Background Tiles are wrong

[P]

My friend has an AV-modded Famicom, it worked for years before but now all BG tiles are wrong in Rockman (and any other games we tested including my Everdrive which has super clean pins). Sprites are fine.

We have tried sandpapering the cart slot without any improvement.
Since the tiles are the same every time the cart is inserted I wonder if the problem is more serious.

[fredJ]

Yes I think it could be more serious but I don't know what it could be.
Could be a trace on the board that is damaged or a chip that is defect. Maybe a RAM chip.

[80sFREAK]

How about Family Basic?

I can guess for degrading soldering, CIRAM or '373 failure, but it's just a guess.

[P]

He doesn't have Family Basic, I suppose I could test it with my Everdrive but I don't have my Family Keyboard here at the moment.

I will open it and take a look next time I'm around.