Howdy ya'll,
This is my first TV restoration job. The lowdown is that the set had a totally dead picture tube. The original was a 21ZP4 which I replaced with a 21YP4A that is a NOS tube.

You can follow along with the restoration here:
http://www.antiqueradios.com/forums/viewtopic.php?f=3&t=213720&start=140

I've recapped the set and tested it afterwards. As I've never done this before I had some questions.

First of all- I am getting no picture. The filaments on the picture tube are working. I also believe the flyback is working properly because I get a nice, healthy 'snap' when I discharge the tube. But there seems to be no sound. Just a slight hum and a crackle when I adjust the volume.

However, I made no adjustments. I simply stuck the ion trap back on and also installed the yoke as-is as well from the old tube. The new tube is very different in that for starters, its aluminized and for a weird reason also using a angled gun. Being that this is an aluminized screen I removed the permanent magnets from the yoke assembly.

I've been doing some research as how to do this. Yesterday I didn't realize that there was such a big difference on whether the trap was adjusted correctly or not, ( be easy on me... I'm a newbie!) so when I get home I'll try that. But in addition, are there other adjustments to the yoke assembly/ electromagnetic focus I should be making as well? Could a ion trap out of whack actually cause there to be no picture? What about the electromagnetic focus?

Just seeking some additional opinions before proceeding...

Hi and welcome to VideoKarma. Those magnets on the yoke were probably for centering and you should keep them installed.

Yes, the position of the ion trap magnets on the CRT neck are crucial to seeing a picture. Just a slight misadjustment will cause it to go dark.

The new 21YP4 uses electrostatic focus so you should remove the electromagnetic focus ring for the neck if you have it installed. Pin 6 (G4 focus voltage) should be connected to something in the -64 to +350 volt range. Often it's just shorted to either G1 or G2.

Misadjusted ion trap can cause a dark screen.
Start with the open end toward the high voltage anode connector, about an inch forward of the bakelite socket. Adjust for max brightness. If no success move the ion trap 180 degrees and retry.

There may be several problems, one causing dark screen and another causing no pix, no sound. Get the screen lit first.

Don

The Magnets you removed were for Focusing, since teh 21YP4 is Electrostatically focused it should be OK (actually required) to remove them.

YOu can focus the tube either by leaving the focus pin disconnected or by applying some B+ to it, whichever gives the best results.

The Ion Trap is absolutely critical, misadjusted will give a dark screen at least and damage the tube at worst. It's adjusted for best brightness and focus, it is also directional front to rear and it may be the wrong trap if it's off the 21ZP4.

Thanks.
Ok, so here's an update. The good: I was able to get sound and a raster.
The bad: All I'm getting is a horizontal line that takes up about 30% of the screen as seen here:
http://i188.photobucket.com/albums/z4/pvmowerracing/390EC178-7CF4-4B5A-ADFB-A33E1F6DB651-231-000000EF89078DA2_zps00f5b0bd.jpg

I fiddled with the vert, horiz, and width controls to no real avail. Adjusting vertical all the way basically makes the picture disappear.

yesterday I had checked the resistors ( or at least I think most of them) and all were within 20% spec. All electrolytics have been replaced and the rest are ceramic disc. I don't have a tube checker for TV tubes so as far as their quality... not sure. Oh- and I'll 'fess up' that I somehow embarrassingly installed one of the new caps backwards initially, turned the set on, saw a wisp of smoke, and installed another correctly. The resistor connected to the other end was nice and toasty looking but still tested within spec as did the rest in the circuit. Not sure that is worth mentioning but oh well..

should be connected to something in the -64 to +350 volt range. Often it's just shorted to either G1 or G2. Does that refer to jumping from pin 1 or 2 from the base of the picture tube?

Thanks in advance...

There is a horizontal frequency adjustment on top of the chassis behind the UHF tuner indicator. It acts like a horizontal hold, only much broader. Center the hold control and adjust the frequency for a stable picture. Then adjust vertical hold to stop any rolling.

Next, adjust height, v lin and centering for a full picture. Centering may be a problem since the centering was part of the focus magnet.

Proper alignment of the horizontal oscillator is simple, but keep us up and we will advise as we go. It's a mix of horizontal freq, hold and coil adjustments, all done from the top of the chassis.

Jumper pin 10 to pin 6 on the CRT socket for focus voltage. Use a thin piece of bare wire so the socket can be put back easily.

Don

Yes, as a matter of fact I do recall seeing that control topside of the chassis but was unaware of what it was for. So I'll try that as well.

When you removed the Focus magnets you may have also removed the centering magnets. That part slides up and down, side to side as I recall, the Focus is controlled by the flexible "Speedometer Cable" sticking out of the rear that moves the focus magnets back and forth.
I'm not sure you can actually remove one and not the other on this set.

The magnets I removed were permanent magnets attached to the rear of the yoke assembly. These were controlled via a little knurled nut you could twist to move the whole permanent magnet assembly forward and back. Here's a pic of what they look like:
http://i188.photobucket.com/albums/z4/pvmowerracing/8E773F05-76AB-400F-86A1-8542761CEC0E-231-0000001E566AA07D_zps1762ee1d.jpg

Yep, that's the Focus assembly but the lever with the Wing Nut is for centering the picture, it slides up and down and side to side.

Since your tube is electrostatically focused you probably do need to remove the focus magnets but you still need to find a way to center the picture.
I'm not sure if the focus magneta also provide the magnetism for the centering rings or not.
It might be possible to retrofit some centering rings off of another set that used electrostatic focus, they are just mounted on a plastic cover that goes over the back of the yoke.

You might try it with the whole assembly put back in place and see if it interferes with the Ion trap or not.

I guess i'm a little confused, did you remove the entire assembly or just take the magnets out of it and reinstall it?
Possibly the centering control might still work if you left it in place.

Yes the magnets were just held in by pressure so they came out when the back plate was loosened. Is it going to hurt anything to put them back in to see what happens?

No.

You mentioned adjusting the vert pot to one end would kill the picture? I wouldn't focus too much on it just yet, but it could be a bad pot. Double check to make sure there are no paper caps left in the vert circuit, that is one place that is intolerant of old caps.

Well,
Got some better news. I got it to basically work in the crudest sense of the word. This is more or less a repeat from another forum, so sorry if some of you radio guys are on here:

I found a schematic and it was worth every penny. I was reading through it and paid careful attention to the video output and oscillator circuits. For the oscillator there had been a bumblebee cap installed. As I had no schematic I read the color code as a .001 going to the N0.2 pin of 12HU7. In fact it was a .1, which is a considerable difference.

This made a very big difference and now the picture fills the screen. There still remains a few issues. But th good news is that the set " works" in the crudest sort of way.

1: Sound is intermittent. Last night 6T8 showed up as shorting and it was jumpin' all over the gauge. So I know its bad but I have no spares. This is labeled as a" Ratio DET AF AMP" tube. I assume that meand Audio Frequency Amp. If so, I am guessing that's the problem.

2: The sharpness isn't what I'd call fantastic. Then again, not sure how great these old sets are.

3: Biggest issue is the whole picture goes to the right. I can't get the image to go all the way over so there's about 2" of blank screen. Seems like no adjustment makes any difference.

http://i188.photobucket.com/albums/z4/pvmowerracing/51A36166-2890-4551-96A4-5F462BD06778-1409-00000159B4270C37_zps1e663971.jpg

Here's a Video:
http://i188.photobucket.com/albums/z4/pvmowerracing/th_99E6CEF4-0048-44BE-8A66-217F73B2F28B-1409-000001591269FB1C_zps0f7ca7a7.jpg (http://s188.photobucket.com/albums/z4/pvmowerracing/?action=view&current=99E6CEF4-0048-44BE-8A66-217F73B2F28B-1409-000001591269FB1C_zps0f7ca7a7.mp4)

The sharpness isn't that great because you replaced a magnetically focused tube with one that is electrically focused, you can probably improve it by applying some B+ voltage to the focus pin, it's usually the one all by itself 180 degrees from the other pins. Sometimes they focus OK with no voltage on the pin.

The centering is off because you took off the centering control, or at least the magnets. It may still work, try loosening the wing nut and slide the lever around and see if it makes any difference, regardless of the CRT type it should still work.

Removing the magnets is something that shouldn't be done, once you disassemble that focus assembly it will never work properly again even if you put the correct CRT back in, there is a polarity to the magnets and it's unlikely you would get them all back in correctly, however the centering portion may still work.

Removing the magnets is something that shouldn't be done, once you disassemble that focus assembly it will never work properly again even if you put the correct CRT back in, there is a polarity to the magnets and it's unlikely you would get them all back in correctly, however the centering portion may still work.

Hmm... maybe I misunderstood what some others were telling me, which was to remove the permanent magnets from the assembly. On this one the magnets simply are held in place with pressure. There are 4 of them and they are are in a concave shape that fit slots shaped to accept them. Each one is for the different sides ( top, bottom, right, left). So one idea I had was maybe to try and stick one of the magnets- the right side- back into the holder to see if this would 'pull' the image to the left up front...

I guess the problem her is that you don't need the focus part but do need the centering part and since they are part of the same assembly it presents a problem.

It should be possible to use a small magnet or the centering rings from a different type set to pull the picture back in line, you probably should just remove the entire focus/centering assembly so you can put the centering magnet far enough forward that it doesn't interfere with the Ion trap function.
It needs to be directly behind the yoke.

I guess the problem her is that you don't need the focus part but do need the centering part and since they are part of the same assembly it presents a problem.

It should be possible to use a small magnet or the centering rings from a different type set to pull the picture back in line, you probably should just remove the entire focus/centering assembly so you can put the centering magnet far enough forward that it doesn't interfere with the Ion trap function.
It needs to be directly behind the yoke.
I was just wondering if a purity ring from a delta gun rectangular CRT, such as a 25xp22 would work? If the blue lateral magnet is a part of it, it would have to be removed.
Just a thought!
On some of the early sets that had an electrostatically focused CRT, they used a centering device, that was not part of the yoke cover. :yes:

But what I'm wondering is this:
The original focus magnet assembly is directly behind the yoke. There were 4 magnets mounted in place before and they drop out whenever you loosen the back plate of the magnet assembly. If I were to re-install only the left side focus magnet, would this in effect cause the picture to shift over since at that point there would only be a magnetic pull to one side? I know that sounds incredibly goofy, but it'd basically be sticking a magnet to one side of the back of the yoke.

That might work but it would be very lucky if you got exactly the right amount of shift you needed, there's also the up and down position to consider.

Centering magnets aren't very powerful, it might be possible to get a couple small hobby type magnets and pay around with them until you get it right but it might be easier to find the rear yoke cover with the rings on it already.

I'll try that then and see what happens. And as a stupid newbie concern, if I do this I'm not risking ruining the tube am I? The magnets that came off of the focus assembly are fairly thick, chunky things. Here they are, all stuck together:
http://i188.photobucket.com/albums/z4/pvmowerracing/8E773F05-76AB-400F-86A1-8542761CEC0E-231-0000001E566AA07D_zps1762ee1d.jpg