I have a DSR-505 that I've been using since the beginning of the month. One of the strange problems that I have been having with it is the signal to the TV dropping when I go to the guide.

It seems to only do this on SD channels. When I go to the guide on an HD channel, it always works.

What happens is if I am on an SD channel and hit the guide button, my TV will go blank for a sec as if it is changing resolutions which is fine, but then once it gets to the guide the TV flashes no signal, shows the guide for a second and then goes back to no signal and repeats. When it does show the guide for that one second, the picture is very shaky and wierd. When it actually does work, which it does sometime, the screen seems to be be jittery and unstable.

I have changed the cable and that did seem to help, but it still happens occasionally. The only thing that I can think of might be the cause is that there is too much blue or something, and the cable is having trouble handling it, although I have a hard time believing that that is the problem.

Has anyone else experienced this? Any suggestions?

Mine flickers a bit as well but recovers nicely.
Your set is struggling with the video changes.

Try locking the red button settings to 1080i or 720p or Native and see if any of those improve the situation.

I lock my own tv in at 1080i as ARR said and it does improve the flicker. However, when I do that, the outbound coax to the tv in the bedroom no longer feeds. The box can't seem to handle multiple simultaneous outputs unless you leave the setting at 0000.

What do you mean by "red button settings"? Are you referring to the button on the front of the receiver that will set the resolution to whatever? What will the display read if I set it to native?

That's the correct button. When set to native mode, the display will read 0000.