Mighty Monarch of The Air

[old_coot88]

Just curious- is the fine tuning actually working? Do you see a change in the display when you adjust it? If not, the F.T. mechanism might be busted.

[vts1134]

The tuner is a turret style tuner. I did remove it once before and cleaned each (bump?) with contact cleaner sprayed onto, and then applied with, a Q-tip. I also used cleaned the contacts in the set the same way. Is there anything inside the turret that would benefit disassembled it and cleaned it with a similar method?
The fine tuning does affect the picture. It's kind of hard to describe but it's almost like there is two pictures one on top of the other. The "top" picture has some wavy lines that go from the top of the screen to the bottom. Then there is the "bottom" picture which is the signal from the VCR. The bottom picture as well as the sound are affected by fine tuning. The sound gets quieter and a bit distorted, and the "bottom" picture gets softer at one end of the fine tuning rotation. The sound gets louder and more crisp and the picture gets sharper at the other end of the ft rotation. I don't think the change in picture would show up in a video as it's pretty tough to see with my own eyes.
I'm going to take a second look at all of the connections (and values) of things in the vertical section to see if I can't find something jumping out at me that might explain the problem towards the top of the screen tonight. If the tuner could benefit from an internal cleaning I'll try to get that done as well. My friend at work gave me a can of Tun-O-Wash so I'll can give that a shot.

[old_coot88]

Sounds like the fine tuning is working OK. And it's a turret type tuner. And you've probably done an adequate job on the contacts already.

Before you do any more washing, eyeball the front of the tuner for an access hole to the tuner's oscillator adjustment (sometimes called the 'bulls eye' adjustment). Each of the channel strips contains a metal slug which aligns with the hole when clicked to the corresponding channel (eg., when you click to Ch.3, the Ch.3 slug will align with the hole), and you adjust the slug with a non-metalic thin screwdriver to tune in the channel. Do this with the fine tuning at mid range. (Or if the VCR uses Ch.4, do the same with the tuner clicked to Ch.4).

Occasionally one or more of the slugs will be missing due to someone's screwing them all the way out. You should be able to shine a light through the access hole to verify each slug as present, or pop each of the strips outa the turret to visually inspect them and see if any slugs are missing.

Don't worry about the vertical issue until you get the signal tuned in properly.

[vts1134]

Originally Posted by old_coot88

Sounds like the fine tuning is working OK. And it's a turret type tuner. And you've probably done an adequate job on the contacts already.

Before you do any more washing, eyeball the front of the tuner for an access hole to the tuner's oscillator adjustment (sometimes called the 'bulls eye' adjustment). Each of the channel strips contains a metal slug which aligns with the hole when clicked to the corresponding channel (eg., when you click to Ch.3, the Ch.3 slug will align with the hole), and you adjust the slug with a non-metalic thin screwdriver to tune in the channel. Do this with the fine tuning at mid range. (Or if the VCR uses Ch.4, do the same with the tuner clicked to Ch.4).

Occasionally one or more of the slugs will be missing due to someone's screwing them all the way out. You should be able to shine a light through the access hole to verify each slug as present, or pop each of the strips outa the turret to visually inspect them and see if any slugs are missing.

Don't worry about the vertical issue until you get the signal tuned in properly.

Sadly this didn't do the trick. Adjusting this tuning slug gave me much the same results that adjusting the ft gave me, except on a much bigger scale. Again the "bottom" picture went from sharp to soft to just static on each direction of the rotation, but all the while seemed to be beneath another picture. The "top" picture had no change at all with either the tuner slug, or the fine tuning adjustment. I will try to take video tomorrow while adjusting ft and the tuning slug to show on video what I am describing.

[old_coot88]

Well tarnation. Ain't that a kick in the wazoo. From your description it begins to sound like signal overload, like maybe the set's rather primitive AGC (automatic gain control) system is being swamped. What happens if you loose-couple the VCR's signal going into the tuner? That is, just hang the end of the VCR cable close to the leadin without directly connecting it, to reduce the signal strength.

[vts1134]

I did this test using the signal generator and the rf output of a vcr. I'll show you pictures of the signal generator because it is much easier to photograph the phenomenon I have tried to describe.

The picture above is with the generator directly coupled to the rf input on channel 6. The pattern is vertical lines. You can see that the vertical lines make up what I was calling the "bottom" picture. The three horizontal lines along with the bigger bright vertical line make up the "top" picture. Feeding the signal with the generator makes the bright vertical white line stationary and straight, thereby easier to see. You can see that there is also retrace lines through the picture but that is another fight for another day.

The second picture is with the output of the generator decoupled from the antenna input but still near the input terminals. You can see the signal go down and a bit of static starts to appear. The bright white vertical line starts to curve and make an S pattern. The line has this shape and sways when the set has a moving video signal.

The last image is with the lead from the generator decoupled and out of close proximity to the set.

[old_coot88]

OK, the large disparity between bottom and top should be fixable with the vert. linearity control. Since the lin. and height adjustments are interactive, you'll probably need to juggle both of them several times to get the sweep linear with a bit of overscan at the top and bottom. The vert. hold will probably need resetting as you adjust lin. and height.
The screwiness of the display itself doesn't appear to be from overloading, since reducing signal strength doesn't cure it. It almost looks like the video is negative (phase-inverted). The diode M4 couldn't have gotten connected backwards, could it? The banded (cathode) end should connect to the last IF transformer (L9), and the unbanded end to the junction of coils L10 and L11. The photo you posted earlier shows it connected correctly, so i dunno how it coulda gotten reversed.

Maybe you could post another vid with the VCR, with the signal loose-coupled and the vertical adjustments having been made.