Zenith 25EC58 Restoration Thread

[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]

[Electronic M]

Which part was causing the jailbars?

This thread started getting too verbose and shotgunny and I tuned out a few pages in.

[TinCanAlley]

The service manual has it as video amp 4, but it's actually 3 and the set doesn't have a 4. Anyway, I replaced the 24V Zener and the .001 1KV decoupling cap on that's amp's transistor. While many said the ringing I see when I scope the ABL, and along that path, wasn't the source of the bars, it quite possibly was. I tried cleaning up the ringing from the source, but I didn't know enough to do that. The ABL's collector is sourced from the tripler. The 500ohm resistor goes to a 7.5V zener and spark gap. The Zener is on the wiper of the ABL pot which feeds the ABL transistor. I noticed that if I turned the pot, the bars changed intensity. Not much, but noticeable. I then set the ABL per SM and started tracing the circuit better. I found that the brightness, contrast, ABL, Blanker, etc. all came together and funneled into the video amp. Looking closer I noticed the zener on the transistor base and the decoupling capacitor. Didn't bother doing one than the other to see, just did both as I had them.

Anyway, while the bars are gone for standard viewing, I can still make them appear faintly if I crank the brighness and contrast beyond what is normal levels, but at the normal levels for viewing, even dark scenes, they're gone.

[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.