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Modding French 7800 to composite?


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#1 tajume80 OFFLINE  

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Posted Mon Feb 11, 2019 3:26 PM

Hi!

I recently bought French 7800. Unfortunately the picture quality via scart is really bad. While playing 2600 games there is ugly thick "scanlines" and 7800 don't look good either. It seems my that the rgb board is either broken or just bad. I attached a photo where you can see the horizontal lines.

So I'm planning to mod the console, so I can use composite.

The problem is that the motherboard is slightly different than pal version.

Is there a way to mod the French version to composite?

Attached Thumbnails

  • photo_2019-01-08_23-17-09.jpg


#2 Mitch OFFLINE  

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Posted Mon Feb 11, 2019 3:47 PM

From the pic I would say you have a shielding issue, maybe a bad cable. Does the cable look original?

Mitch

#3 Rastignac OFFLINE  

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Posted Mon Feb 11, 2019 4:46 PM

Is there a way to mod the French version to composite?

Scart gives RGB + Composite + audio.
Some pins are the RGB ones, others are the composite ones.
TV set looks first for the RGB signal, then drops to composite signal if RGB is not found. So, removing/pushing RGB pins from the Scart forces composite output.
(There are also cheap "dongles" with Scart-in --> RCA-out).

#4 tajume80 OFFLINE  

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Posted Mon Feb 11, 2019 4:50 PM

From the pic I would say you have a shielding issue, maybe a bad cable. Does the cable look original?

Mitch


The cable is original and I've started to mod the console to composite and it shows the same problems as via scart. The problem with the mod at the moment is that the motherboard is different than the pal version, so I only managed to get black and white picture out of the motherboard. I suspect that I need to take out and add some resistors to the motherboard because of the differences between pal and secam versions.

#5 tajume80 OFFLINE  

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Posted Mon Feb 11, 2019 4:55 PM

Scart gives RGB + Composite + audio.
Some pins are the RGB ones, others are the composite ones.
TV set looks first for the RGB signal, then drops to composite signal if RGB is not found. So, removing/pushing RGB pins from the Scart forces composite output.
(There are also cheap "dongles" with Scart-in --> RCA-out).


Thanks for the advice, but in this case the picture quality from the rgb board (or the console itself) gives a really bad picture quality via rgb and via composite (I've started to mod the console to composite, but it only shows black and white colors). I mentioned in a new post that I suspect that I need to remove and insert some resistors, so I might get colors, and to get rid of the vertical lines. I'm also suspecting that the secam 7800 might also be broken.

#6 Mitch OFFLINE  

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Posted Mon Feb 11, 2019 8:39 PM

Can you post a pic of the system board?
By the way, there isn't a secam 7800, only PAL and NTSC.

Mitch

#7 tajume80 OFFLINE  

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Posted Tue Feb 12, 2019 2:33 AM

Can you post a pic of the system board?
By the way, there isn't a secam 7800, only PAL and NTSC.

Mitch


Ok, good to know! I didn't know about that fact it isn't secam.

The pictures aren't that great, but I'll take a better shot later. I've removed the rgb daughterboard and some of the resistors that have to be removed for the composite mod. The thing is that I need to know which resistors I have attach to the motherboard, as some of them are missing in the French version.

Attached Thumbnails

  • IMG_20190211_212343_1.jpg
  • IMG_20190211_212403.jpg

Edited by tajume80, Tue Feb 12, 2019 2:52 AM.


#8 Mitch OFFLINE  

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Posted Tue Feb 12, 2019 3:25 PM

That looks like the standard PAL 7800 board with the alt memory daughter board.

Mitch

#9 tajume80 OFFLINE  

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Posted Tue Feb 12, 2019 4:36 PM

Does anyone know what resistors I need to these areas which I have marked?

The French 7800 does not have them. I've removed some resistors needed to the composite mod. When compared to the regular pal version, it seems to have resistors in places which the French does not have. I guess I need them to complete the composite mod, because otherwise the picture is black and white. It might also affect the picture quality.

The other picture is from one of the mod tutorials I've found via Internet.

Attached Thumbnails

  • 1.jpg
  • 2.jpg


#10 Mitch OFFLINE  

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Posted Tue Feb 12, 2019 9:25 PM

I think this is the best that I have right now.

 

C300633.jpg



#11 slx ONLINE  

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Posted Sat Feb 16, 2019 2:34 AM

My French 7800 does not show colors in 2600 mode, any ideas on why/how to fix appreciated as well. Unfortunately these seem to be such rare beasts that next to nothing is on the web for them.

#12 Mitch OFFLINE  

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Posted Sat Feb 16, 2019 11:22 AM

Check the chroma connection on the 2600 side.

 

Mitch



#13 tajume80 OFFLINE  

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Posted Sat Feb 16, 2019 1:18 PM

Does anyone know anything about the resistor/transistor I've marked on the picture. You can find it on the regular pal motherboard, but not on the French version. I'm still wondering how to make the composite mod, I just have to know what parts I have to buy.

I'm starting to think that maybe I should just buy a 2600 Junior to play my Pal 2600 games, and play ntsc 7800 and 2600 on my ntsc 7800 because the French 7800 is either broken or just bad. Too bad for me, because the French 7800 wasn't cheap. Too bad about the really bad picture quality. I thought that having a scart version would have been the best version out there :D

Attached Thumbnails

  • Untitled-1.jpg

Edited by tajume80, Sat Feb 16, 2019 1:32 PM.


#14 mimo OFFLINE  

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Posted Wed Feb 20, 2019 5:37 AM

Have you tried a different TV? 
My French 7800 looks terrible on my LCD that displays s-video 8 bit consoles really nicely.

Looks fine on my Sony CRT though.

On my big plasma screen it displays terribly with the genuine peritel cable, but perfectly fine on the cable I made myself for my ST.



#15 tajume80 OFFLINE  

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Posted Yesterday, 5:50 AM

Have you tried a different TV? 
My French 7800 looks terrible on my LCD that displays s-video 8 bit consoles really nicely.
Looks fine on my Sony CRT though.
On my big plasma screen it displays terribly with the genuine peritel cable, but perfectly fine on the cable I made myself for my ST.


Yes, I've tried three different types of tv's: oled with framemeister, lcd and crt tv. Most surprising was the crt, as it looked as horrible as on modern tv sets.

I suspect that there is something wrong with the chips.

Maybe I should try it with the ST cable.

Edited by tajume80, Yesterday, 6:35 AM.





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