Fada Restoration Gone Wrong

[southernguy]

About a month ago I started my Fada restoration project and everything went very well up until the other day. This is a Fada model 21T, the CRT is a 21EP4. All the electrolytic and paper caps have been replaced. I checked the wires and resistors, everything seemed ok, so I went ahead with a slow start. The set came right up with sound, then I was greeted with a nice bright test pattern. Then I cleaned up the cabinet with a new finish and started to put everything back together. After all that I noticed the image on the screen was tilted a little bit. What should of been a simple adjustment to the yoke turned out to be a nightmare. The Insulator between the deflection yoke and focus magnet was wasting away more in the center area than it was around the outside area exposing a solder joint with the back of the focus magnet. Needless to say as soon as I put my hand on the thing I was greeted with a spark and insulator pieces went everywhere. After quickly cutting power off to the set, I took the focus magnet off and saw what had happened. At that point I thought, maybe everything would be ok but i needed some type of insulator. I took the cover off of a blue storage tote lid and made an insulator, powered the set up and O crap what did I do. The image on the screen is all screwed up. At first there was no light on the screen, as a result the ion trap has to be right against the focus magnet. Not where it was before this happened. The left side of the screen is completely dark with an off center image. Rotating the yoke has little or no effect on the left side off the screen. (second pic below is before this happened) I hope someone can shed some light on this problem and point in the right direction. but I think i might have damaged the crt as the yoke seems to be working.

[bgadow]

I can't think of any way this could happen internally-it has to be something with the yoke. Is the winding itself moving when you adjust the hardware?

[Electronic M]

If you can get video, and did not short any wires on the CRT socket to anything then your CRT is probably just fine.

The first screen shot looks good. I'll assume it is a before shot.

The other two show what is called a "neck shadow" effect which is generally caused by the yoke being too far back from the face of the CRT or a miss adjusted ion trap.

The raster also appears to have shrunken. There are often resistors and capacitors inside the rear yoke cover, and since the yoke terminal(s) shorted to ground through the chassis housing (if I'm correctly interpreting what you wrote) then it is possible that one of those resistors (not likely to be a cap, but stranger things have happened) had excessive current through it it could have changed value affecting the operation of the horizontal stage. I'd check those resistors, and the circuit driving the horizontal winding of the yoke, and probably readjust the horizontal stage afterwards.

It is possible that the short caused a temporarily stronger magnetic field from the yoke which may have partially degaussed the ion trap magnet thus weakening it's effectiveness. If you have a spare ion trap magnet you should test it on the set.....Also try taking the ion trap magnet off and flipping it 180 degrees so the side that faced the screen faces away and see if that improves things.

[southernguy]

Yep, i can see it move, and it will rotate the Distorted image on the screen but the shadow on the left side is fixed and will not rotate with it. seems like it should move even if there is a problem with yoke. There is at least one cap and two resistors that I will try to change out.

[Electronic M]

Also forgot to mention the tilt and position of the focus coil, and ion trap position can have a strong effect on the neck shadow.

[Eric H]

This is a mechanical problem for sure, the CRT is fine.

First be sure the Yoke windings are snug against the bell of the CRT.

That wing nut on top holds the centering magnet, if you loosen it and move it around you'll get the picture to center, I think you will find it not only turns but it slides up and down and sideways, it can be a pain to get right, my Philco with a 21EP4 uses the same setup.

Do not under any circumstances disassemble the Focus assembly, that is don't take out the screws and remove the magnets, it'll never work right again if you do.
If the focus adjustment won't turn freely just clean and oil it but don't take it apart.

There is some interaction between the Ion trap, Focus and the Centering so you'll have to repeat the adjustments to get it right, adjusting the Ion trap should be the last adjustment you make.

[vts1134]

I love how many pictures of sets here include an adorable cat .

[kvflyer]

Originally Posted by vts1134

I love how many pictures of sets here include an adorable cat .

So do I! But I have four of those rascals and they love grill cloth.

Anyway, any progress with the yoke/focus/trap?

[edison64]

Hey what can you say.. all cat owners know that cats love boxes ..to the cats, we collect fancy boxes complete with fancy play toys inside...

[kx250rider]

Pics # 2 & 3 are classic misadjsuted and/or mis-placed focus coil. If it won't correct by adjusting the position of the coil ass'y, I bet that the metal around the focus coil got magnetized when the focus coil (if electric) shorted to ground, or when the yoke did, if that's a PM type focus magnet. That would cause the focus coil to have a super-electromagnet spot for a split second, and that could/would magnetize anything around it. Use a color TV degaussing coil and degauss the whole area of the focus coil, and the yoke brackets, and even the gun. Then if it's still off, I'd say that maybe the focus coil was damaged internally (a few shorted turns?), but HIGHLY unlikely, and I can't see how that would rotate the image.

Charles

[Eric H]

Adjust the centering lever before you degauss anything, if you degauss the focus magnets or the centering ring you will have a big problem.

[Penthode]

There is no reason to degauss a black and white set. Something has shifted and simply needs to be adjusted back.

[old_coot88]

Originally Posted by Penthode

There is no reason to degauss a black and white set. Something has shifted and simply needs to be adjusted back.

Agreed 100%.

[kvflyer]

Originally Posted by Penthode

There is no reason to degauss a black and white set. Something has shifted and simply needs to be adjusted back.

Absolutely...

[southernguy]

I would like to think everyone here for the advice. Eric, also thank you for letting me know not to take the focus assembly apart, otherwise I might of done that out of frustration. Turns out, the slider on the focus assembly was moving, but not all the way as it should. After taking it off and adding a little oil, I then saw how this thing is suppose to move. Also there was dust and flakes of insulator under the yoke windings, got rid of that. I used little bit of electrical tape to cover solder joints on the yoke to keep from shorting anything out. Put it back together, made the adjustments, and its a beauty.

I have four cats myself. The Cat in the first Photo is Osiris. He tends to keep the others away grill cloth.