Zenith 25EC58 Restoration Thread

[TinCanAlley]

The tripler has a 500ohm 7W resistor that is one of the cement (sandbox) type. Since I'm replacing the tripler I figured I'd go ahead and replace the resistor as well. Finding the cement ones is not easy, so I just ordered a WW in the proper resistance and wattage that is a 1%. It also has a temp of up to 250c.

[TinCanAlley]

Setup switch and tripler are installed. Just need for the RTV to set and I'll reinstall chassis and test.

I don't think I did too bad with the wiring and soldering. The resistor was a bit longer than the original, so I had to set it a bit higher up with a longer lead on the tripler end. A bigger blob of RTV covered the longer lead.

Always wondered about the focus control lead. It pretty much just runs along the top of all the circuits on its way to the pot. Wondering if it's a noisy lead or not enough to interfere with other components.

[TinCanAlley]

Well I'm 0 for 2, but there is a side benefit for the work I did.

The tripler is in and set is running, but the bars are still there. The only plus is I'm now able to fully focus to the sharpest image without the moire effect on the sides of the screen. Some of the pics I posted show it. Image is as sharp as can be and no signs of the moire effect.

The setup switch is working just like before, so I the switch isn't the issue. Of course I didn't touch the controls as I'm quite happy with the grayscale I have and I figure with the brightness I currently have, I should have seen some kind of line flipping the switch.

So now I'm pretty much at the point where the only things I haven't replaced are the yoke and flyback. Guess it's time to just button her up and enjoy watching while learning to ignore the bars when they appear in darker scenes.

[vol.2]

Originally Posted by TinCanAlley

So now I'm pretty much at the point where the only things I haven't replaced are the yoke and flyback. Guess it's time to just button her up and enjoy watching while learning to ignore the bars when they appear in darker scenes.

I don't think that replacing parts will get rid of the jailbars. I don't think it would in general

The way I understand it, jailbars can end up in older TVs because the manufacturing tolerances are much better now and newer parts are so good that they show the bars. The bars were always there, but the older parts had added impedance or more efficient transistor junctions, and thus do not inhibit them.

Finding the source of jailbars, as I understand it, it usually a process of putting blocking capacitors in different places to see if they change, or placing magnetic shielding around reactive components

Perhaps I'm mistaken though. There's a lot of older, more experienced people on the forum who would have a more reliable opinion

[TinCanAlley]

Originally Posted by vol.2

I don't think that replacing parts will get rid of the jailbars. I don't think it would in general

The way I understand it, jailbars can end up in older TVs because the manufacturing tolerances are much better now and newer parts are so good that they show the bars. The bars were always there, but the older parts had added impedance or more efficient transistor junctions, and thus do not inhibit them.

Finding the source of jailbars, as I understand it, it usually a process of putting blocking capacitors in different places to see if they change, or placing magnetic shielding around reactive components

Perhaps I'm mistaken though. There's a lot of older, more experienced people on the forum who would have a more reliable opinion

I was hopeful, but didn't get my hopes up. I read a few sites where someone fixed their jailbars by cleaning their CRT socket and replacing the tripler. It was the same chassis as mine. Also read where someone replaced their tripler and got jailbars. They went back to original and they were gone.

For the life of me I can't remember if the set had jailbars when I first got it. I remember it was in bad shape, calibration wise and I was told that before I do anything I needed to replace all the safety caps and then the electrolytics. If the jailbars were there to begin with, they might have been masked by all the bad calibration settings.

I've been watching a youtube channel where they show the results of tantalum caps across zener diodes and uses a device to "listen" to the noise from the diode before and after. They also show using other capacitors across other diodes. Doubt that's where my issue is, but interesting learning about controlling noise in circuits. I thinking that my issue might be with a decoupling cap. I've noted a couple on the schematics that are in the boost (750V and 240V). I figure I can note the solder pot from pics and then mark their topside connection and try adding another bypass cap and note the affect, if any, on the bars.

I going to make an uneducated guess here and say the new tripler has had some impact on HV. My static convergence was off after the swap. I had to readjust it and then a small dynamic adjustment. It's back to what it was, if not slightly better.

I'm going to pause my work on this set and move on to a 13" Hitachi that I'm using as my monitor for a TI-99/4A computer. Believe it or not, but it also has jailbars on the left side of the screen. I order new capacitors and am going to test the CRT. Beyond that, it isn't worth putting money into. Following that, I have a B&W RCA from '75. It blew the fuse a few years ago, but not since. I'm assuming the old fuse was tired. I figure I'll hook it up and let it run for a while and see if it acts up.

[vol.2]

jailbars are hard

[TinCanAlley]

Originally Posted by vol.2

jailbars are hard

I finally made some progress.....

I've been calibrating using the Video Essentials DVD and their pluge patterns and their instructions. This has always led to the image being dark on any other DVDs I've used, so I always adjust it. That has always led to jailbars. I decided to search for ways to adjust that differ from theirs. I think I've solved it and with decent results.

I started with contrast mid point. I then brough up brightness until the blacks were crushed and darker areas started turning grey. I then backed it off until blacks were black again. I then brought up the contrast to get a bright enough image. I'm positive this level of contrast is considered in the blooming range, but it has to be. Now all the programs I've tested show no jailbars at all. The image is very watchable, but I would like a little more light in the light areas, but to do so means bringing up the brightness and that crushes the blacks and brings up jailbars. I know it's been a while since I've adjusted and watched an old CRT television, so maybe I'm asking too much for the technology of 1974.

For testing I took my 13" Hitachi from 1981 and adjusted it the way I was the Zenith and I got faint jailbars. Readjusting the new way took them away and gave another very watchable, but not perfect, image.

So either this is a limitation of the technology, or I have an issue in the brightness/contrast circuit. Eitherway, I'm going to leave it be and enjoy it.

I'm now working on removing all the components of my 9-57 horizontal board so I can piggyback the 9-90 horizontal and be able to use a VCR without the waving at the top. I'm also hoping that the board will better center the image horizontally than the current module. It's about 1" or so more to the right than the last one that failed. Not only that, but I hope it solves another horizontal issue I'm having using the original 9-57 module. When the set it started cold, the image is messed up horizontally, but not like before when it was rolling out of sycn. It's a stationary issue and only goes away when I change channels and back, or sometimes on its own after a minute or so.

I wish I had to room for storing more stuff as there's someone near me giving away a 25EC58 chassis and same CRT as mine. Would be nice to have a spare I could use to compare or salvage for parts.

[TinCanAlley]

Well jailbars are gone and all out of spec parts replaced. Set is fully operational and working like a charm. Next is the touch up of paint and painting of stand.

Thanks for everyone's help. This thread is done.

[vol.2]

Originally Posted by TinCanAlley

Well jailbars are gone and all out of spec parts replaced. Set is fully operational and working like a charm. Next is the touch up of paint and painting of stand.

Thanks for everyone's help. This thread is done.

That's awesome. Would like to see some good photos of the finished set though!

Would be cool to see the case and also a decent close up of the video.

[ronl]

[TinCanAlley]

Originally Posted by vol.2

That's awesome. Would like to see some good photos of the finished set though!

Would be cool to see the case and also a decent close up of the video.

I still have to do some research on the cabinet paint. I am told it is lacquer and I don't think I've ever done anything with that kind of paint. I've see other's paint theirs completely, base and all, but they go with a bright white. From what I understand, the paint color used was and off white (imperial something). If I can't figure out how to touch it up and it not looking like I did, I'll repaint the entire cabinet in the original color, just won't be able to get it in lacquer.

A couple here helped me get my camera setting for taking pictures of the screen, but I don't know how to get video from my phone that is in synch with the screen. Also, I am not sure why every picture I take seems to magnify the phosphor dot patter.

[TinCanAlley]

Has to be a way to take a picture that accurately captures the image on screen. I took 40+ pics and these 2 were the best. I have a lower resolution Nikon SLR digital camera. I wonder if that one can be set properly for better images...???

[vol.2]

Originally Posted by TinCanAlley

Has to be a way to take a picture that accurately captures the image on screen. I took 40+ pics and these 2 were the best. I have a lower resolution Nikon SLR digital camera. I wonder if that one can be set properly for better images...???

Looks pretty good! The colors are definitely coming through, and I don't see any visual artifacts.

Yeah, taking pictures of a CRT can be tricky. I also will typically just take a bunch and pick the best.

I have found that the orientation of the CCD makes a huge difference though. Sometimes, if the picture is flashing too much, turning the camera 90 degrees will cure it. Sometimes it also requires that I move my camera closer or further away from the screen. Typically, I can get an acceptable picture by cycling through those two parameters (rotate camera, slowly move camera towards and away from CRT).

[TinCanAlley]

Originally Posted by vol.2

Looks pretty good! The colors are definitely coming through, and I don't see any visual artifacts.

Yeah, taking pictures of a CRT can be tricky. I also will typically just take a bunch and pick the best.

I have found that the orientation of the CCD makes a huge difference though. Sometimes, if the picture is flashing too much, turning the camera 90 degrees will cure it. Sometimes it also requires that I move my camera closer or further away from the screen. Typically, I can get an acceptable picture by cycling through those two parameters (rotate camera, slowly move camera towards and away from CRT).

I took so many pictures and ended up with 4 that I really liked, but still below in person visual quality. It's a bit annoying that in person I see scan lines, but not dot pattern in that line. In pics, it becomes quite noticeable with the higher resolutions. I think I'm going to wait til it's dark outside, setup a tripod, turn off all lights and try it that way. I'm sure the light behind the set is going to be picked up by the camera and it will adjust for that and might be part of my issue.

[TinCanAlley]

Thought I'd add something regarding the perforated cover over the swing door. I've noticed in a few pics I've seen on the internet that, like mine, many had dents in it. I had quite a few and some were pretty bad. Don't know what happened to it, but it had a rough life.

The cover is aluminum is held to the door by tabs that are left when the piece is cut to fit the door. Those tabs are bent over to hold it in place. If you carefully bend those tabs back, the mesh piece will come off. I took that piece, found the smoothest and flattest surface on which I placed the thickest piece of paper I could find to place between the surface and cover so as not to scratch it. With the cover face down, I gently tapped the dented areas with a flathead hammer until it was smooth as possible. Flipping it over often to see the progress. When it was done I put it back and bent the tabs over. I wouldn't recommend taking it off too often as the tabs will break.

The results are great. It's only under close inspection you can see it isn't perfect.

The after pic isn't the best angle, but I am too lazy to take a proper pic. Also, looking at the pic, I need to remove the transducer and clean the screen and opening.