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Atari 7800 NTSC longhorn engineering 2.1b s-video mod


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I recently did the Atari 7800 longhorn engineering 2.1b s-video mod and am very pleased with it - for the Atari 2600 side.


The Atari 7800 side is not so good; I can't get a clean signal without disabling the tia-9 line first.

Even when I do, the composite is smudgy and the s-video is banded.


I've read on another thread that perhaps adding a resistor on this line may solve some of these issues?

However the in the end didn't end up so well.


Anyway, is with the switch on tia-9 as "good as it gets" with this mod for the Atari 7800 side?




Atari 7800 Joust... not great - this is s-video



Atari 2600, awesome!

Edited by slaanesh
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Like @mimo I also started out with the LHE mod. I didn't get the striping pattern like you show on 7800 games, but I did have horrible color bleeding and other issues. Even with the TIA-9 cut off switch installed, it still never look good on my TV. 


However, the LHE did look awesome on CRTs when I tested it that way. And I believe the LHE mod was originally designed for CRTs hence why that looked good. But as I use a modern display with all my gaming systems these days, I took it out and eventually put the UAV into it and never looked back!


Another option is to try and get one of Magic Knight's s-video only out mod boards. It will require tweaking the pots on it for your particular display but it produces really good s-video results as well. It doesn't have composite so you would have to get an s-video to composite adapter if you went that route, but I doesn't look that great using one of those adapters from my experience though it does work.


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Thanks for your replies!

That's pretty disappointing re: Longhorn AV mod.


Being in Australia, my natural video system is PAL 50hz. Whilst I like PAL, I'm not a fan of 50hz games.

So I wanted to go the NTSC route - despite all my games/equipment being PAL.


Getting hold of an NTSC Atari 7800 wasn't easy to do economically but I finally bought via eBay.


Anyway, I've removed some components to do the Longhorn mod; is it a matter of just replacing the Longhorn board with the UAV board?

Would any components need to be put back?


I suppose I can see what's involved with the UAV mod and work that out pretty easily :) just thinking out loud really.


Edited by slaanesh
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If you don't plan to use the RF ever again, then you can leave most of the components you removed from the LHE mod off I believe. The UAV and Magic Knight boards attach to the points just before those resistors you removed come into play. But the LHE instructions were never correct on the audio as it told you to attach your audio wire to the bottom of the R5 and R6 resistors. This is incorrect and will result in very low volume to almost no Pokey audio being heard compared to the TIA. Instead, you need to desolder the legs of those resistors off the board nearest the back of the 7800 or North legs as I call them and attach the audio wire to those legs attached together instead. 


You would be required to put the 74 logic inverter chip back in that you removed in favor of the LHE mod. That is required for the video output to work properly period.



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I don't plan on using RF ever again as i've removed it. And the AV mod is the entire point of this anyway :)

Anyway I should mention that in my first post, the s-video screen shots of Joust had the TIA-9 line disabled.


And I don't have the 75 logic inverter chip anymore. Also gone.


I'll make the fix for the audio... and leave this Atari "as-is". 


Looks like it's time to get another NTSC Atari 7800 via eBay and the UAV board :)

Edited by slaanesh
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The inverter is required so you would have to get that replaced. I think I found one laying around in my scraps when it came time to remove my LHE in favor of the UAV.


As for the RF being removed..etc. I like to keep it in place when possible. Because you have another means to connect to something should you want or need to. And with these AV mods in place, you can output the video to multiple displays at once if you choose. In my case, I can output via RF to one display or CRT, composite to another, and s-video to a third. It might not be needed for home use, but when I was hosting my own convention here locally, it was handy to have this ability so that people could see what the person was playing without being hovered over them. Also good for use in comparisons and testing video lag when I was going through my AV setup in my game room sometime back.


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I have the LHE mod in my later model 7800 and... it kinda sucks frankly. The fact that you need to wire up a switch to disable the TIA's chroma output to get clean 7800 video is bad enough, but in my experience the 2600 output was lackluster and full of bizarre interference. 


Personally I'm waiting for Tim Worthington's 7800RGB to show up at this point (he is actively working on it again BTW!). My 2600, 5200 and 800XL all now have RGB mods so the 7800 is the odd one out.

Edited by ApolloBoy
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I wish I'd researched my choice of AV mod before getting the longhorn mod... It was probably a year ago when I got it and only just got around to getting an NTSC Atari 7800 a week ago.


Anyway I find the 2600 side is excellent - see my first post. But the lack of 7800 support/quality makes it very disappointing overall.


@ApolloBoyI've considered the Tim Worthington's 2600RGB mod but if there is an 7800RGB mod that would be totally awesome; possibly worth the wait!

Do you have any info about it?

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All I would say is don't expect the MK or UAV mods to be totally clean on the 7800 side (done both to two seperate PAL 7800s), it's better, but it's far from perfect. Personally I'm waiting to see if Tim manages to pull off the 7800 RGB mod. I love the console, but it's easily the worst picture of all of the ones I own.

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  • 2 years later...

Okay so a few years later I revisited this mod and looked at what I had done. I re-soldered most points as my soldering skills have improved considerably since.

i then reviewed the installation documentation... I had made a mistake!

OMG! I had mistakenly soldered the wires that are at R18 and R19 to R18 and R17 respectively!

Do I feel foolish!

My excuse is that I must have assumed the wires go on the place where the resistors were removed!


The video quality is excellent with s-video!

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That does look pretty good. I've got an old Longhorn Engineering that I never installed, as I eventually went with a UAV mod instead.  But I've been thinking that perhaps it might be worth the effort to install it in a different 7800.  After seeing your images, maybe I will.


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