Toshiba Warp - Newbie

[maffewl]

First off, hey everyone!  Looking to build my first MAME... just waiting on some shipments.  Been reading a ton, but am a complete noob so sorry if I ask some dumb questions in the coming days/weeks/months.   

I have an old HP Mediacenter PC (circa approx. 2001-2) that I'm going to use as the brains with a P4 Intel and the graphic card has a S-video out. 

Anyways, I just purchased a 27" Toshiba t.v. and plugged it up... everything seems to work well except there is a slight warp/distortion at the top and bottom of the screen (see pic).  I checked the t.v. and this is only happening with the computer input.  Cable shows fine.  Just curious if anyone could help with what might be causing this... I could live with it if need be, but if it's fixable, I'm open to suggestions.

Please talk to me like I'm a 5 year old with some of the terminology... I still don't understand kHz and 480p vs 480i talk, eventhough I've been reading about it for a week now... 

Thanks ahead for any help 

[mamenewb100]

Is this an old school curved screen TV? If so, I'm assuming Windows is detecting the correct resolution of your Television and since tubes are generally curved.. so is the picture. Cable TV probably just outputs a generic signal to match the signal of your monitor and doesn't use the exact number of pixels on your screen.

You could make a customized resolution that would shrink the picture a little and give you a flat window on the top and bottom. Using a program like Powerstrip allows you to do this.

[maffewl]

Thanks for your response...

It is an old school CRT t.v.  I might try the resolution change and see if that helps... the only thing that makes me think it might be something else is that it does not curve symmetrically with the t.v.  The warp/distortion starts small in the upper left corner, and gets larger in the upper right corner... there is a slight slant from left to right.  And along the slant is a gradual dip, again, off center.

[MonMotha]

Aside from being incredibly out of focus (could just be your camera) and overly hot (brightness/contrast, again, could just be your camera), it looks about like what I'd expect.

Television uses "overscan" to attempt to hide imperfections in edge geometry.  Basically, the picture is extended beyond the edge of the visible area of the tube.  The TV production guys know this, so they don't put anything important in that area, but they put reasonable content there so that you can't easily tell where it's supposed to end.

PCs don't do this since usually every little detail is important on PC graphics.  Unfortunately, this causes some problems when working with a TV.  Sometimes you can go into service mode and tweak the picture so it will at least fill the screen, but don't expect perfectly straight edges no matter how much tweaking you get.  This was tough to attain even on high end CRT PC monitors.  If you can't get into service mode, you can adjust the blanking intervals in your video modeline to attempt to make it fill the screen, but this isn't exactly a fun process.

[maffewl]

So it sounds like my fix will be a strip of electrical tape at the top and bottom. 

I'm going to be using tinted glass for the cab, so it shouldn't be noticeable, although I will still probably mess with the resolution and Powerstrip (even-though I looked at the software, I don't have a clue what most of the inputs are). 

The odd thing to me is that the distortion is off-center and slanted, I would have expected it to be at least even... will a resolution change allow it to be symetrical?

And, you are right about the pic, it was taken with my cell phone and looks pretty horrible, but demonstrates the point.

[maffewl]

OK... so I noticed that the whole image is slightly rotated clockwise...

I just noticed this... I thought it was just the top and bottom but it looks like the picture itself has a slight clockwise rotation... is there anything I can do to fix this?

[MonMotha]

There may be a rotate option in the service menu.  Most TVs don't have this control, though, since it involves extra hardware (= $$$).  Again, the overscan on conventional TV largely hides this effect, so most TV makers don't bother to get it spot on.

Otherwise, you'd have to rotate the yoke.  Simply put, it's not worth bothering, especially if you're new to things and the problem is relatively minor.

[maffewl]

I appreciate the response MonMotha.  You re-affirmed what I've been reading about the issue online.  I guess I will just have to live with it, or I may just give it to a family member and buy a different tube.  Thanks again for the help!