Weird interference on video

[idah0]

Hi,

I just got my Famicom from japan and finished the AV Mod.
It was CPU-07 so it was quite successful, minor jailbars still persist (working on it  )

The thing IS... every now and then when I'm playing for ex. Super Mario Bros I have this weird black line (like a tear) in the middle of the screen.
It just appears for a split second and disappears. It happens every few minutes or so, like 2 frames were incorrectly merged.
I'm using a CRT not an LCD, haven't tried it yet on the latter.

Have any of you encountered issue like that?

[famiac]

Loose/cold solder joint maybe?

Have you replaced capacitors on the main or power boards?

What kind of AC adapter are you using?

[FAMICOM_87]

show some pictures

[idah0]

Thanks for replies
Really hard to take a picture because it lasts only for a split second, I'll check the soldering.

I changed capacitors on the power daughterboard only, the one on motherboard looked OK and I was low on parts. I'll check it out again.

I got a 9V switching PSU I use for my Master System. There are no issues there, so it might not be it.

[jpx72]

This has been talked here before, it's something to do with Super Mario program, try to search forums.

[P]

Yeah that tear-like glitch line is a known bug in Super Mario Bros, there is probably no relation to your Famicom or AV-mod.

It only happens on NTSC PPUs, not on PAL or VS System PPUs.

[idah0]

Thanks for help,
That will put my mind at ease 
Never crossed my mind it might actually be the game, because of the state in which i got my famicom.

[P]

I remember being puzzled about it as well when I first got a Famicom as I didn't remember it from back in the day with my PAL NES. Since it showed up on all Famicoms I tried it on I figured it had to be SMB-related.

It doesn't happen in VS Super Mario Bros probably because of the differences in the RGB PPU. But the bug is still present in the game if you somehow run it on an NTSC Famicom/NES. I guess it will also not be present on other systems like the Famicom Titler that also has the RGB PPU.

Apparently some other games like Zelda 1, 2 and Paluthena has the same bug when scrolling horizontally, but not as regularly as in SMB.

For anyone interested in the bug, I think the answer is hiding in the Nesdev thread I linked to.