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Got my 7800 modded - can’t say enough nice about Crossbow!


gorfcadet

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I'll hyperlink the gif below; can you see it now?

 

YIQ-7800-warmup.gif

 

Nope...hehe

 

BTW I guess now would be a good time to mention that I was diagnosed with colorblindness when I was in the service? The only difference I can physically see with my eyes on those screen shots are on column E about 2/3 the way down on the sky/light blue colors as those appear to get more teal from left to right. The rest pretty much look the same from shot to shot. So I will take your word for it.

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BTW I guess now would be a good time to mention that I was diagnosed with colorblindness when I was in the service? The only difference I can physically see with my eyes on those screen shots are on column E about 2/3 the way down on the sky/light blue colors as those appear to get more teal from left to right. The rest pretty much look the same from shot to shot. So I will take your word for it.

Thank you for your service, sir. It is very much appreciated. :thumbsup: :)

 

The quest for color 'accuracy' is just a tad bit nurturing of my *cough*borderline*cough* OCD. ;)

 

Regardless, UAV is still the best mod currently available for the 7800. Lucky folk, all those who are having, or had it, installed.

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THAT was fast! All I have left is 1 more UAV but it is the complete kit for use in a 5200 or other atari 8-bit computer and I might be claimed for use in an Atari 400.

Edited by -^Cro§Bow^-
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Does the picture quality wind up looking better than using a VCR as a demodulator?

 

My experience has been it is a two-part factor: 1) The console build quality 2) Quality of the mod.

 

That being stated, even with the more underwhelming system mods I've witness, it is still better than passing the signal through a VCR. However, I have yet to see the cheapest mod with the cheapest console build. The presumption is though, it would likely render a picture quality comparable to the VCR pass-thru option.

 

In light of the above, if you choose to go with a mod, the odds are at worst it will be as good as utilizing the RF thru a VCR. At best, you'll experience (near) S-Video quality. Going with the Longhorn Engineer Mod, or even better the UAV mod discussed in this thread, it will probably result in leaning closer to the latter than the former.

 

Still, there is no sure thing/guarantee when dealing with used ~30 year old hardware, so of course ultimately, YMMV.

 

*EDIT: Bryan's research in conjunction with the UAV for the 7800 is impressive. Some of it is mentioned in this post. It is reiterated in the spoiler below for convenience.

 

 

During a 7800 game:

 

A 5.7K path to 5V is always present. When Maria color is driven high this is paralled with a 4.3K path to 5V, so we get an effective path of 2.534K. The voltage becomes 0.78V (470/2534)*5

 

When Maria color is driven low, we can combine the 4.3K with the 470 for a parallel resistance of 424 ohms. This yields 0.35V. (424/6124)*5

 

So, the chroma signals are close in amplitude (0.38V vs 0.43V) even though one has a DC offset (until it reaches the cap).

 

In 2600 mode, Maria's pin will always read as a logic 0 because TIA won't drive it higher than 0.38V.

 

In 7800 mode, TIA's pin will always read high because of the local 1K pull-up.

 

In order to combine a normally high and a normally low signal, you need to invert one, or use an exclusive-OR (XOR) gate.

 

Getting back to UAV...

 

UAV uses an XOR gate to provide the artifact inversion feature. If you put Maria Color into the normal color input and connect TIA Color to the invert pin in the configuration header, you should get both color signals combined.

 

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get a beater unit to mod and keep the pristine one

 

Exactly!!!

 

I pretty much only AV mod or really only mod the consoles I'm actually going to use a lot and want the convenience of having everything connected to one display as much as possible. Because of that, my really nice and pristine consoles are kept in their boxes and rarely used to be honest. But that is the collector in me. If you only have one 7800 for use and it looks pristine, then there are still ways to do this mod that don't require cutting holes in the case. But then you have to be okay with connectors hanging off wires that come out through openings already in the case. It would look ugly, but you wouldn't have to modify the case at all doing this. Sure the console is modified inside, but that is what I like about the UAV. You don't have to really remove anything from the system. Worst thing you have to do is cut the audio resistors going into the RF modulator section to get your audio. But you don't have to remove them you just cut them and attach the audio out from the ends you cut. So it is pretty easy to reverse the process of everything in the future if you wanted to.

 

Other mods in the past required the removal of components from the main pcb to provide the best results. Bryan got around all of this by taking the signals and putting them through his own encoder circuit to bypass the need to remove anything off the system. Very clean and elegant and I'm sure he spent more time than he will ever admit to research it for the rest of us.

Edited by -^Cro§Bow^-
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So many things to ask and comment on...

 

*So with this particular mod, the 7800 power supply connector remains but now there's a Genesis plug as well? Is that correct? Is there a switch or something? If not, if both are plugged in at the same, wouldn't it blow?

 

*Isn't the ultimate test of 7800 graphics modding is playing Tower Toppler on both a CRT and an LCD to see if he becomes black & white?

 

*Any onboard POKEY modding? I remember someone doing that in the MarketPlace and I think someone is doing it on Facebook.

 

*I wonder if a UAV and a hypothetical RGB mod could be done to the same motherboard. Probably not.

 

*I know all about the Genesis' terrible Composite output. My Sony Bravia prefers my 7800 connected to the antenna port over the Composite Genesis connection...other than the RF signal noise, it's a much clearer picture. Then again, the same Sony doesn't really like my 5200 but a cheapo Best Buy Insignia 19" does.

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So many things to ask and comment on...

 

*So with this particular mod, the 7800 power supply connector remains but now there's a Genesis plug as well? Is that correct? Is there a switch or something? If not, if both are plugged in at the same, wouldn't it blow?

 

*Isn't the ultimate test of 7800 graphics modding is playing Tower Toppler on both a CRT and an LCD to see if he becomes black & white?

 

*Any onboard POKEY modding? I remember someone doing that in the MarketPlace and I think someone is doing it on Facebook.

 

*I wonder if a UAV and a hypothetical RGB mod could be done to the same motherboard. Probably not.

 

*I know all about the Genesis' terrible Composite output. My Sony Bravia prefers my 7800 connected to the antenna port over the Composite Genesis connection...other than the RF signal noise, it's a much clearer picture. Then again, the same Sony doesn't really like my 5200 but a cheapo Best Buy Insignia 19" does.

 

The Genesis plug is just that. It is an extra barrel jack attached off the same points as the original power plug. As for both being plugged in at the same time, you will still only be providing 9 volts more or less regardless but the current would be crazy, still the regulator will only use what ever current it needs from the supplies. But honestly why would you plug them both in? It really is only for a this or that use.

 

Tower Toppler is still basically a black n white looking game in S-video. In composite with the UAV it doesn't look right at all color palate wise. Not sure what's up, but instead of a grey or blue colored tower at the beginning it is pretty much brown or burnt orange. However, the bonus rounds looks correct as does all other games I've tried. There are still issues with the gold hues but all the Mods suffer this and it is more a result of how the LCD interprets the color as on a CRT the UAV looks correct. But still not quite right with Tower Toppler as that one is just odd. But only one game and still playable and looks okay otherwise.

 

I don't mod the Pokey. What I do is take the audio after the R5 and R6 resistors before their filter caps to the RF modulator section. You tie the two resistors together, attach a new 10uf 16v or greater cap for additional DC filtering and then run that out to your audio RCA. This will result in properly mixed TIA and POKEY audio. I've heard of others that like to wire in Stereo directly from the TIA and then run the POKEY into one of the channels, but I'm not a fan of it myself and prefer to keep the audio pretty much as it was originally in the schematics just cleaned up a bit without the rest of the RF circuit in the way causing noise all over it.

 

The UAV doesn't require any actual components to be removed so you an keep the system fairly stock. I haven't looked at any of the RGB mods that are out there for the Atari systems, but they likely require removing components similar to the previous AV mods. Even then the UAV pretty much takes its signals before any of the main components to it wouldn't likely be an issue if you removed resistors off the video ladder that the UAV taps into since again, the video for the UAV is taken before the resistors.

 

Does that help at all?

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*Any onboard POKEY modding? I remember someone doing that in the MarketPlace and I think someone is doing it on Facebook.

 

I don't mod the Pokey. What I do is take the audio after the R5 and R6 resistors before their filter caps to the RF modulator section. You tie the two resistors together, attach a new 10uf 16v or greater cap for additional DC filtering and then run that out to your audio RCA. This will result in properly mixed TIA and POKEY audio. I've heard of others that like to wire in Stereo directly from the TIA and then run the POKEY into one of the channels, but I'm not a fan of it myself and prefer to keep the audio pretty much as it was originally in the schematics just cleaned up a bit without the rest of the RF circuit in the way causing noise all over it.

 

Bryan does mention an AC (Audio Companion) Board to complement the UAV. If interested, there are step by step instructions and detailed pictures from his blog post respecting it.

 

Well deserved kudos prior to it regarding -^Cro§Bow^-'s excellent coverage and guides on the UAV.

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Bryan does mention an AC (Audio Companion) Board to complement the UAV. If interested, there are step by step instructions and detailed pictures from his blog post respecting it.

 

 

Sadly Bryan doesn't have any more UACs available and advised me he wasn't planning on making anymore as they were a right royal pita to make. I don't doubt it given has incredibly tiny they are! I'm hoping and I believe Bryan stated he is thinking of incorporating the UAC into the UAV which does make sense but just have to see.

 

For any insterested...here is 7800 #2 since Friday with all the board work done to it. New caps, new panel buttons, audio modification done and ready to be connected, and the UAV is installed and mounted to the board. I'm waiting on more av parts to come in over the next couple days to finish this one up and get it back on its way. Trying to get them knocked out so I don't have them pile up on me LOL.

 

post-6-0-75083700-1528771308_thumb.jpg

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Wanted to mention some things I was advised to change regardling this last one I posted up here. So I was trying to keep the kynar wires tidy but have been informed that my placing them under the axial caps and resistors is bad form. So I pulled them all out and just applied some shrink around them instead but no longer under the components. I know there is risk of cross talk in doing that, but honestly it didn't look any different before or after. Also, C64 in the center right was clipped as I found it was preventing any of the starpath games from loading up and also prevented Darrel's bus stuffing demos from working at all. Seems to only break 2600 dark chambers in clipping it so...customer is fine with that.

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Gotta give a huge shout out for Crossbow! Just got back the 7800 that he installed a UVA in and recapped for me. He is a pro and totally fixed some other issues I was also having with it! The UVA is so much cleaner than the older shvs modded 7800 I have. Pitfall never looked sooo good! THANK YOU!! icon_thumbsup.gificon_thumbsup.gif

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THANK YOU!! icon_thumbsup.gificon_thumbsup.gif

You are most welcome! I do find it interesting that the fix to your harmony cart and some other issues, was to use the same fix that allows the supercharger to work. Clipping C64 only sacrifices the 2600 version of Dark Chambers but allowed this 7800 to finally run all the bus-stuffing demos and the supercharger roms from a Harmony. It wouldn't even run fixed roms off my harmony until I clipped that cap. Oh well...this is very much a case of the needs of the many outweigh the needs of the few (Or in this case, the one game...).
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  • 2 weeks later...

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