Tapper cart - vertical hold issue?

[troff]

I just picked up a loose Tapper cart in my local retro video games store. I was really excited to see it because I love every port of this game I've ever played.

 

The cart is in great shape, and I'm glad to have it just from a collection perspective.

 

I popped it into my 7800, and it plays, but it screen jitters a little vertically, almost like it is having a slight problem with vertical hold, but then it keeps snapping back into place.

 

Any ideas what would be causing this? It's the only cart I've seen do this.

 

Thanks!

[Thomas Jentzsch]

The scanline count constantly changes between 261 and 262 scanlines. Probably that's causing your problem.

 

What kind of display are you using?

[troff]

Ahhh, that explains it. A known bug, then?

 

I'm using a modernish Samsung LCD. Still using RF input but direct in, no switchbox. I have it on my list to pick up on old CRT again. Will that likely work better?

 

Thanks!

[Thomas Jentzsch]

Probably, else more people would have reported.

 

I suppose that you LCD doesn't like even slightly out of spec video signals.

[alex_79]

I remember having issues (PAL color loss) with Tapper when trying the pal60 Hack by Omegamatrix. I think the original programmer tried to generate an interlaced display, but the timing was wrong.

http://atariage.com/forums/topic/193459-pal60-roms/page-6?do=findComment&comment=2872128

Edited December 16, 2016 by alex_79

[Thomas Jentzsch]

Maybe it would be worth a try to get that interlace mode enabled?

[reklen]

I have a 55 inch LED TV. Almost all the consoles run great, except for the N64 and the Atari 7800. If I hook up the Nintendo to the RF switch it works great. The 7800 won't do anything. The XE works great. The 2600 works great, except for my POPEYE cartridge, it plays, but the screen keeps scrolling up and down.Sounds like a similiar issue. I have a smaller 20 inch LCD TV, where the 7800 plays great, but the 2600 won't work, go figure.

[alex_79]

Maybe it would be worth a try to get that interlace mode enabled?

I tried it again and actually the original IS interlaced on my TV, even if the timing is off-spec:

 

This is a picture of the PAL60 hack from the link posted earlier, which had scanline count and VSYNC timing adjusted to have an atari-standard progressive 262 line signal. I turned down brightness to make scanlines more evident on camera:

 

This is a picture of the original NTSC version on the same TV with same settings (wrong colors, because the console and TV are PAL). Note that there aren't visible gaps between scanlines, because every other frame is shifted half scanline down. You can see a slight flicker by looking close at the screen, but obviously that doesn't show on camera.

 

The TV I'm using is quite tolerant regarding the timing of VSYNC to generate an interlaced signal. But older sets (like a 10" B&W one I have) are much more picky. So results with Tapper might vary depending on the TV set. (The uneven line count in different fields, for example, cause the spacing between scanlines to be different in that old TV, so that alignment between the fields isn't constant from top to bottom of the screen)

 

A while ago I did some experiments on the subject, using different TV sets and with a logic analyzer connected to the TIA outputs to monitor the exact timing of the SYNC signals depending on the cycle the register are strobed. I quickly lost interest, but maybe I'll take a look again and post the results in a new thread.

 

[Thomas Jentzsch]

How does it look?

 

All examples I have seen so far, looked worse than non-interlaced variants.

[alex_79]

It's worse, as the image is slightly flickering.
Since it doesn't take advantage of the extra resolution allowed by interlacing, the flicker isn't so bad (every pixel is at least 2 scanlines high, so at least a part of it is shown on every field), but for the same reason, there's no real point in interlacing in this case...