Nasty A8 output on modern LCD TV

Entry posted by Stephen December 8, 2010

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I know this has been discussed quite a bit previously. Just wanted to get some pictures. The output is from two different NTSC 130XEs via a separate Y/C (s-vid) cable. One of the machines is completely stock, the other has the full super-vid mod as well as removal of the RF modulator. The TV is a Dynex 22" LCD 720p.

The first issue with modern sets is the incorrect de-interlacing of the A8 signal. Every other frame is dropped by a scanline. This makes sense due to the fact that the A8 is not sending an interlaced signal - every frame is exact and also an even # of lines. Another side effect is the display only gives a 30Hz screen update. There is no flicker in "page-flipping" modes, but the downside is straight lines are not.

This is a screenshot of FlickerTerm. Note the staggered line which should be straight.

The other thing to note is the terrible vertical banding.

Here's where it gets interesting. When I bring up the help screen, the border changes to the same color as the main screen. The vertical banding disappears. Unfortunately, this does not happen in BASIC just by setting the screen & border to the same color. FlickerTerm must be doing something to the display list.

Here is another shot of the banding when using the TV's s-video input.

This is the same system running through my scan doubler into the VGA input. It suffers the same "stagger" effect in FlickerTerm but the banding is much much less prominent.