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Konami GX System issue (Gokujou Parodius)

pvwradtke

pvwradtke

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Hi folks, I have a Konamy GX System board with a Gokujou Parodius game sub board. It's my only GX system board and game, so I can't really swap parts to better troubleshoot the issue. With the board, the game boots to garbage screen - the game seems to be running, because I can go to the test menu, start a game and I can hear corrupted sounds. Video and pictures below.


Then, if I remove the game sub board, the motherboard seems to boot quite fine. It displays a message to power off and connect the game board.


Has anyone seem this issue before? If yes, what's your best guess? Is it a corrupted ROM, or is it most likely a custom IC that's busted and the game board is dead? I'm considering picking up an EPROM writer if the ROMs could be the issue, but if that's nowhere close to where the problem is, then I'd avoid it for now. Comments and ideas are welcome.
 

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What is the voltage on the power supply?
And have you taken out the eprom, and check for any corrosion on the legs?
Also have a look at the board, see if there are any broken traces.
 
kingau said:
What is the voltage on the power supply?
And have you taken out the eprom, and check for any corrosion on the legs?
Also have a look at the board, see if there are any broken traces.
Click to expand...
Voltage is 5.02V (though I'm far from ideal, as I have an ATX PSU connected to my board). I have taken out the EPROMS and I have reseated them, and I spotted no visible corrosion - though I'd ave to check under a microscope to see better. I did a visual inspection and couldn't see bad traces, but I still have to do a deep continuity check using a multimeter. From your comments, I take it's unlikely that the ROMs themselves would be corrupted, but rather something with the board or voltage could be the issue, correct?
 
Your voltage is spot on. Without another motherboard or game it's hard to know what is the issue. Could be a bad custom, cold solder joints, bad RAM, bad buffers,...
Get a logic probe.
 
ic3b4ll said:
Your voltage is spot on. Without another motherboard or game it's hard to know what is the issue. Could be a bad custom, cold solder joints, bad RAM, bad buffers,...
Get a logic probe.
Click to expand...
Thanks, I'll pickup a logic probe - though I'd love to get an osciloscope sometime as well :). I have a friend that has a System GX board and we talked about doing some tests next time I go there, but COVID-19 is keeping us from doing that. Thanks for the suggestions, I'll keep looking on it and report back at a later date.
 
I'll help you if I can, don't worry about that. The first thing is to try and isolate where the problem lies, either the ROM board or the motherboard itself. From there we can start the diagnostics. But get that logic probe!
 
Uninitialised EEPROM error upon boot most likely. I'm not going to sugar coat it... This is either a bad MaskROM (possible) or an issue with the motherboard (likely). Konami customs die a lot on these boards, from my experience. You can replace the motherboard fairly easily. There are cheaper games that use it and it's probably easier and cheaper than tracking down the fault. With that said, test the full stack with your friend's.
 
ic3b4ll said:
Uninitialised EEPROM error upon boot most likely. I'm not going to sugar coat it... This is either a bad MaskROM (possible) or an issue with the motherboard (likely). Konami customs die a lot on these boards, from my experience. You can replace the motherboard fairly easily. There are cheaper games that use it and it's probably easier and cheaper than tracking down the fault. With that said, test the full stack with your friend's.
Click to expand...
Thanks for the tips, will wait for COVID-19 to be able to visit my friend and do a full test.
 
Hi folks, just to follow up, and to let @ic3b4ll know he was right on target. I was able to isolate the issue testing on a friend's stack. While my main board boots without the ROM board, the ROM board is actually fine and the main board is busted. My ROM board works just fine on my friend's System GX, but his ROM board doesn't work on my System GX (exactly the same issue). So yeah, faulty System GX motherboard.

Took me almost one year to get this properly tested (thanks, COVID-19), but now I can move forward and solve the issue.
 
... and this kids is why I keep 3 different types of 4 slot Neo Geo stacks around.
 
Good for you @pvwradtke, I got a Sexy Parodius a couple of months ago and love it. A friend of mine did tell me these boards are finicky. Just like @ic3b4ll mentioned it is wise to have multiple main boards to keep for backups.
 
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