NES toploader garbled graphics

I bought a toploader for 10$ at a flea market over the weekend. The seller didn't know whether it worked or not so I took the chance. When I got home and turned it on, it only displays garbled graphics ie, characters in place of sprites,etc. After doing a bit of research, I haven't really come up with too much except that it may need a good cleaning(which i did) or the ppu may be bad. If it is the ppu, I am thinking I can just drop one in from an NES front loader that wont turn on. As far as I know, the ppu on the front loader is fine.

Anyone here ever have this problem or know of a solution?

 

could technically be poor contact on the cart slot related to the pins connected to the CHR chip

 

A bad PPU is unlikely, but possible. It's more likely that you have an oxidized connector, broken address line trace (the tiles are wrong, but they themselves aren't distorted are they?), or damaged 74'373.

 

Thanks for the replies. Yes, some of the tiles are distorted, but mostly just incorrect and I don't see any broken traces or damage to the board. Its actually pretty clean looking, including the connector. Everything appears to be in good shape.....except I did notice that it is missing a screw that holds it to the shell. One on the left. I can only assume that it was taken apart previously, maybe by someone else who attempted to fix it.

****edit***
I plugged the NES in again, after looking at the tiles, I suppose that some of them could be considered distorted. Most of the the tiles are just incorrect but some of them blink and are a bit wavy. Is that the distortion you were referring to?

 

Alright so it's definitely an address line issue. Are many of the wrong tiles duplicated all over the screen? Are sprites the same tiles as the background or not? Since you say that the traces look good (you should check them electrically with a multimeter's continuity test mode), I would look at the 74'373 as the culprit. It should be replaced with a 74HC(T)373 if there's a 74LS373 in there.

 

Ok when I plug in Super Mario, I can see most of the Mario sprite but not all of it. Many of the tiles are duplicated all over the screen as well.

 

I have two regular NES that produce the same kind of mangled tiles problem. Im sure the connectors are clean, i tested them on another console, no problem. Ill be following this thread.

 

Followed the traces 74ls373 and tested for continuity and as far as I can tell everything looks good. Triple checked for bad traces and everything still looks so I ordered a 74HC373 and will replace as soon can I get it.