Two Way Hourglass Bends on My KCS47

[Chris K]

Hi all. Have the 6T65 16GP4 RCA working OK (more troubleshooting advice needed for a different issue than this). The picture is slightly bent pinched in a bow shape top and bottom and side to side. Obviously something to do with the yoke. Any ideas on what might be going on?

[Kevin Kuehn]

Edges appeared straight back in this photo, what has changed? Are you sure the yoke is all the way up to the CRT?

[Electronic M]

I suspect the sides are straight in the first picture and the curved mask is tricking the eye. For stuff like this a crosshatch test pattern is a good idea as regular programming content and mask shape can obscure the actual nature of what you're looking at.

[Chris K]

What's different is the yoke. Let me explain. The cockeyed picture is with my restored chassis from the original dark wood TV transplanted to the blonde cabinet and the yoke on the CRT original to the maple set. After an afternoon monkeying around with its original yoke to straighten out the picture without success, I took it off. The set screw wing nut that allows you to rotate the yoke was cross threaded and you couldn't tighten it down and, the yoke didn't look too good. OK I thought, just take the yoke off the dark cabinet set and put it in the maple set so now. the restored chassis is paired to the yoke it powered in the dark TV. The picture in the original TV didn't have this problem so it probably is a positional issue but I don't know how movement in and out along the neck could cause this.

[Kevin Kuehn]

If the yoke is too far back the beam can be obstructed by the aperture of the electron gun. Also the positioning of the Ion trap can have some influence, since it also bends the electron beam. The trap should be adjusted for maximum brightness with the yoke all the way forward against the CRT bell housing.

[Chris K]

Originally Posted by Kevin Kuehn

If the yoke is too far back the beam can be obstructed by the aperture of the electron gun. Also the positioning of the Ion trap can have some influence, since it also bends the electron beam. The trap should be adjusted for maximum brightness with the yoke all the way forward against the CRT bell housing.

Ok I’ll make sure that’s the case. Stand by

[bgadow]

Also makes me think of a low voltage issue. Did anything in that part of the circuit change?

[Kevin Kuehn]

Originally Posted by bgadow

Also makes me think of a low voltage issue. Did anything in that part of the circuit change?

That could be too. In general there seems to be an under scan issue. Ordinarily one should be able to fill the mask plus a little more to keep from seeing the edges during line voltage fluctuations. Chris you may want to consider posting your picture over on the ARF forum. Things seem a little slow around here and their are some really sharp engineering types over there as well.

[old_tv_nut]

Under the principle of "fix the obvious first," the straight edged picture is with one yoke and the curved edge pic is with a different yoke, right?

I would suggest going back to the first yoke to verify that this change is due to the yoke and nothing else. If that's the case, it may be that the yoke that produces curved sides has either a different winding pattern and or metal/magnetic elements that produce the curve and is intended for a different CRT/receiver, on which it would produce straight edges. Or it may be missing some elements that would correct the curved edges.

Can you see any adjustable pieces on either yoke?

[Chris K]

This yoke made a straight edged picture in the original tv in other words, if I had harvested the 16GP4 from the maple set and installed it in my original dark cabinet, as was the plan, it would e the exact same situation. When I got the maple tv with the strong CRT, it had its original yoke and chassis. I took my restored chassis from the original tv and put it in the maple tv but left in the yoke that was in the maple producing the small crooked but straight edged picture. I couldn’t get that yoke to produce a full screen picture so I pulled the yoke from the original tv. This chassis yoke combo produced a dim but straight edged picture in the old set with the weak CRT. I don’t know what could possibly be different other than I didn’t put the yoke in correctly when I did the swap

[Chris K]

Originally Posted by Kevin Kuehn

That could be too. In general there seems to be an under scan issue. Ordinarily one should be able to fill the mask plus a little more to keep from seeing the edges during line voltage fluctuations. Chris you may want to consider posting your picture over on the ARF forum. Things seem a little slow around here and their are some really sharp engineering types over there as well.

I’m going to play with the yoke that’s in it currently and make sure this is a real problem and not some error I made when installing the yoke. The only other thing is Tom mentioned this chassis and the yoke are a bit unique. But I can’t see why that would make a difference. The only things that are different is it’s a stronger CRT and I put in the yoke. This yoke/chassis combo was fine in the old set in terms of deflection…the picture was bad because the CRT is weak. Now that chassis and yoke is in a cabinet with a strong tube so this should work shouldn’t it? If I had swapped the CRTs instead we’d be in the same configuration but in a different cabinet so that’s why I need to make sure the yoke is in there correctly.

[Kevin Kuehn]

Originally Posted by Chris K

. Now that chassis and yoke is in a cabinet with a strong tube so this should work shouldn’t it? If I had swapped the CRTs instead we’d be in the same configuration but in a different cabinet so that’s why I need to make sure the yoke is in there correctly.

All assuming both KCS 47 chassis us the same direct drive yoke part number, which I don't know how they couldn't, but something is obviously different between the two. Any difference between the 2 focus magnets? If I'm not mistake the yoke has an octal plug that connects it to the chassis, so there's no way it can be mis-wired.

[Chris K]

Correct the socket is on the side of the high voltage cage

[Kevin Kuehn]

If you can't get to the bottom of this, I'd suggest repairing the striped adjustment thumb screw treads on the yoke original to that chassis. Then you'll at least have a known baseline to move forward. Things can easily get wonky when you randomly start changing out parts.

[old_tv_nut]

Help me understand - this yoke produced a straight sided image with the same CRT type number or different? With the same focus coil and CRT accessories, or different?

Making a straight raster curve like that is not a minor difference, you should be able to find it.