So I bought a system on ebay knowing it was broke. I asked seller for details on symptoms and got no response. After a few days I pulled the trigger and spent the $12. So far all I get is a green screen. I found a bad cap so i changed it and found that the cpu was getting hot to the touch after about 30 seconds. Not warm but so hot i couldnt touch it. I swapped it out for a known good cpu and still the problem persists. Ive replaced the 72 pin and cleaned the whole board. I cant find any obvious problems and cant feel any other chips getting hot. Throughout about 100 resets i got 1 grayish blue screen and 3 graphically buggy screens(only got a picture of 2). Any ideas of where to go next?
Looks like the PPU is at least somewhat operational, if those single tiles don't change with time. I'd check the CPU's RAM.
That was the direction I was leaning towards but I dont have much experience with these systems to properly diagnose these more in depth problems. I have a spare board that had a bad ppu so I'll steal the ram off of it and see what that does.
Swapped out the ram and still nothing. I found what looked like a bad trace on the psu and bridged it and still the green screen
It'd be weird to me if enough of the PPU is working to draw a stable green screen with sprites that look like they're valid CHR contents, but not enough to operate.
Do you have any test equipment? (scope? logic analyzer? voltmeter? frequency meter? flashcart? a resistor and pair of headphones? random components?)
Only thing I have is a generic multimeter. I noticed somebody else has disabled the lockout chip presumably an attempt to fix the problem. The board is a cpu-10 if that helps.
At this point, the last thing I could do with just a multimeter is make sure most of the lines in/out of the CPU and PPU are still toggling. (logic tester, if you 'meter has it. Vac otherwise)
nesdevwiki:PPU pinout,
nesdevwiki:CPU pinout.