Pal 7800 display issues

[YANDMAN]

Hi guys

 

I know something like this has been covered before but as nobody posted any pics im not sure if my issues are the same and also its different depending on what games i play.

 

Some games have almost like a graphical glitch on the left hand side of the screen and yet other titles namely Choplifter, Fatal run play without any screen glitch but are very fuzzy, Its nothing to do with tv type or tuning as i have tested it across four different crt's, The other thing is that when i play 2600 games on this 7800 they are perfect absolutely crystal clear.

 

When i initially purchased Ms.Pac man as this was the first time i saw this glitch i wondered whether i had been sold an NTSC copy now i dont know if it would even run but i had read that some NTSC games will run but with graphical issues, the other game i have heard this mentioned about is centipede and that was the second game i noticed it on.

 

I had pondered just buying another 7800 but thought somebody might know what this problem is, I have stripped the machine and cleaned the rf connection and it looks like new, The console itself is mint but i have also cleaned the cartridge slot and all the offending cartridges but with no change, I am awaiting delivery of a signal booster to see if that helps.

 

Ill include screen shots showing the glitch and a 2600 game with no issues at all.

 

Thanks in advance

 

Yan

[Mayhem]

Yeah, it's just an issue through RF, and there's not much you can do about it. My PAL 7800 does very similar. Which is why I generally just use my NTSC S-video modded 7800 instead.

[YANDMAN]

Oh really?? That sucks, So why does it only become affected by certain games then?? and why do some run o.k, ball blazer for instance is crystal clear no issues whatsoever as is food fight and galaga

 

Im gonna have to see about getting a friend to do an s-video mod for me in this case.

 

Thanks

[alex_79]

On PAL 7800, the clock signal coming from the TIA cause interference in 7800 mode, so maybe that's what you're experiencing. Here you can find a fix (see post #18 and #19).

 

I modded my 7800 using the "easier composite mod". While not as crisp as s-video, the output is quite good (at least on crt TVs) and much better than rf anyway. The mod is so simple that I didn't even need to use a perfboard to build it, I just soldered the components together and isolated them with heat-shrink tubing. I posted instructions for pal boards in this post if you are interested. (note that the description contains an error: you must desolder the LEFT ends of R33 and R32, as it's correctly shown in the picture).

 

Another way to improve the video output is to put a switch to enable only TIA or MARIA chroma output, but I can't find the thread where it was discussed.

[YANDMAN]

Wow thanks man thats really helpful, I might attempt this myself