18 replies to this topic

[Clock]

I am just attempting to convert my 7800 PAL unit to work on SVHS using the circuit which is linked from the ATARIAGE FAQ page... but after building the board I then went and looked inside my ATARI

Yeah I know a bit stupid, I should have looked first

Anyway my unit looks nothing like the photos on the website

My 7800 is a PAL unit made in China and it has no expansion slot or any sign of one on the circuit board.

HELP ME.....Does anyone know of other websites (other than the 2 found from the FAQ page) that may help me.... I am doing this project right now, so a quick reply is most appreciated.

Thanks

[Clock]

I am going to try this, from a german site

http://www.retrobrot.tk/

It looks the same and lets hope the other circuit suits, if not then I am the owner of a melted doorstop and atariless

stop me immediatly if you know otherwise, cos I am soldering right now.

wish me luck

[Mitch]

The PAL 7800's have the parts in different places. Check this thread for more info.

Mitch
http://atari7800.atari.org

[CPUWIZ]

Your positions are exactly what the German instructions say as well.

http://134.155.59.2/...d/a7800mod.html

[Mitch]

CPUWIZ said:

Your positions are exactly what the German instructions say as well.

http://134.155.59.2/...d/a7800mod.html

Hmm, that's not too suprising considering that he's using my drawing.

Mitch
http://atari7800.atari.org

[Clock]

Yeah their both the same, but it hasn't worked, it nearly works though.

I think the sync is wrong as I can just make out asteroids but the screen is diagonally rolling. I used the alternative diode 2N3904 which is a rectifier diode and not a signal diode. I will purchase an signal diode and see what happens.

If it works I will email the website and explain that the alternative doesn't work. I hope this is going to work as I can then integrate my Atari into my Home Cinema set up.

I just also want to say that you guys are a great help and this must be the best forum I have ever stumbled accross..... yeah I think I will stay a while.

[Mitch]

I'm guessing the problem is because that mod isn't using a signal amplifier. If you check the mods listed in the 7800 FAQ, you will see that they both use a small amplifier circuit. Some TV's will work with the weaker signal and others won't. Apparently yours needs the stronger signal. Try running your connection through a VCR and see if that fixes it.

Mitch
http://atari7800.atari.org

[ZylonBane]

Clock said:

I am just attempting to convert my 7800 PAL unit to work on SVHS

You mean S-Video. SVHS is a type of VHS VCR with enhanced resolution.

[CPUWIZ]

Everyone but you knew what he meant.

[ZylonBane]

Obviously I knew what he meant, otherwise I wouldn't have been able to correct him.

[jsoper]

You know, I came across a great article on Usenet about the whole s-video/svhs confusion, it had a lot of good technical info. I'll include it when I launch my first webpage in a week or two. There's a lot of great projects I've been keeping secret lately.

And to get on topic: You can always trace the signals from the TIA pins themselves and find out where they go. I always start a video mod with just sync and one luma and see if that works first.

[Clock]

[quote]Try running your connection through a VCR and see if that fixes it. [/quote]


But I don't have a VCR... only DVD. I have tried connecting the S-video cable direct to the TV (GRUNDIG E72-911-the one designed by the Porche car co.) and also through a A/V amp (DENON AVR-3802) but the results are basically the same.

I tried touching the contacts on the new board to see if any resistance variables would make a difference and the picture did jump slightly differently.

There are 2 main reasons I wanted to complete this modification.
#1 to integrate it into my home cinema
#2 the R/F varies slightly and I have to fine tune the TV every time I use it.


[/quote]

[Mitch]

Clock said:

Quote

Try running your connection through a VCR and see if that fixes it.

But I don't have a VCR... only DVD. I have tried connecting the S-video cable direct to the TV (GRUNDIG E72-911-the one designed by the Porche car co.) and also through a A/V amp (DENON AVR-3802) but the results are basically the same.

I tried touching the contacts on the new board to see if any resistance variables would make a difference and the picture did jump slightly differently.

There are 2 main reasons I wanted to complete this modification.
#1 to integrate it into my home cinema
#2 the R/F varies slightly and I have to fine tune the TV every time I use it.

Hmm, well I know here in the US you can buy a standalone video amp for around $15-$20. You may check around and see if you can get one.

Mitch
http://atari7800.atari.org

[Clock]

OK I realise that nobody is probably interested, but just in case they are, I have now replace the offending diode with the proper signal diode, and guess what? .....It still don't work.

So unless someone helpfull can help me, my 7800 will not be permantly enjoying space in my living room.

The bit that worries me is that I used the circuit from the NTSC m/c and soldered it to the German Pal m/c points.... but look at that German site, It's full of variable resisters, where as I only have one in this circuit.

[Mitch]

A couple questions. Does the sound work? Do you have the problem on both 2600 and 7800 games? Which circuit did you end up using?

Mitch

[Edit_5]

CPUWIZ said:

Your positions are exactly what the German instructions say as well.

http://134.155.59.2/...d/a7800mod.html

This looks very interesting, shame I don't understand German, I'll run it through altavista later, thanks for the link WIZ

[Clock]

Quote

A couple questions. Does the sound work? Do you have the problem on both 2600 and 7800 games? Which circuit did you end up using?  

I didn't wire the sound up as the circuit does not give resister values in the sound section, only capacitor values. - I was going to try variable resisters until I found a happy result

It doesn't matter what game format I tried, I got the same result

I used the circuit found from the faq which was designed to be used on an NTSC m/c but I have a PAL, so hooked up to the positions shown from the German site, which uses an entirely different circuit by the looks of it.

I think it should still work, and I sort of make out images amongst the rolling/jumping image - so I know it's close.....so damn close.

I do hope you can help - or anybody.... please help me.

[Mitch]

Hmm, I don't have a PAL 7800 open at the moment, but does your 7800 have spots for audio and video on the board? If so, try hooking up the sync to the video spot.

Also, the audio doen't need a resistor just run it through the cap.

Mitch

[Clock]

I do not know what you mean by video spots on the board.

I just hooked and soldered onto the resister legs.

If I get the picture working then I will hook up the sound, there is no point otherwise.

I've also got another 7800 coming off ebay, just in case my fiddling breaks this one terminally. So I can take some risks now.