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

[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!

[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.