SNES (Orig) Repair/Diag Help

SNES (Orig) Repair/Diag Help
by on (#212632)
UPDATE: I got it fixed, I touched up the solder job on the two SRAM chips and the bus pins on the PPU1 chip and it started working right. I guess I'm not using quite enough heat when re-soldering the chips on the board, touching them up a 2nd time a little slower seems to make it look better and clearly I had atleast 2 bad solder joins/bridges, but I'm still learning =). Now onto the next system which I'm guessing PPU2 since it has sprite data missing and it seems like different modes/screens makes it crash.

Working with the older style SNES boards and trying to learn some new things by repairing old consoles. Anyway the board I'm a little confused on is a SHVC-CPU-01 (with the dedicated audio processor board).

EDIT: I found a tiny solder bridge I overlooked on pins 9 & 10 of the cpu, so below isn't really related now. Currently getting vertical lines in the foreground (covers sprites and background). Super Mario World plays fine, no crashes, just the graphical issue now. I'm thinking PPU1 or one of the SRAM chips I installed was bad.

Here's a photo of it's current state. (The big bars cover everything and are solid, behind it it seems to function somewhat normal. Sprites seem to look correct so I think that rules out PPU2.


Skip below if you don't want to see what cpu pins 9+10 bridge does.

When I first got it, it ran fine but had jumbled up graphics, based on DogP's repair logs ( it looked like PPU1 failed except I got static like lines as well. Long story short I swapped PPU1, PPU2 both with no change, then after replacing U4 SRAM chip the static lines went away. I figured it was a bad cpu by this point, but don't know any bad boards with a known good cpu so I swapped the cpu from a board that booted to just a black screen to see the effect. I figured if I got a black screen, good sign that cpu was junk and could try another (have 3 other systems with black screen issue, not cart connector etc). Anyway, after swapping out the cpu now I get nothing at all.

I checked the reset pin on the cpu, and it's under 4.3v (0.7v if I remember right) so I figured I'd follow the reset signal from the CIC chip on wards. At the CIC chip pin 10, reset is 4.96v, same as the other black screen consoles which tells me the CIC is communicating with the game fine. Checked pin 34 on PPU2 which is reset in from cic and same voltage. Output from PPU2 (pin 33) to PPU1 reset signal is nothing. Does this suggest the PPU2 chip I transferred is dead? I didn't do any of these tests before swapping chips and I'm a little bit new on soldering the larger SMD chips, but I don't see any solder bridges. Chips were removed with a hot air rework station.

I'm fairly limited on diag equipment which is why I jumped to the guess and check method first. Also should mention, the board I pulled the chips from had pop or something spilled in it and had a fair bit of corrosion so figured it would be the best board to use for parts.

Any advice what to check, or should I just swap the orig PPU2 chip back on the board since it seems like swapping the chip had no effect? Also I reflowed the CPU legs before swapping, and it made the system boot to the nintendo screen with jumbled graphics and then crash, so pretty sure the first cpu is bad, and the U2 SRAM was bad.

I have the pinouts for each of the major chips which is what I've been using to see if a given chip is active or not.

Any help would be great, let me know if I missed any details.