I have a sony crt hd widescreen TV that has hdmi input.
Got a comcast HD cable box.
Been having problems where I go to HD channel, TV does it's weird conversion flickering thing every time it goes from SD to HD. Then a lot of times (but not all the time) if I go back to a standard def channel, I get a weird green and purple tinted picture.
Now, before, I could cycle through the inputs on the TV and go back to the HDMI, and it would be fine again on the analog channel.
But now it doesn't seem to help since I put an hdmi switcher in between the Cable box and the TV.
The cable box has a DVI output and came with a DVI to HDMI cord. I'm wondering if that has something to do with the green purple problem?
Could it be that the DVI to HDMI cord doesn't have the copyright protection complacency that HDMI and electronic components have?

I don't want to go through the effort of getting another box if it's going to do the same thing. Besides, if I have a problem, I want to learn all about it, why it's happening and also a solution. I'm an optimist that way, a good must come out of a bad situation type of person.

Well, if it doesn't happen all the time, it probably isn't the digital wire. If it was component, maybe a wire issue could do something like this colorful problem. But with digital, wire issues are either no picture, or pixellating/some missing picture.

It always seems to be the cable box. But they should have HDMI models, now. Maybe you just need to upgrade, anyway.

Short term, try flipping inputs on the switcher instead of the TV to see if that restores the pic.

Does your cable box have an option to override the signal? I have a Scientific Atlanta and it lets me set it so that every channel is displayed in 1080i; there's no switch from SD to HD. If your box has this option it might resolve the problem you're having.

I should look into that! I'm assuming that's in the setup menu?

My box is silver and not sure of the brand, but looks like an upgrade to the popular motorola digital boxes with the big clock and channel yellow led window in the middle.

I had the same problem.

Check out this site and see if that doesn't help fix it for you. Been a while since I've had to do it, but I think you have to change the setting on the 4:3 override.

I do have a motorola box with dvi output and a supplied dvi to hdmi cord.

I did discover how to get into that menu by way of a comcast on demand tutorial. But in that tutorial they show off hdmi out boxes instead of my dvi out box. I only have the 4:3 override option and not the HDMI/YPbPr Output option I'm pretty sure. After reading the link you gave me I'll have to try switching the 4:3 option to Off and see what happens.

You said you had that problem, what do you think fixed it?

You don't mention if that box is a DVR or not. I understand wanting to hold onto it if it is and you have a bunch of saved programs on it. But if it's not, bring it back to Comcast and get one that has an HDMI port on it. I'm sure that it wouldn't be a problem. Those boxes with the DVI port are probably several years old.

OK so I tried the menu again this morning. It does have a DVI/YPbPr Output option, but that's not the problem. Found out the default option of the 4:3 override is 4:3 and not "off". So I switched it to off and I think my problem is now solved! Not only does switching back and forth from 4:3 SD to 16:9 HD not give me any funky green and purple colors, the scramble black screen goes away as well. I always thought that was the TV doing that when it switches to HD!
But no, it isn't a DVR.
And do you think the HDMI output box instead of the DVI output box will make much of a difference?

Newer is almost always better. A newer box would probably have improved processing, especially for analog channels. Plus, you would be able to pass the audio as well as the video over the HDMI cable, so everything is digital. Probably won't make much of a difference through TV speakers, but it wouldn't hurt.