Very strange Sega CD video issue

[+-^CrossBow^-]

Still working on this and trying to figure it out. Definitely seems to be related to my 32x somehow. I made a quick YT video of it last night. First part shows the Sega CD bios screen looking fairly normal with the 32x attached and powere up. You can being to make out some sparkles in the video beginning to occur. I then come back after about 30 or 40min of it being on and turn the system back on with the 32x attached so you can see the snow pattern that is happening. I then without turning off the video, remove the 32x from the top of my genesis and power it back on, and you can see that the video is normal again.

 

I do have the metal RF blocker shields installed in the cartridge port, but this issue will occur regardless of them being installed or not.

 

The video source in this YT vid is with my AV cable directly from the genesis AV out and not from the 32x. So the issue is being generated from the Genesis side it would appear. It will still do and look the same if I'm taking the video from the 32x.

 

the genesis is running an ambient air temp of about 112°F as measured from my temp probe and Fluke meter around the AV port inside the genesis. This seems excessively hot to me.

 

With the 32x removed the video issue doesn't appear at all and the Genesis seems to not get nearly as warm when playing.

 

Graphics issue only occurs within the frame of the Sega CD bouncing logo as you can see in the video. When this is happening and I play Sonic CD the issue only appears within the windowed frame during the cartoon intro but not outside the frame and not within the game itself. Even the bonus stages that use the rotation and scaling look normal. So it appears to only affect FMV or some video input coming from the Sega CD and with the 32x attached and the system fully warmed up.

 

Does this explain better what I'm seeing and does anyone have any ideas on this? I'm trying to source or borrow another 32x base unit to see if it is the 32x itself or something within the Genesis.

 

[SignGuy81]

I would take the case of the 32x apart, then put it in the genesis without the case and check individual chips with the temp probe you have and see if anything in the 32x is getting extremely hot.

[Osgeld]

to be fair 45 (ish) C is not THAT hot for electronics the Tj for a 7805 is 150c max

 

there's a ~3c difference tween Tj (junction temp) and the thermal pad on the standard TO-220 pacakage

 

SOOOOOOO lets say your reading 44.blah with the case open and attached to the heat sink, the Tj is like 48ish

 

to put this in perspective for people who think in F, a standard issue generic 7805 should not be getting slightly wacky until damn near 300F case temp

 

do you suspect its getting 3x hotter with the case on, cause that should be pretty obvious as the plastic should be getting a waxy finish around the offending area, I am starting to lean to a cap issue or maybe when you recapped the 32X there's some side effect from using ever so slightly different caps or some residue from the old ones causing increasing capacitance tween traces or some other magic bullcrap voodo

 

hell some fluxes will cause increasing capacitance / resistance issues over time and heat as they are mostly organic compounds

Edited July 11, 2017 by Osgeld

[+-^CrossBow^-]

Well to give an update again...here is what I've done to confirm some testing...

 

The main Genesis with a 32x attached and plugged into the model 1 Sega CD takes about 3 hours to start doing this with no cart inserted and just running the sega cd bios screen into.

Same Genesis with a cart plugged into it will start doing this after about an hour and a half or at least, that is when I noticed it was doing it.

 

Another Genesis I have doesn't do this at all even after it was running a game plugged into the 32x in demo mode for over 4 hours. The entire system was also much less hot as opposed to the other one.

 

The video issue doesn't occur at all if you remove the 32x.

 

The game I was running was Wiz N Liz which, isn't even a 32x game. The AV is coming off the Genesis itself and the 32x is only attached as it appears to be the cause for some reason.

 

When it happens, again, only the FMV stuff on SegaCD games is affected. Cartoon Intro of Sonic shows the snow pattern, but only within the small window frame that the intro is being shown in.

 

Everything is plugged in while this happens. So even though in the video above I used the Genesis AV port for video and not the AV out from the 32x, I still had power applied to it. Same video issue occurs from the AV out on the 32x as well, but only from the one Genesis.

 

Now, the two Genesis systems aren't the exact same. The problem child is a VA2 with the following Mods applied:

S-video added

Region switch added

YM3438 piggybacked onto the original YM2612

RCA jacks installed for Composite and audio

 

The other model that doesn't cause this behavior is a VA6 and only has the following mods applied to it:

Audio L/R RCA out

YM3438 Piggybacked off the YM2612.

 

That's is..no other mods.

 

Last night I placed my Fluke temp probe and taped it down as best I could to the center of the 68k. After an hour and half with the snow video pattern taking place, the temp was 151°F. Tonight I will do the same test on the other model to see if the CPU temps are roughly the same. The heat is concentrated along the side where the VRs are located of course and towards the back half of the console. Hence why I probed the CPU since the system doesn't reset or shutdown at any time during this.

[+-^CrossBow^-]

Didn't do the temp readings last night...but I was able to simulate something interesting..

 

I took the 32x off and put in my cart of VR Racing. I left it running for about 3 hours...Turned off the Genesis, pulled out the VR Racing cart and turned it on. The Sega Bios was normal. I then plugged the 32x into and turned it on and the video was immediately showing the show pattern. So this means it isn't a heat issue from the 32x and is all from the Genesis itself. I also noticed at this time something else I hadn't tried before. I unplugged the 32x without turning off the genesis and as soon as I pulled the 32x power cord out, the snow pattern went away. Since I'm using one of Golden.Ax converted GC power supplies, I then plugged in an actual model 2 power supply to the 32x and still had the snow pattern. So I can at least rule out that the supplies are the issue. But what is certain is that when the Genesis gets to a certain internal temp or a component gets to a certain temp, combined with the 32x and that 32x being plugged in with power, and all of that plugged into a segaCD model 1, I get the snow pattern.

 

I know it seems I'm going in circles, but I'd like to think I'm slowly getting to the point of isolating where the cause might be. I've been suggested elsewhere to use a can of air turned upside down to insta cool components one by one on the genesis to see when I can make the issue go away. The problem with this, is that means running the system without the cover and doing that this issue never occurs because there isn't enough heat built up to cause this to happen.

[+-^CrossBow^-]

In an attempt to lower the temps on voltage regulation, I've just replaced the original 7805Cs with a pair of L78S05CV. Basically a 2A output +5 linear regulator. Hoping the 2amp versions will run cooler since they won't have to put out half of what they are rated to handle. Doing a burn in test now with the sega CD bios up and running with the 32x attached. We shall see...

[Osgeld]

well it will help a little, a typical 7805 has a 65 degrees per watt (+ a few tween junction and case) vs those say 50 c/w

 

so the eyeball estimate formula is

 

(Vin - Vout) * I = W

 

W * c/w = temp (without heatsink)

 

ie (9-5) * 0.5 = 2, 2*65 = 130c (without heatsink)

[+-^CrossBow^-]

Well..the system has bee up nonstop for over 3 hours now. The SegaCD bios screen still looks normal. So I'm now inclined to believe that the VRs were part of the issue. The system isn't nearly as warm as it usually is either after this amount of time. So yeah...I will keep it up and running an likely play some more Star Cruiser on it to really get the system going and make sure.