My Christmas day 9T246 restoration! Almost.....

[Kamakiri]

Another interesting thing has cropped up as well. Watched the set for a bit, and I noticed that after about 15 minutes, the horizontal sweep shrunk about 1/2" on each side. The picture itself didn't seem to compress, the sweep just shrunk. It didn't shrink beyond that, but the picture did seem to dim somewhat. I can bring the picture back to the edges with the AGC, but then it goes out of focus. If I tune the set to a blank channel, it gives a full raster.....

The 6BG6 was very slightly gassy, and now it seems to be more so. Didn't check the tube yet, but I have a spare that I'm going to plunk in to see if that changes anything....

[earlyfilm]

Originally Posted by Kamakiri

"HORIZONTAL LINEARITY". Well son of a gun!

Powered up the set, and went to adjust it when I realized that the adjusting screw that would be IN the pot, is missing!

Kamakiri,

Lets determine what happened. The Horizontal Linearity in this set is a coil and not a pot. I assume that your typing got a little ahead of your thinking.


On the apparently missing slug in horizontal linearity coil, find another slug from a junk chassis about the diameter as the hole in the present coil and try it. It probably won't be correct, but it will be a lot closer than no slug. After finding a slug and adjusting it for more or less correct horizontal linearity, repeat the horizontal alignment instructions in the sequence that RCA and Sams gives them.

http://www.earlytelevision.org/pdf/R...-Sams-74-8.pdf

Sams page is 18, the PDF page is 21 for the alignment instructions.

Make a paper print of the page and check off each as you do it.

You will notice that Horizontal Linearity adjustment is in the 8th line of those instructions.

Misadjustemnts here could cause the shrinking that you mentioned in your next post, and so could an incorrect horiz drive setting, or a cathode resistor heating.

Consider finding a 1950's or early 60's era scope. They are not expensive. After a simple recapping, they will be as good as new. Be sure to pick one where the schematic and service instructions are available. The newer scopes are more expensive and they are not as rugged when used around tube era voltages. After you have a scope working, see how far you are out on the "peaks" that you assumed were perfect.

James.

[Kamakiri]

Yes, I'd meant to say "coil", thanks for the correction

I've got a Hickok scope that would fit the bill, just needing a recap....something that I've been meaning to do.....actually was going to be my next project after this one.

Just so I'm following correctly, a misadjustment in this would potentially cause cathode resistor heating......is it likely that the resistors that were weak to begin with? I'm assuming the heating would cause failure, if the set were operated long enough, and the heating is being caused by an overload.

You'll need a little patience with me at this stage, as I'm trying to understand what is happening, electrically.

[earlyfilm]

Originally Posted by Kamakiri

Just so I'm following correctly, a misadjustment in this would potentially cause cathode resistor heating......is it likely that the resistors that were weak to begin with? I'm assuming the heating would cause failure, if the set were operated long enough, and the heating is being caused by an overload.

Arrrrgghh! No. I was talking about sweep shrinkage that could be caused by misadjustment. This would be the result of the problem and not the cause.


I was also typing without thinking and changed subject in mid-sentence.



My one sentence expanded and written as three sentences:

Misadjustments in the syncro-guide circuit (page 18 above) could cause the sweep shrinking that you mentioned in your next post.

Other causes for this shrinking might be an incorrect horiz drive setting (the trim-cap), or a cathode resistor heating or one of the low voltage electrolytics in the horiz sweep. In short, anything in the horizontal sweep and sync circuits that causes a tube to pull too much current or simply a gassy tube can cause sweep shrinkage.

(Reasoning: Normally when a picture blooms, as you described, one assumes that it is a weak 1B3 or an isolating resister in the HV circuit. However, you mentioned that the image seems to be cropping while shrinking. This latter clue may or may not indicate a sync issue, especially the timing and/or pulse width, in the circuit where the horiz sync pulse is feed back to the sync tube, or simply a syncro-guide misadjustment.)
_______________________________________________

On your Hickok scope, make sure you either have the original probes, or the circuit diagrams of the original probes, so you can repair or make new ones, as they are a needed part of the scope. A set of correct probes is needed not only for use, but for the safety of your scope.

My suggestion for now is for you to go ahead and set the TV by eye. After you have repaired your scope, you recheck the sweep and set the peaks and then recheck the whole process. My guess if that you will find it works better after being scoped. These controls do interact and can sometimes confuse an experienced repairman.

For the record: During the era that these sets were in use, one would sometimes find the linearity coil slug or both the slug and brass screw missing!

[Bill Cahill]

Horizontal linearity has nothing to do with locking the picture. It is meant to make the picture physically more linear.. That is Not squeezed, stretched, or, oblong. It has nothing to do with the oscilator. That control is an adjustable capacitor. Looks like someone lost the screw. Hope they didn't als lose the sheet mica.
Bill Cahill

[Geist]

Hi All;
I am truely again amazed at the Knowledge and Insight of a number of the People in this forum..
As I have said in many other groups that I belong to, that the Knowledgeable people in the group should write a Paper or Book, so the knowledge can be passed on to those of us who are either too young or who have just gotten into that particular hobby. And so the experience and knowledge will not be lost, atfer they are gone..
It is a real education to save and print out this and many other postings that really get into the meat of a particular problem.. Thank You to those who help in the education of the rest of us..
THANK YOU Marty

[Kamakiri]

Originally Posted by earlyfilm

Arrrrgghh! No. I was talking about sweep shrinkage that could be caused by misadjustment. This would be the result of the problem and not the cause.


I was also typing without thinking and changed subject in mid-sentence.



My one sentence expanded and written as three sentences:

Misadjustments in the syncro-guide circuit (page 18 above) could cause the sweep shrinking that you mentioned in your next post.

Other causes for this shrinking might be an incorrect horiz drive setting (the trim-cap), or a cathode resistor heating or one of the low voltage electrolytics in the horiz sweep. In short, anything in the horizontal sweep and sync circuits that causes a tube to pull too much current or simply a gassy tube can cause sweep shrinkage.

(Reasoning: Normally when a picture blooms, as you described, one assumes that it is a weak 1B3 or an isolating resister in the HV circuit. However, you mentioned that the image seems to be cropping while shrinking. This latter clue may or may not indicate a sync issue, especially the timing and/or pulse width, in the circuit where the horiz sync pulse is feed back to the sync tube, or simply a syncro-guide misadjustment.)
_______________________________________________

On your Hickok scope, make sure you either have the original probes, or the circuit diagrams of the original probes, so you can repair or make new ones, as they are a needed part of the scope. A set of correct probes is needed not only for use, but for the safety of your scope.

My suggestion for now is for you to go ahead and set the TV by eye. After you have repaired your scope, you recheck the sweep and set the peaks and then recheck the whole process. My guess if that you will find it works better after being scoped. These controls do interact and can sometimes confuse an experienced repairman.

For the record: During the era that these sets were in use, one would sometimes find the linearity coil slug or both the slug and brass screw missing!

I get where you're going here. I was going to ask, then why does the set have a full raster on blank channels, but as I'm understanding this, there wouldn't be, because there is no signal for the syncro-guide circuit to do anything *with*. Since there is a full raster off-channel, I'm not dealing with a deflection or HV issue, that would be the wrong circuit to even think about. Am I on track here?

Being responsible, the first thing I have to do is re-check all of the tubes in that section (might as well re-check them all).

Should I do any further component checks (as in resistors, etc), before I begin eyeballing the setup? The set has about 8 hours run time on it since the re-cap, I just don't want to let any "bugs" it may have do any damage.

[earlyfilm]

Originally Posted by Kamakiri

I get where you're going here. I was going to ask, then why does the set have a full raster on blank channels, but as I'm understanding this, there wouldn't be, because there is no signal for the syncro-guide circuit to do anything *with*. Since there is a full raster off-channel, I'm not dealing with a deflection or HV issue, that would be the wrong circuit to even think about. Am I on track here?

Yes! And also why adjusting your AGC shifted this!

Many newbies mistake this for image bloom from high voltage issues and it is kinda hard to locate the trouble when looking in the wrong place.

Originally Posted by Kamakiri

Should I do any further component checks (as in resistors, etc), before I begin eyeballing the setup? The set has about 8 hours run time on it since the re-cap, I just don't want to let any "bugs" it may have do any damage.

As you just said, check all your tubes, but remember, the final check on a tube without any shorts is how well it works in the circuit. Actually, I usually check tubes, especially for shorts, before the first power-up, to lessen chances of frying a newly installed part.

This would be a good flow plan to complete the electrical work:

1) Check the 39 & 47 ohm resistors from the cathode of the 6BG6 to the -120v source.

(Not related to the problem at the moment, but also check to see if the fuse in the damper circuit is the correct value. I've seen some of these increased in value by servicemen to prevent callbacks as the sets got older.)

2) Find a slug that fits the horizontal linearity coil and then adjust the horizontal linearity. (Sams # L42 and Adjustment B4) Use your DVD alignment pattern for this. If your linearity does not change, your coil may be shorted, or there may be a wiring error from recapping. The set should be in its working position (not on the side) when making the final linearity adjustment.

If you think the used core you are testing makes too much change, try a smaller core.

3) At this point get yourself a red grease pencil and mark the Sams "B" numbers on the correct parts, so you won't accidentally align the wrong part. (Don't ask me how I know this is important. )

4) If the image looks reasonably OK and only a minimum of overscan, follow the Sams page 7 for setting the AGC Threshold, but do it visually for cleanest picture (ie, back off to just before overload) for now.

5) Follow the Sams page 18 synchro-guide instructions in order, except for checking the waveform. Since you have no scope, yet, you will judge the correct position of B6 by the most stable lock-in range.

6) After finishing step 5, set the set aside for now. If it is behaving better, it is OK to temporarily slide it in the cabinet watch it, since a little running time might help to drive out any remaining moisture.

7) When you get the scope working and you have either built a low capacity probe or confirmed that yours is not leaking, check the B6 adjustment again and if it is out, correct, and let us know what you found.

After correcting the wave form, you probably will have to re-tweak some of the other adjustments.

James.

[Kamakiri]

Tube test done. Geez, found more bad ones than I'd suspected. None that were "toast", but a few that were very weak. Since the set powered up on a variac when I got it to a full raster, and worked after I replaced a few capacitors, I worked the whole thing backwards and never did a complete test of the tubes till now. Dummy.

Replaced the 6BG6, and one 6SN7, listed as "Sync amp - 2nd sync sep". The 5U4 was nearly shot, and the 6AV6 tested as very marginal in one of the three tests.

Going to order some tubes, as I'm out of 5U4s and 6AV6s....on to the resistors.

[Kamakiri]

After some more investigation, I encountered a newbie mistake. It seems that I didn't get the bumblebees on the first time around

Replacing the bumblebee cap on the horizontal linearity coil did the trick. It now locks in solidly when changing the channel.

Also replaced one of the two damper filter caps. The other, as it turns out, I have to order, as I must have used it for something else.

After the capacitor replacement, here's what changed....

Now, though it locks in solidly, I cannot change the horizontal hold at ALL. Nothing seems to affect it. It does lock in properly, but crank the horizontal hold to both detents, and you get no change. Same with the horizontal range control.

It also seems that I'm now getting a buzz in the audio. I can tune it out for the most part, but it's still there. At the beginning of this, I aligned the audio by ear, and got it perfect. Wonder if something is now off, now that I'm replacing components.

The high voltage is low also, as I'm getting blooming with the brightness control, and on screens that would have a very bright picture, such as all white...it goes out of focus. Still some screen shrinkage, but now only on the right side of the picture, and now the screen shrinkage is apparent off channel somewhat as well.

Now the one thing that I DID notice is that if I'm reading this correctly, some TV repairman stuck a .01 bumbebee in instead of a .05 at C91 in the sams, which is the other damper filter cap. Is this a possible cause of this stuff?

I realize that I'm not exactly following the suggestions, but as light bulbs light and I get the time, I've been working on the set with the parts I've got. I'm just going to order the cathode 6BG6 resistors on the next parts order, as it seems that I've got more work to do.....

[Kamakiri]

Yep. In fact, now, if I crank the brightness, the whole picture will disappear.....

[Bill Cahill]

Tim, I'd have to see what you mean by picture dissappears, but, on horiz. hold control having no affect, congradulations. That's how the synchro lock works!
Bill Cahill

[Kamakiri]

Okay, "picture" it this way

The picture is expanding and defocusing as the brightness control is turned up. After the set has been playing for say 15 minutes or so, if I crank the brightness all the way up, the picture gets very dim, and just goes dark. I can get the picture to come back to a dim light by turning the brightness down, and I can get it back to its previous level by turning the brightness ALL the way down, then bringing it back up.

From my reading, this seems to be caused by insufficient high voltage, that the pulse from the horizontal output tube is too low, or the HV rectifier is weak or dead (which isn't the case).

I do know that this issue is worsening progressively as I replace capacitors and tubes, leading me to believe that it's the whole "weakest link" thing, and that it's all coming down to replacement of one stupid component. Once I nail that one component, I think everything will work perfectly.

If that's the way synchro lock works, well then, dammit, mine is perfect

[Kamakiri]

Just discovered that the link above is the wrong schematic. Mine is a later production 9T246, and uses a 6W4 damper, and not a 5V4.

Sort of explains a few things. Time to go sort that out....

[Kamakiri]

By the way, many thanks to Bill Cahill, for pointing out the above