low-serial AES : noise in plain colors, and random black screens with OSSC

Boomchild

Timid Neo Newbie
Joined
Sep 9, 2022
Posts
1
Hi everyone !

I've registered here hoping someone will be able to help me to get the best signal out of a very early AES (5635) I just bought.

When I got it, it had a bad RGB signal, with checkerboard pattern scrolling left then right. I changed on my scart cable the Sync Pin to Pin7 instead of 3, and also replaced the 100uF capacitors by 470uF ones, with no luck.

Plus, with my OSSC, my TV (LG OLED C9) goes dark randomly (OSSC led stays green though, so it seems it's not losing sync), while with the same settings on my RGB-fixed AES 3-6 the picture is perfect and the screen never goes dark. Switching to Line 5x seems to make this problem disappear though, but still it doesn't make sense that the two behave differently.

I've then decided to do a RGB Bypass to see if composite is the culprit, but since tutorials for 3-1 revisions are nowhere to be found on the internet, it took me a while to find what to do. I still managed to do it by looking at the schematics and now the checkerboard pattern is gone, victory !

Well... sort of victory ? Now when looking at plain colors (not full black or full white), there is some sort of "noise". I don't know if my scart cable is an original one (I don't think so), maybe it is the culprit in there. When I look at my board, it has a capacitor soldered on a resistor, and I can't find it on other boards pictures online. I know from the seller who bought it new that it was sent to SNK/Guillemot for repair, maybe this was added then ?

Here are some pictures of the board (pics have been taken after the cap replacement, and before the RGB bypass) :








I hope someone will be able to help me getting rid of this noise, and more importantly of the screen randomly going black as if the game was changing resolution (it is not). I've tried KOF95, Super Sidekicks 2 and Magician Lord (all original) and got this problem with all of them.

Thank you !
 

Neo Alec

King of Spammers
20 Year Member
Joined
Dec 7, 2000
Posts
10,127
It makes total sense that the two behave differently. The original model AES has a 24MHz crystal for the video output, so the refresh is less compatible with TV's, unless yours has the daughterboard factory mod that was done to some. Check what refresh rate is displayed on the OSSC, and you should see a pretty big difference between the two. This would explain the signal drop outs.

How bad is the noise on solid colors? This too is normal with all analog RGB signals, however I have noticed that for whatever reason it is much worse with the slower refresh of the MVS or that early AES. I remedied this on my MV-1C by swapping in a later model AES 24.16MHz crystal, but these don't seem to be available for sale. My 24.16MHz crystal came from a donor parts console.
 
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maki

Crossed Swords Squire
Joined
Jan 1, 2022
Posts
189
Congrats on getting this old beauty :)

This is a NEO-AES, not a 3-1, its the first revision one released, there is no "RGB mod" for it, just replacing the resistors and caps with the proper values.

Unless you have replaced all caps, there is no point in trying to figure out "where the noise comes from", console5 is the best place IMO if you're in the US and do not want to spent lots of time sourcing quality caps.

The black screen on the OSSC is very common, there is a whole thread about these problems:
 
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