Hello again, all. Hopefully this post is not too far off topic. It's not really "vintage" repair, per se.
By suggestion, I recently picked up a Knox Video Studio 40.ND video character generator. Because you won't find much of anything about it online, I'll tell you a little bit about it. This unit can do not only full page titles in color and with a few different fonts, but also crawling and rolling titles. A solid background color can be displayed or the background made transparent so that incoming video will show through. My example was made in 1997.
Two video inputs are available, for either composite or Y/C video signals. A switch at the back lets you choose which type of input signal you will use.
The character generation part of things seems to work just fine.
It's when you display video from either of the two inputs that it becomes obvious something is terribly wrong.
I have more captures of the output
here.
When I first got the unit, there was essentially no color at all when inputting a video signal. Only later did I notice that one object, a particularly bright red record album sleeve, had something of a "beating" or "pulsating" green color halo around it.
Finally I started to look at the chroma handling circuitry inside this unit. A Harris/Intersil CA3126E chroma processor IC is used. From what I could see, all voltages and the color clock signal (3.579 MHz) looked to be OK. So I turned my attention to the input end of things when I noticed that putting my finger on the chroma input pin of the IC would result in dramatic color changes. And then I found what I
thought was the problem...a capacitor in series with the chroma input. Substituting a good capacitor resulted in the correct colors appearing. Well, that was an easy enough fix.
When I soldered the new capacitor in, things were bad once again. I tried another capacitor just to be sure I hadn't damaged the first while soldering it in. There was no improvement.
I looked again at the clock frequencies going to and from the CA3126E chip. On pin 6 (VCO input) I got a reading that differed somewhat from pin 7#(VCO output, 3.579 MHz) and pin 8 (carrier output, 3.579 MHz). I've forgotten the reading from pin 6, but can get it again. I want to say it was around 3.35 MHz.
Removing the CA3126E results in loss of all color for both input video and generated characters. Luminance output continues to function.
Knox Video was of absolutely no help. (Frankly, I find it inexcusable for any company selling products to a professional market to not support them for as long as they are in business.) They ignored my e-mail and when I called, told me that they had thrown everything away concerning this unit while cleaning their office.
I'm stumped. I want to suspect the IC at this point, but I don't feel that I've got enough proof to do so. I'm kind of starting to reach the point where I feel like slinging it into the "stuff for recycling" bin because I'm getting nowhere at this point.
There's a video
here showing the defect in all of its glory. Note how the color is unstable at times, especially with regard to that router.