tired...

I think the dark picture is just the camera. It's good in daylight and easy to watch. The set has been recapped and some resistors have been replaced. I did adjust both slugs (top and bottom) on the horiz. osc transformer to bring the horiz. frequencey in to range when I first got it working. I don't know if there is a balance between those two adjustment? I set the top slug in the middle and adjusted the bottom till the picture would lock in. I'll sniff around the damper and see if I can find anything thing.
Tnx
Terry

Those pics are a bit better.

Hm, do the lines change at all? Do they look the same regardless of whether or not there's a signal? In both of your pics, the lines themselves look the same regardles of what picture is on the screen.

I'm pretty sure its a yoke network problem.

Terry: THe transformer can has two functions, phase and oscillator frequency. THe part of the transformer that's available to adjust on the back panel is the secondary of the transformer. It controls the oscillator frequency (horizontal hold) The primary of the transformer that adjusts from the under side of or underneath the chassis is for the horizontal phasing.

Usually the generic way to adjust it (the sams will tell you) is to pull the hoirz afc tube and adjust the oscillator so that instead of tearing the lines stand upright. Then you adjust the phase so that you can make the picture stand still as possible. When the tube goes back in everything should lock into place.

However, being that your picture looks good apart from the ringing I would leave it be.

I'll go with Jordan's idea, but if correct, the Horizontal Drive control should make changes you can see in those bars (make them worse and better.) That could then be one of the small disc caps in the rear of the yoke (if that set has them), or other horizontal sweep issues. But it isn't a bad yoke, if I had my guess at it.

If it's not changed in appearance by moving the drive control, then I'd go with a leaky cap someplace, particularly in the video circuit. If that's it, you should see the bars as a foreign waveform if you scope the B+ to the video circuits.

Charles

The bars don't change just easier to see with no video. There's some disortion in the picture as it pass the bars. This set use a trimmer cap to adjust the drive. I'll give that a shot.
Terry

I'm kinda wondering if the bars are a defect in the glass of the picture tube...

Or did the bars just appear there one day?

Pretty sure they have been there since I started on this project
Terry

Hey Terry, is there a lengthening or shortening of the image where the bars are? If this is a sweep-waveform problem, it would explain why the tube is darker in places, since a faster trace would cause less electrons to hit the phosphor, and would thus appear darker. My Fairfield had some minor distortion on the left side, but it didn't produce those dark bars.

Did you replace that nasty .01 cap across the H-waveform coil terminals? I can't remember if it was you or someone else who brought the subject up a while back. Anyway, my money is on the waveform adjustment slug in the H-osc can, don't remember for sure, but I think it's the bottom one...

Yup replaced the four 1000v jobs over by the damper and yoke socket. I won't get a chance to tinker till Monday but I've got lots of advice to try. I did check the brightness and it is the camera. The last pictures were in a fully lit room and the channel dial lite was on. You can't even see it in the pic. Stupid camera.
Tnx guys!
Terry

If you have a spare damper tube, swap it and look for changes. Rock the tube in the socket, maybe you've got a dirty contact there. I don't have your schematic, but typically you'll have a pair of .05uF capacitors straddling the horizontal linearity control. The 3 components are are collectively called the "boost network". The coil could be bad (unlikely) or the caps could be bad (more likely). If you've already replaced the caps, and you feel confident that they were good to begin with, doublecheck your solder joints and make sure the leads are short and proper.

My TV Consultant 1955 Edition lists this as a "Barkhausen" oscillation. The cause is listed as "interference due to oscillations set up in the horizontal output tube and picked up by the tuner".

Possible fixes are interesting. One is listed as of course swapping tubes but the instuctions go on to say to try a specially designed anti-Barkhausen tube made by several tube manufacturers. I've never heard of these tubes. Also it says to reduce horizontal drive and check linearity adjustment.

Heres another neat idea. Probably the most interesting. Fasten a magnet such as an ion trap to the horizontal output tube and move it around until the line goes away.

Maybe my old book will help you! I hope so. The only other possibility I saw was yoke ringing which someone else mentioned.

Barkhausen lines are much narrower and are usually a thin dark line instead of waves.

I found this illustration of Barkhausen:
http://books.google.com/books?id=ttB...G7PI#PPA225,M1

Barkhausen lines don't affect the sweep linearity either. Jordan has a genuine Barkhausen line here:

http://www.audiokarma.org/forums/att...7&d=1197273277

down the woman's right (stage-left) ear, down her jacket collar and between the 5 and 7 of the 576 phone exchange. It's very minor in his case so I didn't mention it, and it's not present in his other photos of the same set. As you can see, there's no squeezing or stretching of horizontal sweep around that line. Like Eric said, they're usually dark and thin. They also change with fine tuning and are more visible on weaker stations.

Damper failure lines don't change with tuning or signal strength, and affect linearity of the horizontal sweep. Keep looking around the damper-network circuit.

I have another question. The two caps across the horiz linearity coil, are the values critical? Not on this set but others I've worked use a .035 cap which seems to be an odd value. Would a different cause a linearity issue? Like a .03 or .04 rather than the .035? Can a coil be bad if it isn't open? I'm thinking of my Admiral 20A1.
Terry

Ringing is usually caused by a mismatch. Note that the horizontal output transformer and yoke are in series, unlike most arrangements of the era. The lin coil, flyback and yoke must all match. Universal replacements for the flyback, yoke and lin coil rarely worked. Make sure you have RCA originals. The lin coil and surrounding components are critical. I discourage substitutes. When the lin coil is adjusted correctly, the width is at max and horizontal output tube current at minimum. That lin coil will have more effect than in conventional configurations.

If it has a green Merit HOT, you have probably found the problem.

Make sure the 500 mmf high voltage filter cap is OK.

Don

Not trying to argue the point of Barkhausen lines but the books description of the video effect of this are as follows:

"Vertical dark faint line or lines on left side, followed by light area". I picked this out of the guide because it was closer to what I saw in the picture on this thread than the ringing symtoms/illustration. Actually I have never had trouble with either of these things. Just relaying information. Dont get me wrong, debate is great. All of our pool of knowledge here is an amazingly great thing. We are lucky to have AudioKarma!