admiral 24c15 with 20b1 chassis attempt at restore

[bandersen]

Resistors being out by 5 or 10% is not the source of your problem. They could be out by 25% or more and not cause this problem.

It is the horizontal deflection circuit and the magnetic fields.

Make sure you have adjusted the spring loaded mounting screws for the focus coil correctly. That is how you center the image.
Make sure the yoke is seated up tightly against the CRT.
Make sure the CRT is centered in the mounting.
Make sure the ion trap magnet is in the correct spot - it will interact with the focus coil.

When you move the trap magnet around, the whole image should shift and possible distort in the corners. Same goes for the focus coil.

[fumplet]

Well I dont see any correct method listed in the schematic instrucions other than if it needs extreme adjustment then something else is wrong. The crt is up against the rubber support that butts up to the main crt neck holding bracket. If I adjust the focus coil to center the image I guess it doesnt matter how crooked it looks. I have no idea if the crt is centered in the bracket that holds it as I cannot see anyting unless I take it all apart. Is the focus coil supposed to be butted up against the yoke? Does it matter where on the neck of the crt the focus coil is located? I do know that the ion magnet seems to move the picture around but if I make it max brightness then right side seems shadowed.

[bandersen]

Have you tried adjusting the screws in all four corners? Tighten and loosen to center the picture. The whole focus assembly can also be moved forward and back. Remember we aren't there. The more pictures the better. Take some from a few feet away so we can see the whole assembly from the top and sides.

I've repaired a few dozen of these Admirals and the only times I've seen anything like this was from mechanical issues with the CRT/yoke/focus coil mounting.

[fumplet]

focus coil to the max to try and get raster across screen. Raster is almost to the right side of screen. What does moving focus coil forward and back do?

[fumplet]

focus coil and crt setup side view. Sure enough focus knob is all the way to one side to get focus with focus coil cranked totally crooked just to center picture. So if the only thing left possably is mica caps.

[bandersen]

Moving the focus coil changes the strength of the magnetic field required to get a good focus. Since your focus control is at one extreme that tells me something is not right.

[bandersen]

Here are the best images I have showing the neck area from some 20B1s I worked on for what it's worth.

[fumplet]

Yes somethings not right and if I straighten out the focus coil, the focus knob setting also straightens out with sweet spot almost centered. I dont see how the crt couldnt be centered since its shoved into the rubber bracket coned gasket. Almost suspecting the crt itself. Notice how all your ion traps are close to up and down. I wonder if turning the crt clockwise would do something. No schematic diagram of crt mounting but is the yoke clamped to the neck whete i cannot see it? I Loosened the crt front strap to see if it would slide further rearwards. Seems like somethings holding it from sliding forwards even after ion trap magnet is loosened.

[bandersen]

The yoke is not clamped to the neck. There is a thumbscrew on top holding it in place.
The CRT is only held in place by that strap. There are rubber pads underneath that often fuse and harden to the glass. That's probably what is holding yours down.

A thin knife can be used to break the bond.

The CRT anode is facing up on mine and the ion trap magnet screws on top.

[Yamamaya42]

Originally Posted by bandersen

The yoke is not clamped to the neck. There is a thumbscrew on top holding it in place.
The CRT is only held in place by that strap. There are rubber pads underneath that often fuse and harden to the glass. That's probably what is holding yours down.

A thin knife can be used to break the bond.

The CRT anode is facing up on mine and the ion trap magnet screws on top.

There used to be some kind of solvent (spray) to help get the yoke off, but I have never seen it other than in old books from the 50s-60s. :O

I doubt it exists any more.

[fumplet]

Front of crt is loose when i removed the strap because the crt would come out a bit. I thought maybe the ion trap was holding it but no. I Was suprised something else was holding it in the bracket.

[bandersen]

A hair dryer or heat gun on low should help loosen the yoke if it's stuck on.

[fumplet]

Well I almost got picture tube out but tube socket wouldnt clear yoke, but Im not even sure I need to totally remove piccture tube unless possably somethings holding yoke from being straight against tube cone. I had forgotten about the little front tab on chassis holding tube in. I also wasnt aware that the top wing nut allows the yoke to be moved not only clockwise or anticlockwise but front and back. so i did slide yoke closer to front of tube. currently watching adam 12.
Im going to try to take the tube all the way out tonight. Might take 2 people to do it, one to hold the tube and other to get neck plug to clear yoke.

[fumplet]

Some of the yokes had resistors and capacitors in them i wonder if this one does will find out when i get the tube out

[bandersen]

t will definitely have two resistors - one across each vertical yoke winding. The are there to dampen any oscillations. There should also be a small mica cap across one of the horizontal yoke windings for the same purpose. I do not recommend messing with any of them.