30 replies to this topic

[MGA2009]

Hi.

This is my first post. I have an Atari 7800 PAL B and I'm looking to get the best picture of it.

After reading lot's af post I could like to know If I'm in the right direction as I'm no pro and all link to the schemes links were broken.


After knowing the correct "points" is it OK to follow with the luma scheme I found?


Then the chroma...


And finally If I want composite out I just attach chroma and luma together and with it to the RCA connector and If I want s-video I just follow this scheme:


Any suggestions or modifications you would suggest for a PAL mod?

What kind of video upgrade compared to RF modulator connection?

Ohh and all the credits to the people who made the schemes and found the points, kudos to them.

Best Regards.

Edited by MGA2009, Tue Dec 14, 2010 9:37 AM.

[Rybags]

Same as my 3.

I was going to try something of a mix of the best of a couple of the ones around but never got around to it.

Not exactly an expert on electronics either so that doesn't help.

I've been burnt before trying NTSC-centric mods on my PAL 800XL, so you can't necessarily say that what's good for one video standard or particular motherboard revision is going to work well for others.

I suppose the best approach would be to build a proto first and do minimal modifications to the motherboard in such a way that anything can be backed out if needed.

[MGA2009]

Rybags, on Tue Dec 14, 2010 9:29 AM, said:

Same as my 3.

I was going to try something of a mix of the best of a couple of the ones around but never got around to it.

Not exactly an expert on electronics either so that doesn't help.

I've been burnt before trying NTSC-centric mods on my PAL 800XL, so you can't necessarily say that what's good for one video standard or particular motherboard revision is going to work well for others.

I suppose the best approach would be to build a proto first and do minimal modifications to the motherboard in such a way that anything can be backed out if needed.

Hey, thanks for your answer.

I don't think we need to be experts to "make" the modification, probably need to be experts to figure out how to do it the first time... You seem to be a member since a long time ago, so let me know If I missed an important post for 7800 PAL modifications.

I have a PROTO which is basically a composite out on my 7800 PAL but it's not giving me a "crisp" picture... I did it with only (1) 220uF cap and (1) 750ohm resistance. So probably with a more efficient circuit a using separated LUMA / CHROMA we might get a "super crisp" picture.

Best Regards.

[mamejay]

Hello Everyone,

I too have just got myself a PAL 7800 which I want to AV mod.
I have build a strip board diagram to build the circuit from. I have attached it to make it easier if you want to build one yourself.

It is exactly the same as your attached schematic except for I have set resisters for R5 and R6 instead of the 10K pots. You can add the pots instead if you like.

Can someone with a bit more experience in circuit board making have a check over this and let me know if they think I have designed it correctly?

Attached Thumbnails

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[MGA2009]

Niiice!!

Thanks for that awesome scheme.

I'll definitely put it to work.

Do you know what kind of picture can we expect from that video out mod?

Best Regards.

mamejay, on Thu Dec 16, 2010 4:54 PM, said:

Hello Everyone,

I too have just got myself a PAL 7800 which I want to AV mod.
I have build a strip board diagram to build the circuit from. I have attached it to make it easier if you want to build one yourself.

It is exactly the same as your attached schematic except for I have set resisters for R5 and R6 instead of the 10K pots. You can add the pots instead if you like.

Can someone with a bit more experience in circuit board making have a check over this and let me know if they think I have designed it correctly?

[mamejay]

I could not get this mod working on the PAL 7800. i suspect that the resistance values need to be tweaked to get the correct picture.
I found this video on youtube. Its only for a composite mod but the quality looked pretty good.

I have drawn up a board if you wanna make the circuit. Really easy and small.

Just be careful when working on the 7800 that you unplug the console and hit the power button to discharge it. I did not do this and my soldering iron shorted something out and now i have problems with my console.

Attached Thumbnails

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[MGA2009]

mamejay, on Sun Dec 19, 2010 5:26 PM, said:

I could not get this mod working on the PAL 7800. i suspect that the resistance values need to be tweaked to get the correct picture.
I found this video on youtube. Its only for a composite mod but the quality looked pretty good.

I have drawn up a board if you wanna make the circuit. Really easy and small.

Just be careful when working on the 7800 that you unplug the console and hit the power button to discharge it. I did not do this and my soldering iron shorted something out and now i have problems with my console.

Thanks for the second scheme... but I already have composite OUT and I think it would be nicer to get separate luma / chroma...

You say you tried you first scheme and also the one I posted and none worked?

[mamejay]

The second one works perfectly but there was some static that has affected one of the chips on the 7800. This was my fault for not discharging the motherboard.

[mamejay]

Got it working tonight. Look very sharp!! I used variable resistor pots and adjusted till it looked right.

I will post up the values soon.

[mimo]

mamejay, on Tue Jan 18, 2011 4:36 AM, said:

Got it working tonight. Look very sharp!! I used variable resistor pots and adjusted till it looked right.

I will post up the values soon.

great stuff, I am going to try this on a 400 at some point soon

[mamejay]

BTW,

The 26000 Chroma pin mentioned in the picture is incorrect. I had to find another point to grab the Chroma signal. You can get it from the next row of resistors next to the Audio outputs. about the 3rd one down.

[mimo]

someone pointed me to this one. Not tried it yet, looking for a suitable victim
http://translate.goo...VAcs_Pc8dNHpTbA

[mamejay]

That is the same circuit I posted above.
I have tried both that mod and the S-Video mod. S-video provides much better results than the composite circuit.
I have also converted the S-video to composite and get better video than that circuit you mentioned.

[mimo]

Thanks, do you have a link to the s-video mod that you did?
I really want to mod a PAL 7800

[mamejay]

Try this one. It exactly what the schematic above is.

Attached Thumbnails

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Edited by mamejay, Tue Feb 15, 2011 4:32 AM.

[mimo]

Thanks, I guess D1 is a diode of any size?

[mamejay]

Correct.
Also the 2 x 10K resistors on the chroma lines should be trimpots just so you can get the colour just right.

[mimo]

mamejay, on Tue Feb 15, 2011 5:48 AM, said:

Correct.
Also the 2 x 10K resistors on the chroma lines should be trimpots just so you can get the colour just right.

many thanks, not sure when I will have time to do this, but I definitely will

[NeilTheDruid]

Quick question. Would a 2n2222 be an ok substitute for the 2n3904? I've got some 2n2222's lying around, it's not a problem if I have to get some 2n3904s though.

[Underball]

NeilTheDruid, on Tue Apr 19, 2011 1:56 PM, said:

Quick question. Would a 2n2222 be an ok substitute for the 2n3904? I've got some 2n2222's lying around, it's not a problem if I have to get some 2n3904s though.

Yes. They will function the same way in this circuit.

[NeilTheDruid]

I've just finished building this mod using the schematic in post #15. Unfortunately, I'm having some problems getting a picture. At the moment the picture flicks between black and white "snow", but every now and then the picture stops on a crystal clear picture of the game. Any ideas for trouble shooting? I've already checked that the circuit is receiving 5v. Cheers!

[mimo]

what type of tv are you using? can you try on a different one?

[NeilTheDruid]

The TV I'm using is a sony bravia KDL model I think - I'd have to check for the exact model. Unfortunately, I don't have another TV to try.

[NeilTheDruid]

I am still playing around with this on my rev C. I found I had to move the Luma0 connection over one resistor to the left because the Luma0 line on the TIA didn't have any connection with the point above. With the other luma and sync points where they are on the photo above I get black and white rolling, with some occasional stops on a clear picture. I tried moving Sync and Luma1,2,3 to the other side of the resistors and actually got a steady picture but the brightness was way down and not really useable.

Looks like I may have to find the points I need myself. When I am looking for the correct points, what am I looking for aside from continuity from the correct pins on the MARIA and TIA?

[mamejay]

I got the same issue when doing mine with a dark image.
i pulled everything out and started again.
The second time it just worked perfectly. Not sure about what advise I can give.

As for the points on the TIA and Maria you just need continuity direct to the TIA and Maria.


BTW have you tried on any other TV to see if you get a better picture?