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Odd Sega 32x and SegaCD video issue (Maybe Heat issue?)


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#1 CrossBow

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Posted 10 July 2017 - 09:58 AM

I've posted this at AA and on the Sega-16 forums as well so if you already seen my praddle on about this I apologize and you can ignore. That said...

 

I noticed about 2 weeks ago, something odd on my Genesis/32x/SegaCD combo setup. Basically after the system has been on for about 30min to an hour, there appears to be a great deal of heat built up inside the Genesis itself. I actually measured this with my Fluke temp probe and the ambient air temp in the Genesis reaches about 112°F around the AV port. That seems excessively hot to me but perhaps not?

The specific issue this seems to cause is that video overlayed from the SegaCD itself will show up with a snowy like pattern on the screen. But only from the video from the SegaCD itself. I've posted a link below showing the effect. Basically at first when you power everything on and look at the SegaCD bios screen everything appears normal. Then after some time, it will produce a horrible graphics corruption issue as is shown second in the video. Then, if I remove the 32x completely from the system the video is normal again.

Now I have found out that the 32x appears to be the cause. Not sure why, but it is. In the video, the actual video you see on my TV is using the AV out port on the Genesis itself and not from the 32x. However the same results appear from the 32x AV port as well. So the video corruption isn't from the 32x encoder but somehow from a combination of the 32x being attached along with the SegaCD.

So far this graphics corruption isn't actually seen in games with the exception of those using FMV. As an example notice in the sega CD bios screen the graphics issue is only within the window frame of the bouncing Sega CD logo and doesn't affect the text graphics outside that? When I play Sonic CD with the system warmed up and doing this, the graphics glitches are present within the window showing the Sonic CD cartoon intro, but not outside the frame of the intro and do not appear at all within the actual game. Even on the bonus stages where the rotation and scaling effects are being used do not show this issue. Normal cart games are fine as well and if I remove the 32x, the Genesis doesn't seem to get as warm and of course the graphics issue from the Sega CD doesn't appear at all.

Has anyone seen anything like this before? I'm trying to get ahold of another 32x base unit for cheap that works to see if it is the 32x actually causing the issue or something within my genesis somehow.

https://youtu.be/LMS6E46EhUo


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#2 RickR

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Posted 13 July 2017 - 03:49 PM

I would guess an overvolt power adapter.

#3 CrossBow

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Posted 16 July 2017 - 05:47 PM

Well, I realized I hadn't updated this so wanted to point out a few more things I found out and what surprisingly seems to have corrected it, or at least worked around the issue:

 

With more and more testing, I found that what triggers this is obviously heat related and kicks in once the CPU temp hits about 150°F and the ambient temp in the Genesis case is about 112 - 114°F. However, while triggered by temps, if it also requires that the 32x be attached and...be plugged in with its power adapter. So if you unplug the 32x the snow pattern would immediately go away regardless of the high temps in the case. Plug it in and the snow pattern would immediately come back. 

 

Now to add more lemon into this mystery, the 32x doesn't even have to be warm. In fact, I did a test where I took the 32x out and had the genesis playing VR Racing in demo mode for about 1.5 - 2 hours. I was curious if I could get the Genesis hot enough on its own to produce the effect. No such luck as the SegaCD bios screen looked just fine after this. Then I plugged the 32x into the Genesis and plugged the power to the 32x and turned it on and there was the snow pattern! Remember the 32x was just plugged into the genesis so it hadn't been powered on but seconds. So the 32x is a trigger, but apparently not the cause.

 

I finally had a theory and from most of the temp measurements that the bulk of the heat in the genesis was coming off the original 7805C regulators. These are supposed to be +5 volt 1amp output regulators. But they did seem to be getting very hot. Not enough to shut them off, but so hot that the heatsink and AV out ground shield plug was too hot to touch. So...what did I do?

 

I replaced both VRs with 78S05CV versions. These are modern +5 linear VRs with a 2amp output rating. My theory is that with the mods in my genesis, the genesis itself is pulling more current than the original VRs were really ever expected to generate. Add the 32x into the mix and now there is additional current being fed into the system that is causing an over current situation. Again not enough to fry anything or cause thermal shutdown on the VRs, but enough that it had to be given off as additional heat.

 

So now with the new VRs in place the console doesn't quite as hot as before. It does get warm, but only slightly more than the other Genesis I tested with that does NOT produce these results. Either way, I was playing Star Cruiser last night and had it running from 6pm until after 1am nonstop and the Genesis no longer produces the snow pattern with the 32x in place from the SegaCD video side of things.


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#4 RickR

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Posted 16 July 2017 - 06:05 PM

Thanks for the follow up.  Very happy to know you got it solved and working properly.  :thumb: :thumb:



#5 CrossBow

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Posted 17 July 2017 - 10:54 AM

Thanks for the follow up.  Very happy to know you got it solved and working properly.  :thumb: :thumb:

Not sure I would say I got it solved exactly. It is all theory and speculation and adding in higher amp output VRs is really more of a work around than a fix. Afterall, i didn't solve the issue causing whatever it happening, just put in higher tolerant stuff to counter it. Will have to see if it resolves the issue in time.






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