SNES Repair - Sprites Missing, any ideas?

Discussion in 'Repair, Restoration, Conservation and Preservation' started by amace, Jan 27, 2017.

  1. amace

    amace Active Member

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    Before I go into detail, the cartridge is not dirty, it happens with them all, the cart slot is fine. Seems that's the only suggestion I find when I've been researching this issue.

    Now, moving on.

    i recently picked up a lot of 6 SNES from eBay for $20 to try and repair. Some are in REALLY rough shape, but one of them mostly works, however the sprite layer is not working properly. This was noticed when I tried loading Super Mario World. The background and sound works perfectly, but the sprites flash, or only halfway appear, sometimes nothing at all. I'll try and take a picture later.

    I tried Toy Story, and got all the background images, but as soon as a sprite layer is supposed to appear (menus, icons, etc), they don't work or are scrambled.

    The Board revision is SNS-CPU-GPM-01

    I'm using an OEM AC adapter which is known-good, AV cable is good, all games are good. I checked the Voltage regulator, and my multimeter has it fluctuating between 5v and 6v. Is this normal? There could be a bit of error on my multimeter, or possibly the 7805 is going bad. Fuse is good, power jack is good.

    There's no signs of liquid damage on the board, but I'm going to go through checking traces soon. I'm hoping to limit the scope of my search, rather than searching all the traces, does anybody have a suggestion as to what could control this?

    My guess is the vram? Possibly the wRAM? I'm not sure it's the PPU, you would think that other issues would appear.

    Has anybody here had experience fixing missing sprites on a SNES? What is typically the culprit?

    Also, I've started recording some of the repairs and starting a youtube channel. I don't mean to seem like spam, but if you're bored, check it out. I've only got a couple videos up, one is repairing traces on a game cart, one is a full disassembly and clean of a system.

    I don't have this particular system up yet on youtube.

    Thanks for any help you can provide.

    I quickly uploaded a video of what I'm getting. Hopefully this helps with showing the actual problem.

    Also worth noting, it happens on a CRT as well as my Plasma. the TV is not the issue either.


    With Further research, I found this: https://emu-docs.org/Super NES/General/snesdoc.html#Terminology

    It's not perfect for what I need, but it does seem to indicate that the sprites are stored in the VRAM. I'm going to check the power in to each VRam chip, as well as the traces between the VRAM and the PPU to start. won't be able to do this for a couple days, but again, if anybody has any other insight, I'd be glad to hear it.
     
    Last edited by a moderator: Jan 27, 2017
  2. Pikkon

    Pikkon "Moving in Stereo"

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  3. amace

    amace Active Member

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    Thanks, I'll check it out. I love the early 90s design :)
     
  4. malcolm

    malcolm Rising Member

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    excellent video :)

    Have seen quite a few failures of super nintendos with CPU-A, they are typically the early model systems with the separate sound boards. If you have access to a flash cartridge you can try running burn in test on them, and the burn in test will often operate even if games dont normally load. Also it is normal for HV timer to fail when a system is running at 60hz, but if all else passes it could be broken trace/s somewhere on the motherboard.

    Google the results, or look at the link provided above and it should give you an idea what is wrong.
     
  5. Tokimemofan

    Tokimemofan Dauntless Member

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    I've seen a lot of systems with vram issues either cold joints or bad chips. CPU failures usually cause games to crash or be unplayable if any picture shows at all.
     
  6. Oakleaf

    Oakleaf Spirited Member

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    I have a snes and a pc engine duo with video ram problems. I think they use the same kind of ram. Same pack and pinout. Does anybody know of a modern replacement?
     
  7. Bad_Ad84

    Bad_Ad84 The Tick

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    Whats the part number
     
  8. Oakleaf

    Oakleaf Spirited Member

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    • HSRM20256LM for the duo
    • Cxk58257 for the snes i think
     
  9. Ergot_Cholera

    Ergot_Cholera Flaccid Member

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    The Duo is SRM20256LM
     
  10. Bad_Ad84

    Bad_Ad84 The Tick

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  11. Oakleaf

    Oakleaf Spirited Member

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    Thanks!
     

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