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SNESNESCUBE64

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Blog Entries posted by SNESNESCUBE64

  1. SNESNESCUBE64
    This was a fun one as it was very interesting problem. The game itself worked suprisingly. However, there were issues with the graphics. 

    To me, this looks like an addressing error, as the game is fine but the graphics aren't quite there. I figured that it was a problem in the decoding. As shown in the schematic snippet below, this 7442 helps control which ROM bank, RAM, POKEY sound chip, or the user inputs like the trackball.

    Ultimately the bad chip ended up being this 7442. It's always nice when repairs are quick. Unfortunately, I don't have a way to test everything at the momment. For example, I don't have a trackball to test input with. I also didn't bother hooking up RGB since black and white composite was there through test points. Maybe there will be a second part depending on whether or not these things work correctly. Other than that, it just needs a burn in test, then it will be good to go.

  2. SNESNESCUBE64
    On the bench today was a neo-geo sent to me by GameN' Clyde with video RAM issue as shown below.

    Symptoms - no boot, Video RAM Error
    Solution -two pins on the Neo-GC2 chip were shorted together, fixed as shown below.

    I'm really looking forward to playing some neo geo games, I can't wait to finsh building a harness for it and picking up some games.
  3. SNESNESCUBE64
    This was an old repair that I did a while back, there was a lot wrong with it, surprisingly all CPU board issues...
    Symptoms: -5V rail was shorting to ground
    Solution: The bypass cap connected to the -5V rail had shorted, needed to be replaced. One thing to note is that several capacitors on this bubble bobble boardset had started leaking, so I ended up replacing all the capacitors with new ones.
    Symptoms: Not booting
    Solution: The game was stuck in a reset loop, it ended up being a bad 6264 RAM chip (the work ram). Game fired up after replacing it.
    Symptoms: Garbled up graphics and Common RAM error

    Solution: The garbled up was an easy one, there were two corrupted EPROMs, reprogrammed accordingly. The common RAM error had me stuck for a while. To make the story short, it ended up being the PAL at IC49 ended up being the cause. Replacing that solved the issue and brought the game to full working order.
  4. SNESNESCUBE64
    Symptoms - VERY QUIET audio, was barely audible with my audio amp all the way up
    Solution - There was a single burnt resistor, R13, which was just a 1k ohm resistor. After replacing that and the damaged capacitor that was next to it. The resistor is connected to the 5V rail, so based on the fact that it burned up makes me question whether or not the power rails were swapped around on accident. I got half a hacked harness in the box, so that further supports this theory. 

    Anyway, this one is good to go, remember to hook your harness up right!
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