Schmutzpuppe Posted October 3, 2004 Share Posted October 3, 2004 Hi folks, I searched the forum for a PAL video mod and found some threads about it but unfortunately not schematic or something. Finally I got stuck on this page http://134.155.48.202/~wi01196/colude/retrobrot/ The result didn’t satisfy me because I was unable to trim the potentiometer to the correct values so I had a too bright picture, missing colors and some interference. But at the end the page was very useful because it shows all necessary signals on the pal device. I made the following modifications to the given schematic: I replaced the trim potentiometers with some resistors: Lum0: 2,2k ohm Lum1: 1k ohm Lum2: 470 ohm Lum3: 220 ohm Tie all endings together and connect it to a 1K ohm trim poti (here you can adjust the total brightness). For the 2600 and 7800 Chroma output use a 10K poti instead of 1K and tie the end to a 1uF capacitor, For the Sync signal I used a 470 ohm (a smaller value seems to make no sense) and connect it to a 1K poti. If you put all together you have the composite video output. It’s a good idea to use ResQsoft (http://home.earthlink.net/~resqsoft/7800_mod.htm) circuit for audio it gives a good balance of internal and external audio. The result of the effort is a much better picture than RF. Maybe I will try a separate luma/chroma output but for now I am satisfy. One side note, I wonder about the used rom in my 7800, it’s an ordinary M27128 Eprom with a sticker (0.8.w/ASTRDS 7800TSC/PAL). Matthias Quote Link to comment Share on other sites More sharing options...
+Mitch Posted October 4, 2004 Share Posted October 4, 2004 Do you have a dump of that EPROM? I'm pretty sure mine said 1.0 w/ Asteroids, so maybe you have a different version than what's out there. Mitch Quote Link to comment Share on other sites More sharing options...
Schmutzpuppe Posted October 4, 2004 Author Share Posted October 4, 2004 Do you have a dump of that EPROM? I'm pretty sure mine said 1.0 w/ Asteroids, so maybe you have a different version than what's out there. Mitch Not yet but I could dump it (have to search my eprom burner in the cellar first). Quote Link to comment Share on other sites More sharing options...
+Mitch Posted October 4, 2004 Share Posted October 4, 2004 If you can find your EPROM burner that would be great. It would be nice to compare it to the later release and see if there are any changes. Mitch Quote Link to comment Share on other sites More sharing options...
Schmutzpuppe Posted January 14, 2005 Author Share Posted January 14, 2005 If you can find your EPROM burner that would be great. It would be nice to compare it to the later release and see if there are any changes. Mitch It took some time but I finally did it. The rom is attached but it is the same than the one I have on my HD so (unfortunatly) nothing new Maybe it is differend to the version you have... a7800p.zip Quote Link to comment Share on other sites More sharing options...
Schmutzpuppe Posted January 16, 2005 Author Share Posted January 16, 2005 Today I decided to modify the circuit for s-video. I have to say that I am very satisfied with it All I did was to build the mentioned circuit (I build it one more time for my other 7800) and don't put the luma and chroma signal together. Instead I used the luma circuit from Jay Tilton's Video Mod (http://home.earthlink.net/~resqsoft/). That's it, runs perfect. Here are before/after pictures: Quote Link to comment Share on other sites More sharing options...
Schmutzpuppe Posted January 16, 2005 Author Share Posted January 16, 2005 Btw. I captured the pictures with my tv-card, normal photography doesn’t look that good. Quote Link to comment Share on other sites More sharing options...
+Mitch Posted January 16, 2005 Share Posted January 16, 2005 Cool! It looks like you have a great picture. Incidentally, do you know who's site that is that you linked to in your first post? He used my ASCII PAL 7800 schematic with the A/V locations and didn't even give me credit. Mitch Quote Link to comment Share on other sites More sharing options...
Schmutzpuppe Posted January 16, 2005 Author Share Posted January 16, 2005 Cool! It looks like you have a great picture. Incidentally, do you know who's site that is that you linked to in your first post? He used my ASCII PAL 7800 schematic with the A/V locations and didn't even give me credit. Mitch Hi Mitch, I don't know the guy but you can mail him if you just press "kontakt" in the navigation (top right).. The ASCII schmatic was very helpful thanks! The mentioned site was the only place I found informations about the pal layout do you have some more links? Quote Link to comment Share on other sites More sharing options...
+Mitch Posted January 16, 2005 Share Posted January 16, 2005 Yeah, I noticed that but I wasn't sure how much English he understood so I didn't know if it would be worth emailing him. And, sorry, I'm not aware of any other PAL 7800 A/V mods. How much different is that one from the NTSC one? Mitch Quote Link to comment Share on other sites More sharing options...
CPUWIZ Posted January 16, 2005 Share Posted January 16, 2005 Yeah, I noticed that but I wasn't sure how much English he understood so I didn't know if it would be worth emailing him. Let me know if you want help with a translation. Quote Link to comment Share on other sites More sharing options...
Schmutzpuppe Posted January 16, 2005 Author Share Posted January 16, 2005 Yeah, I noticed that but I wasn't sure how much English he understood so I didn't know if it would be worth emailing him. Ok, didn't thought about that. I can mail him if you want. And, sorry, I'm not aware of any other PAL 7800 A/V mods. How much different is that one from the NTSC one? Mitch The one at the retrobrot site is quite different it just use potentiometer (no fixed value resistors, capacitors, etc.). The last one I did is basically the Jay Tilton mod. What I changed was the resistor values for Lum0-3 and I used a 470 resistor and a 1k poti for sync. Quote Link to comment Share on other sites More sharing options...
+Mitch Posted January 17, 2005 Share Posted January 17, 2005 Thanks guys, I may take one of you up on your offer when I decide what I'm going to email him. Mitch Quote Link to comment Share on other sites More sharing options...
SoundGammon Posted February 21, 2007 Share Posted February 21, 2007 Hey, How would it look if you were to try to remove all the 2600 video resistors and the chroma (2600) resistor, and make it a 7800 only video? You could try cutting just one side of each resistor and looking at the results and if it isn't any better, you could "spot" solder them back in. They might be "loading" the video 7800 down. Rob Quote Link to comment Share on other sites More sharing options...
OldAtAtari Posted July 6, 2018 Share Posted July 6, 2018 I know this is an old thread, but I wanted to add the link to the archived version of Jay Tilton's 7800 AV mod(the rest of his site is here as well): https://web.archive.org/web/20090119023846/http://home.earthlink.net:80/~resqsoft/ Quote Link to comment Share on other sites More sharing options...
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