Strange graphics problem

Hello everyone,

I have a very strange problem with a SNES i got from a friend for repair.

For test i popped in Jurrasic Park, all seems normal but when i start the game, the player is invisible. Same for Mortal Kombat. Looks like a missing sprite layer
I runned SNES TEST Program, but it says PASS for the whole system.
Strange that the sprites are all visible with the test cartridge.
So i changed the both VRAM to known good chips, but same problem.
Then i tested Super Mario World and... Mario is visible. BUT it seems the sprite layer behind the first background layer. So Mario disapears behind bushes walls and so on.

anyone a idea if this is a PPU problem and if yes wich one PPU1 or 2 im not sure about adressing and such things.
I dont want to change all chips for finding the problem.
I have all chips as spare and able to solder and desolder it, Oscilloscope und much more.
But i want to solve this strategicaly

Any tipps what i can check ?

here are 2 videos wich show the problem.

http://youtu.be/nSx7rNAX-wo

http://youtu.be/T66dEu9EkwM

Greets Rotary

 

Try cleaning the carts. Had a similar problem with a copy of Mario Kart where all the karts were semi invisible. Cleaning the contacts did the trick.

 

nope, alle games run fine in my own snes. the socket is clean, too. exchanged it for a known good one, just to be sure. Same probelm.

Thinking of the WRAM now. I read about most games write the background and spritelayer priority first to WRAM then to OAM RAM.
what do you guys think.

http://youtu.be/nSx7rNAX-wo

http://youtu.be/T66dEu9EkwM

 

Ist working like new now.

For those who are intereste in what the problem was....

It was a bad PPU 2. Changed it to a good one and it works again.

 

Thanks for the info.

I'd have left it - that looks pretty cool! heh

 

Where does one buy a replacement PPU? I might as well get another SNES anyway since finding trashed ones are a challenge.

 

You can buy junk labelled ones of ebay, sellers are usually located in Japan.

 

FYI, that was a layer priority error. And the signals for that seem to travel through the mother board from one PPU to the other.

Chips can rust internally and lose connectivity to the external world. It's a common problem on older hardware...