Quote:
Originally Posted by Tom Albrecht
It's a little hard to know what things in your picture are supposed to be there and what are not.
A darkening of the background along a horizontal band which includes very brught features is not caused by the CRT. This is caused by 1) lack of DC restoration in the set, which is a design decision made to reduce cost, and 2) possible misalignment of the video IF, resulting in insufficient low frequency response in the video. Often the setting of the fine tuning has some effect on the second item -- you can trade off high frequency (sharp features) for better low frequency response (better blacks and whites over large areas). A well aligned set won't have too much problem with this however.
Usually the lack of DC restoration in sets of this era doesn't show up so much in terms of bands within the frame, but rather a general "greying out" of scenes that are supposed to be mainly black or mainly white.
You also have a little of the "faint white line" syndrome on your Predicta. The faint light vertical line just to the left of center is caused by a particular pulse on modern video signals during the retrace that wasn't used in the 1960s. Adding about a 30 pF cap to filter the video output helps solve this problem. If you search on "faint white line Predicta" you can probably find some previous threads on this subject on how to install the cap that fixes it fairly well. Here's one thread on the subject: http://www.antiqueradios.com/forums/...72667&start=80 . |
Thanks for the info, I actually already read that entire thread last night trying to search for a solution to my problem. You are right, the vertical line is there also, but it is not as distracting as my other issue. And adjusting the fine tuning will reduce the vertical line while the contrast streaking not as much. Where on the chassis would I put the 30pf cap?
As far as the screen shot, the background "space" shot should be a uniform black, but as you can see it is split into horizontal sections of varying brightness. These sections are caused by smaller bright text or objects in the scene.
I have added another picture a little washed out due to my camera.