SNES Hardware - OAM Failure, Sprite Problems, and Burn In Test Cart

This is my first post and I apologize if I didn't make it into the correct category, but I believe this is the best place post. I recently started a new hobby two months ago to repair and maintain broken or malfunctioning video game consoles. Specifically I have gathered four malfunctioning SNES consoles in hopes of returning them to their original state.

As an aside, I have checked the composite video cable and multi-out ports and those are good. I have also checked the power supply, power supply connector, DC Jack input, fuse, and voltage regulator. I have cleaned the mother boards and cleaned the cartridge connectors. Pretty much ruled out the common and easy issues. I have not recapped the system.

The problem I am experiencing are the sprites are on the screen, they are incomplete or composed of parts from other sprites. For example, you have Mario in Super Mario World, instead of having a yellow cape, Mario has a Mario head for the yellow cap. A second example is when you have a red Koopa shell on the ground, the shell appears to be a fish from the water level, even though it is a red shell. In my opinion, it appears that sprites are loading from images from the wrong addresses. All the sprites are incorrect for the most part.

I have concluded that the two of the consoles with this issue have either a faulty PPU chip or a faulty VRAM chip, or could maybe have a PCB trace problem. A quick glance on the motherboard appears to have a clean traces and I'm getting continuity between the the PPU and the VRAM. I am going to try re-flowing the solder of both the PPU and VRAM but I doubt this will help.

I also obtained a Reprogrammed SNES burn in test cartridge that performs a hardware test on the system. Both consoles run the cartridge but one system fails the OAM test (object attribute memory). I know OAM is related to PPU memory from google searches, but that is all I know.

1. Does anyone have experience working with the burn in test cart?
2. Does anyone know more details about OAM?
3. Is OAM failure an internal problem inside the PPU chip?
4. Is OAM part of the PPU1 chip or the PPU2 chip?
5. Is OAM failure a continuity problem between the PPU and VRAM?
6. Which PPU pins output OAM data?
7. Is the PPU chip unusable at this point because of this OAM failure?
8. Has anyone experienced OAM failure, sprite issues, or similar problems with their SNES or PPU chip?

I've looked online for OAM and all I can find are internal addresses for the OAM table for programming but I don't see any information about hardware, pin contacts, or the whether it is the PPU1 or PPU2 chip. Any help or suggestions you have would be appreciated.

I do have a BS and MS in Electrical Engineering so I'm capable of troubleshooting. I'm in the process of building up my tools and work area in my home. I'm still looking for an affordable oscope but I should have enough tools to get the problem fixed if it is reparable.

 

Your post was held in the moderation queue for some reason. Right forum, yes!

If you know the address, that should tell you the chip. This says it is internal (hmm, I always thought it was external... but then I'm not a SNES coder. Interesting).

Regardless, a lot of these problems are caused by PPU failure and yes, it's toast. You could try replacing the RAM, though.

You should be able to get a CRT scope for peanuts, if not free. The Rigol DS1054Z is a nice entry level scope, if you want to go new.

 

One of the members here linked this website in another thread. I found it very useful
http://projectvb.com/nss/logs.htm

 

Thank you for the information Retro. I will try to see if I can acquire more RAM or worse case, consolidate two broken systems into one functioning unit, which I prefer not to do. It's pretty sad PPU failure is so common.

Pikmin- Thank you, that page has very useful information.

 

Great topic, I have similar a problem, I recently bought 2 Super Famicoms, two in case one is broken ... and ofc both are broken, ebay sellers these days...

Now what I would love to know is what test on the SNES Aging/Burn-in cartridge tests what part of the system? Both SFCs fail at different tests.

(in the second picture the first 3 tests pass too, then half of the screen goes black)

Now I tried swapping the CPUs between the two systems but sadly I managed to rip 4 traces off the pcb in the first so I desoldered all its chips and parts and binned it. Now with those parts I want to revive the second.
Luckily between the two units I have exactly enough non yellowed case parts to build one good looking system.

I recon that in the first picture the ppus are broken and in the second it's the cpu that's gone overboard. So I will take the working CPU out of the first and install it into the second.

Aligning the CPU properly seems to be a complete nightmare though. Also I need to buy some flux, do you think this will do the job? https://www.amazon.co.uk/gp/product...act_title_1?ie=UTF8&psc=1&smid=A3P5ROKL5A1OLE

Does anyone know if the CPUs in the PAL systems are the same? Maybe it would be best to buy a cheap working PAL console and get a known working CPU from there.

 

Yeah what's the deal with the ebay sellers, seems like all the systems they sell have faulty PPUs.

Those are interesting results, although I can't really see what failed from the angle of the photo. I haven't seen anything online that states what each test corresponds to and if it is linked with hardware or software issues. It would be nice to have or create a troubleshooting list based off of test results.

At least you found a fix in combining two broken systems into one. For those broken traces, you can run 30 AWG wire (or equivalent millimeter size wire) from the contacts on the chip to either the vias or other locations on the board, as a fix.

I would suggest to buy a thin tip for your soldering iron in order to work with the surface mount components. I have heard that flux pens are easier to work with than the flux bottles because you can control how much flux is released and is easier to apply. Something like this http://www.amazon.com/Chemtronics-C...s=flux pens&qid=1465412588&ref_=sr_1_4&sr=8-4
Working with SMD is a pain, definitely takes skill.

For the CPU, I thought they were the same, unless it's the 1chip. My understanding was NTSC and PAL units had different power requirements but the major components were the same.

 

CPU for 3 chip SNES can be either the original S-CPU or the 2nd revision S-CPU B.
They should be interchangeable but I only read that, never verified it.

From the mere statistics on the repair log site, I'd always assume a broken CPU on a glitchy SNES.
Sometimes, rarely, it is a PPU.

 

I only sometimes take notes when I repair SNES consoles, so you should take this with a grain of salt, but in the limited notes I do have I wrote at some point that replacing PPU1 fixed some consoles I had with OAM ---> FAIL.
Unless there are some broken traces on the board causing the issue, then yes, it does mean PPU1 is basically useless at this point and can only be replaced.

It looks like the second photo might be "DMA ---> ERROR" . If that's the case it could be anything really. A bad CPU could definitely be the cause, but a bad PPU can also cause this error. Or if you're really unlucky it could be more than one thing that's failed!
But basically if games run fine but the only issue is that the graphics are screwy in some way, then it's usually a PPU issue. If games don't run, crash, or behave strangely, then it's probably a CPU issue.
As for aligning the CPU properly, it helps to do all four corners first. As long as you get the corners right, then it's easy to solder the rest of the legs. If there are some bent legs I like to use a sewing needle to nudge them back into place.

Yeah, all 3 are completely interchangeable. You can even put CPU-B into the early SHVC consoles even though I'm pretty sure all of them had S-CPU or CPU-A originally.