Admirial 30A1 white vertical stripe
 

Hi All: I just recapped a 1948 Admiral 30A1. After fixing all the typical issues like the horizontal linearity and centering there is one problem I have not figured out.
I get this wide vertical white bar down the left side of the screen with retrace lines in it. Is this a sweep issue or a video issue? Any info would help. I am sure this has come up before as a common problem with this old set. Any help would be appreciated.

Likely some variation of horizontal foldover. First try a different damper tube. Sometimes horizontal drive setting can affect it. The vertical retrace lines are probably a separate issue. I don't think those early Admirals had vertical retrace blanking, and so with high brightness and contrast settings that's a fairly normal thing. Oh and welcome to the forum.

With a picture on screen, turn the horz.hold control both directions (but not so far it loses sync). Does the white bar change/move/shift at all?

Hmm. In the second picture we're seeing the horizontal blanking bar on the right-hand side, which could indicate the whole picture is being scanned but not in perfect sync with the TV's horizontal frequency. That being the case, if he moves the picture to the right with the horizontal control, we may not see any horizontal blanking on the left-hand side? I guess in theory the horizontal blanking bar should be equal width on both right and left sides if the horizontal oscillator is in perfect sync with that of the signal it's receiving?

The horizontal AFC detector (and or hold pot setting) can be off far enough to sync such that active video is present in the retrace creating a foldover look...A worthwhile problem to rule out early.

Check the big power resistor inside the HV cage. They are often bad

Agree. The problem is AFC can be so effective that one can't get the horizontal hold control to shift the picture enough without disabling it. I have my Emerson 698 on the bench, which when wave shape is adjusted correctly, the hold will only budge the picture about an 1/8" in either direction, which is the goal with AFC. The Admiral 30A1 AFC may not be so aggressive.

Thank you all for your input on this strange problem.
I did some experimenting and testing on this problem and this is what I found....
The Damper tube tested good.
The white bar does not shift at all when turning the Horz hold.
The power resistor was bad and had been replaced.

I grounded the video signal at the video amp to eliminate a picture on the screen but kept the sweep circuits working , and the white bar is goes away.

This lead me to believe the problem causing the white bar is in the video signal.
With video input connected again, I traced the problem back from the output of the video amp output tube V307 back to the output of pin 7 of the V305, the 6AL5 video detector output as shown in attached photo.

This video signal can be seen as a higher level after blanking. It seems to be causing the white bar .
I replaced the 6AL5 with another good 6AL5 and there was no change. Could this problem be before the video detector?
With video on the screen, the entire picture is shown. The white bar is superimposed over the picture. I am at a dead end and don't know where to go from here.

[/If you pull the 6AL5, is the white bar still present?

That is an interesting problem. Seems like a delayed version of the horizontal sync is getting into the video. Are you certain you didn't miswire something? Maybe it is coupling to the local B+ supply. How about a schematic.

Here's the horizontal section from Sams. I don't understand why when I link to my Flickr url here on VK it always looks blurry when I click on the link and does not zoom to the same size as when I view it directly on Flickr. Anyone have any idea's why that happens? [edit] I might have found the issue, see if the second link works better for ya.

https://live.staticflickr.com/65535/...a5a6838a_b.jpg

https://www.flickr.com/photos/152661...posted-public/

And here's the flyback end of the Horizontal section.

https://www.flickr.com/photos/152661...posted-public/

How to link a Flickr image so it shows an image of desired size instead of just a URL:

Go to the image (your second link, for example) on Flickr.
Click the Download arrow at lower right and select "View all sizes"
On the "Photo - all sizes" page, select the size you want.
Right click on the image and select "Copy image address"
Back on videokarma, "go advanced" to show all the options for your post.
Click the "Insert Image" icon (looks like a mountain and sun).
A small window pops up. Press Control-V to copy the URL in the box.

https://live.staticflickr.com/65535/...7b99acb5_k.jpg

That is a bit too big...IMO.

I prefer this method for speed/ease of use YMMV. http://videokarma.org/showpost.php?p...&postcount=238

Thanks, but too much information. :D I just wanted to know why the image was blurring out with the link I'd picked. Maybe it's just me, but for viewing a schematic I prefer clicking a url link and then being able to expand and pan around the image rather that have a blown up portion of the image showing directly in the thread. :scratch2:

When I pull the 6AL5 detector, the line goes away. I am sure I have not miswired any caps.
With no video there is no line. If I lower the contrast, the line gets dimmer. If I adjust and increase the contrast it gets brighter at the mid point of the pot as shown in photos, then decreases and shrinks back as I increase contrast as it seems to overdrive the circuit as shown in the photo with thinnest line. This test was done with my signal generator with a cross as shown.

I wonder if this could be horizontal garbage on the contrast control line? Can you see any pulses on the contrast control? Are all caps connected to it good (C7, C6, any others that may be off the edge of the schematic you posted)?

Edit: you could try bridging these points to ground with a spare 50 microfarad.

I have now directly connected video from my generator to C28 which connects to pin 1 of V9 of the 6AU6 video amp. The picture is now clean. The white line is gone. The problem must be in the IF system ahead of the 6AL5. How would you track this problem in the IF stages to locate the problem?

Try AC shorting the grids to ground, through a cap,
going backwards, to see if the IF is near oscillation.

or

just align per instructions.

Though this indeed looks to be more idiosyncratic than
misalignment.

Is the white bar still present with no signal (i.e., just snow)?

Brett: I think you are on to something. It has a flaky contrast set up. I will check it out tonight.

You might try displaying that video line on your scope like in the second picture, triggering on that channel. On a second scope channel probe around to see if you can find a pulse that occurs when the white line does (the jump up in the video trace). That might lead you to where the two signals are combining. Maybe a leaky tube socket.

EDIT: I wonder if it has to do with the DC Restoration circuit.

Doesn't it look like the contrast control in that chassis is basically controlling the gain of the rf and possibly a couple IF tubes, like a manual agc? I think that practice was found to be a no-no pretty early on in the game, and most manufactures opted for controlling the gain of the video amp.

Hm.. since it's manual, wouldn't it be mgc 'stead of agc? Just messin with ya. :D:tongue:

Good catch. :D

More testing.....
If I pull the signal off the antenna input, the white bar goes away. Only snow appears on the tube.
If I tweak the horizontal hold so the picture unlocks horizontally, the white bar stays in place and does not track the horizontal sync bar. See photo.
Again, when a direct video signal is applied after the detector tube to the video amp, the picture looks great and there is no white line.
Bar only appears when video off the detector feeds the video amp.
Since the white bar does not track the horizontal sync pulse, I am now really confused. I originally thought the white bar was part of the picture as it does show up that way on the scope, but looking at the photo I took off the CRT, the picture information is separate from the video image.

This does make sense if you understand that the black bar is always part of the video. The black bar is where the horizontal video sync input pulse is in the video signal. The white bar in your case IS coming from the horizontal sweep signal, it always is at the start of the sweep. Looks to me that part of the horizontal sweep sawtooth signal is getting into the RF-IF-Detector area.
Are there sweep wires (like yoke) near that area?

Exactly. The deflection is is leaking into the tuner or IF stages.

Another thing to look out for is missing shielding on the tuner/IF (especially tube shields) and the HV (is the HV cage installed?). If there are any B+ lines shared between the horizontal stage and the tuner the filtering on those is suspect.... may want to check for heater-cathode shorts in the tuner/IF and the horizontal stage too.

What is the actual signal source you've got going to the antenna input?

For a Signal Source I have used both off air signal from a VHS Deck modulator on Channel 3 and a also a Leader LCG-396 NTSC Pattern Generator.
The HV cage is installed.
Only one tube has a shield and that is the tube at the very front end of the tuner. Does anyone know if this set came with tube shields?
B+ is not used in the IF circuits. Only used in vertical output stage from what I can see on the schematic.
No Yoke wires in this area of the IF strip.

The IF has to be supplied positive voltage from some B+ rail of some type or it wouldn't pass any signal at all...

If the schematic happens to use the archaic B+, B++, B+++ notation to differentiate the different B+ rails know That I wasn't referring to the B+ rail specifically but to all positive supply rails categorically when I used B+ in a previous post (and I generally refer to it categorically in most posts I make). If any positive rail is shared between the tuner/IF and the horizontal sweep/sync separator that could be a leakage path for the noise you see.

Problem Solved!!!!!!
I traced the distorted signal all the way through the IF to the Tuner.
I found that the power to the tuner had the same distorted pulse that the video had.
I traced the tuner power to the power supply chassis. At that point I knew what the problem was.

This set has a separate duel power supply that sits under the main chassis.
One High voltage supply supplies power to almost all of the main chassis for IF, Video, audio, sweep and High voltage circuits. Everything but the tuner!

The second supply supplies power to the audio amp (which is also on this chassis with a socket for a plug in speaker) and also supplies power to the three vacuum tubes on the tuner.

The speaker on this set uses an electromagnetic coil, not a permanent magnet. The coil also acts as a filter for the low power supply. Without this coil plugged in with the speaker that is mounted in the cabinet, the power to the tuner is unfiltered with this pulse that caused the white bar in the video signal.
I really screwed up and forgot about this coil and have been chasing a non problem for over a week. Live and learn.
Thank you all for your help and keeping me going on this crazy problem. I learned a lot from you guys while chasing down the problem . I could not have fixed it without you.

The picture is nice and bright without the white line as long as it is in the cabinet.
I still have some horizontal linearity issues but I can live with that for now.
Thanks again

A good lesson to always connect field coil speakers and any speakers that mount the audio output trans to the speaker frame...Those sets sometimes use the audio stage in place of a B+ voltage dropper and if you remove plate bias from the audio output tube other stages fed dropped B+ by the audio output cathode suddenly have no B+.