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MD VA6 Mega Drive Model 1 Video Problem

ranfoxconn

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So I got a Japanese Mega Drive with a VA6 motherboard the other day and I tested it using two games, Bare Knuckle 2 and Gunstar Heroes and it ran them just fine. So I put in a language switch then gave it new caps and new voltage regulators. Turned the console on and it worked. Just for fun I decided to run the Titan Overdrive demo. However upon reaching the 'Titan 512C Forever' screen the system crashed. I have some pictures to show what I'm talking about. During the demo there's also some video artifacts that pop in and out. I tried putting in some of the old caps around the video circuit and putting in voltage regulators from a Model 1 Genesis that also happened to be a VA6 and that didn't help anything. I'm starting to think this may be an issue with one of the video ICs or some RAM. If so then I can at least replace it with some spares I have, save for the proprietary SEGA ICs. As far as Bare Knuckle II and Gunstar Heroes are concerned they work just fine.

Basically I want an idea of what could be going wrong with my Mega Drive.

This is my fully working Genesis VA6
MD Titan 2.jpg
This is the faulty Mega Drive VA6.
MD Titan 1.jpg
 

ranfoxconn

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I found a Genesis Test ROM and ran some of the RAM tests and the Mega Drive passed those just fine.
Compared results with my fully working Genesis and the results were identical.
 

Druid II

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It's not a problem. The titan overdrive demos go beyond the capabilities of the console, they abuse things like test pins and hardware bugs, and those do not function equally on all hardware models.

The 512 colour demo, I think, uses the CRAM swap trick, and that one requires stupidly tight timing in the code to not produce an out of sync image. Since some consoles have a bit different timings, they won't work. The difference is so little that it doesn't affect games, which gives you an idea of how much it taxes the console.

The coder of Sonic 3d and Sonic R has some explanations for the technique on youtube.
 

ranfoxconn

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So it's safe to assume the timings on my particular Mega Drive aren't ideal to run the demo but playing games I shouldn't have any issues?
 
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