It seems there almost has to be a way to set the STB for 480i output over Composite Yellow, or why have Composite... it can't handle any Progressive signal. That's why they developed Component RGB. Some devices do that automatically, no matter what the Progressive setting (like my Pioneer DVR-640)? Maybe you have to turn Progressive off?
However, if you just can't get composite Yellow to work the way you want, there are converters described here that will take a HDMI or Component signal and convert it to Composite Yellow oir S-Video.
Click the 1st link in my sig. for the main thread on these units and lots of info and help files.
If your not using the component output one of those cheap component to S-video converters would work but only the more expensive ones have component passthru to also run to your TV.
Try different composite jacks on your Magnavox, both front and rear- its possible you have a dead jack (unlikely, but possible). Try a different wire (swap one of the audio wires for the video): maybe a bad wire.
Composite is locked at 480i, so no matter what resolution you choose on your STB the composite output will always be 480i (even if the component output is set to 720p). Each STB has different capabilities: the older ones had separate jacks for composite (yellow) and component (green-blue-red), and could usually send 480i thru the yellow jack and 720 or 1080 thru the component jacks at the same time, to feed both a recorder and a TV. Some of the newer boxes allow just one connection at a time: if you have one of those boxes it will have a menu setting somewhere to choose which output you want to use.
I've never seen a STB that does not offer a 480i option along with 480p, 720p, and 1080i. There has to be some way to select that setting, if all else fails contact the service dept of your cable or satellite provider for help. If it turns out there really is no 480i setting in the box, it may be just a limitation of the component outputs, but the composite is 480i for sure so there wouldn't be any other resolution choices for it (it should just work).
By the way, for your own information, I also did connect that composite output from my STB directly to my Panasonic tv and pressed the INFO on the remote, which indicated that it was indeed a 480P signal. Go figure !!!!!
Thanks for any replies.
Looks like we misunderstood, and your future is now.
Regarding these converters, they come in roughly two quality/price categories: about $50 and adequate, or about $300 and excellent. The converters that sell for less than $100 generally have compromised PQ with issues ranging from softness/muddiness to incorrect IRE level (making dark areas of the video blend together and lose details). The expensive converters give a much clearer signal, but they are pricey. Unlike some other electronics where you can get away fairly cheaply, with converters you do unfortunately "get what you pay for" (more $$$ = better quality).
The $50 converters are usable if you aren't too picky, and willing to accepted compromised PQ in exchange for a full 16:9 signal to your recorder. I've been experimenting quite a bit with the MonoPrice component converter, as well as a similar unit that converts HDMI to S-Video. On the whole, I think I get better video quality recording the standard 4:3 letterbox output of my cable box and zooming it with my TV (the color is better from letterbox, and any detail advantage of "true" 16:9 is killed by the muddiness of the conversion). I now limit my converter use to occasions when I forget to record a TV series episode from my off-air antenna in 16:9, and need to get it from cable on-demand. Using the converter keeps the entire set of episodes matched in 16:9, and current TV series are "punchy" enough to survive a cheap converter. I would avoid using the cheap converter for a movie or other spectacle where the cinematography is important: you'll get cleaner results zooming into the letterbox 4:3 output of your decoder box.
Note some of the first-generation DVD recorders actually did have component inputs, and were capable of internal conversion to pass thru their composite and S-Video output jacks. Using one of these older recorders as a "converter" nets PQ somewhere between the cheap $50 converters and the excellent $300 converters. The drawback is you need to find such a recorder, they take up a lot of space, and draw more power (because you'd be leaving it on all the time). The most common and inexpensive recorder with component conversion feature was the Philips DVDR72, circa 2004. These pop up for approx $50-$70 on Craigs List and eBay. The recorder doesn't have to be fully functional, it just needs to power up (you won't be using its DVD drive, which is most likely broken anyway).
I have two Monoprice Lenkeng converters, an Audio Authority converter, and an Atlona converter. The Monoprice converters cost about $40. The other two list at about $300. The more expensive ones usually provide a sharper picture, but have problems of their own. They make darkened scenes too dark. They have problems locking on to SD signals that are letterboxed. Also, both of my expensive ones have an occasional quirk where there is a horizontal interface line that seems to be caused by the lower half of the frame being delayed, so that it doesn't quite match the top half of the frame, especially when there is horizontal movement in the scene. When recording from an SD source, I prefer to use S-Video, direct from the source, usually one of my DVRs. I only use a converter when I want to make an anamorphic DVD from a HD source.