View Full Version : A few questions about the video hardware
Hi! I'm obviously new here and since I though that this is the best spot to do so, I'd like to ask some questions regarding the video hardware. It's all about the PAL Mega Drive, just to make that clear right away.
First of all, I'm having some problems with the connection to my HDTV via RGB lately. The whole image rolls down the screen and when it reaches the bottom, it comes back out on the top in an endless cycle. It somehow depends on what is shown in the game since this doesn't always happen and some games or at least parts of them work just fine.
I haven't had that early with my setup. It worked perfectly everywhere but one day when I hooked it up again to test a new game these problems started. I have tried varios of my systems and they all were the same. It still works fine with an composite scart cable and the RGB cable worked just fine on my late 80ies CRT.
I think that it's the cable and that there is something wrong on the sync lines but with the randomness and given that it works on the CRT I'm really not sure anymore.
Now a more general question about my hookup.
I always get vertical lines in the picture. They are especially noticeable on blue backgrounds where every second line is a little bit darker. I could even see them on the CRT TV. It's more noticable on my Model Is then it is on my Multi Mega but the latter one on the other side has some noise in the image, again especially noticable on the blue line (I can shut off colors on my HDTV).
Are these lines normal and if or if not, is there a fix for that?
At last a general question, wich has always interrested me, but I could never find some answers about that. The Mega Drive / Genesis always has that line of flickering colored dots at the bottom of the picture and I always wondern why that happens and what that is, since it is never mentioned as a fault in the VDP or mentioned at all. What's behind this flickering?
Okay, I think that's more than enough for my first post. I hope everything is understandable and I hope, that my questions can be answered.
Isn't there anyone who can say something about this? All I want to know if my RGB cable is broken or if there are other errors and where those other issues come from. (just throw in some tech specs)
What I forgot to mention is that the image sometimes may quickly jumps down a few lines and up again every half second or so. This also depends on what Image is shown.
I think I found a good example of how the vertical colored lines look: Hanover Bars (http://en.wikipedia.org/wiki/File:Hanoverbars_without_PAL_delay.png)
The difference is that my lines are vertical and not horizontal and they aren't that strong, but they definately look similar. I don't think that this error has much to do with the one I get from the Mega Drives, even though it's kinda funny how it's called when you consider where I live. :mrgreen:
09-08-2010, 07:57 AM
I think a picture of what's going one would be a lot more helpful then an explanation.
You say the composite is just fine, and that the SCART RGB works ok on your CRT, but their is a problem with your HDTV. There could be a number of reasons for that, but seeing exactly what's going on would be a big help in limiting it down.
Vertical lines suggest your TV is not (fully) going into RGB mode, as these lines are stuff that only composhit has. Crappy cables have tendency to put the TV into an intermediate state like that... and seems the HDTV you got is not particularly fond of it....
...at least this is what I think of it
Okay, here are examples of the two games that came in with the mail today.
Here is a video of Galaxy Force II (http://www.youtube.com/watch?v=0g6hHHJg24A). The quality is very poor since I only have my cellphone cam but it shows both errors. The image rolls on the title screen and in gameplay and does those little jumps in the scene select screen. It's a bit harder to see this one with the crappy quality but at least you get the idea how it turns out.
Here is a screenshot of Mega Swiv (http://spindash.de/forum/master_dl/lines.jpg), wich runs just fine. I made this one to show the vertical lines.
As for the flickering stuff at the bottom that always occurs, just look at some random videos on YouTube wich were recorded off of real hardware like CGRHD's for example (http://www.youtube.com/watch?v=liBKYDq7pdc). You will get that on real hardware virtually anytime, unless that portion of the screen vanishes into the overscan.
For further info, I own this TV set (http://www.home-entertainment.toshiba.co.uk/Regza-LCD-TV/50-LCD-TV-screen-size/55-Regza-SV-Series/) (actually the german 685D version but it's the same)
09-08-2010, 11:15 AM
I get these lines too with my PAL Megadrive on my several years old Samsung LCD. I'm not sure of the cause, but I don't recall it being visible on my old CRT. FWIW it doesn't matter whether the video is coming directly from the MD or through the 32x.
Okay. Here's another round of testing infos and stuff.
I measured my RGB cable following this schematic (http://www.wda-fr.org/forum/images/uploads/Casio/mega2_130.png) and it seems to be fine. The color lines with 75 ohm resistors measure a little less and have 70 ohms (because of the capacitors?) but there is one real difference. According to the schematic the ground has to be connected to pin 9 and 18 but that isn't the case on my cable. Pin 9 and 18 are completely missing. Does that make a difference?
I made some tests with the cable and my Master System. All games run fine. Same thing goes for the Power Base Converter. SNES and all other systems work fine (with their respective cables of course).
More testing with the cable, this time through AV2 wich is composite only. Here Galaxy Force does those little jumps all the time and the dark backgrounds flash white at the beginning of each jump.
Then I took my composite only scart cable and there were no jumps or errors at all, different from what the composite signal in the RGB cable gave me.
I'm really confused now. Some things on the RGB cable work, while other don't. Composite is also flawed, while it works fine with a composite only cable.
This again makes me think that there is something from with the RGB cable, since not even composite works properly on that one.
Oh, one more thing. I believe that my TV takes all these signals as progressiv. I only get infos about the sorce on HDMI but when I use the still image function I get an absolutely perfect image. When I do this on interlaced material it will only store one of the two fields wich is easily noticable. Just wanted to toss that in, since it might help.
As for the lines. I recall seeing them on my 2004 29" CRT wich I don't have anymore, so it's not only the HDTV. Other systems besides the Master System don't show these lines. I remember that there was some kind of mod for the Neo Geo wich removes vertical lines on RGB images. Don't know if these lines are similar to the ones on the MD though.
All this stuff really makes me dizzy and I won't get a good sleep until I know what is wrong.
I'm really sorry to bump this with a doublepost again but I dug even deeper into everything and I finaly found out some things that are usefull.
Those vertical lines really do come from the composite line. It has something to do with the Model 1 giving the sync signal over composite and that produces those lines. Model 2's don't show those lines since the sync works different there. There are actually fixes around here for model 1's but they require mods on the system itself. Let's put this topic aside now.
The colored dottet line at the bottom seems to have something to do with the VDP writing to memory in certain ways. We can put this aside now aswell.
Now to my personal problem again. Forgett about the missing pins. I installed them and nothing changed. On the other side, I noticed that my cable doesn't have the capacitors that are in the diagram, but it doesn't seem to make a real difference.
I wiggled the connector around and in and out and this got some interesting results. Depending on how deep and in what angle I insert it the picture varies. Sometimes I get composite that jumps like before and sometimes I get composite that works. While it worked I sometimes had to switch between PAL and SECAM to get it with color.
If I do it in a different angle I get green only RGB image wich doesn't jump or roll and if I hold it JUST RIGHT I get an absolutely flawless RGB image! If I let go of the connector just slightly the image moves a tiny bit to the left, gets a very little wobbly vertically and starts jumping or rolling again. For this result I insert the connector about halfway and tilt it so that the right side (the one with 2 pins on the top row) is inserted slightly less than the left side.
So what does all that mean? Is the TV confused about taking composite as PAL or SECAM? Wich of the pins is the one that I lift up high enough to get the picture right, since this would mean, that the picture will always be right, if I remove it.
Or is it just plain by accident and I can't make a permanent fix?
Allright now I have one final question about the hardware itself, if you're still reading all my garbage.
Since some games run just fine and others don't, I was wondering if the VDP has different modes. I know that it switches into a different mode for Master System games but does it have different modes/resolutions (apart from NTSC/PAL) for MD/Genesis games aswell?
EDIT: Moar stuff! I tried out my japanese MD and my Nomad and both of them work perfectly with the cable. My region modded european MD however doesn't. I still get the same rolling/juming issue when it's switched to NTSC 60 Hz. I don't get it. This is really starting to loose any kind of logic or sense.
09-09-2010, 12:59 PM
Why use the composite cable to sync with? The composite cable has a lot of shit going though it, it is a very noisy cable.
Just hook that up to the sync pin on the scart cable.
The horizontal lines could be related to the composite cable, or it could be because you didn't shield the cable and the entire thing is picking up noise. Of course this is an HDTV so every flaw will show up on the screen.
FINALLY! I found a solid solution!
Putting all logic aside I went through all the pins and bent them away to take them out one by one. PIN 5 (http://www.gamesx.com/avpinouts/genesisav.htm) was the stinker. Works with everything now. It doesn't matter if it's model 1 oder model 2 and it doesn't matter if it's 50 Hz, switched 60 Hz or pure 60 Hz from the jap MD or the Nomad. CRT is still working aswell.
It seemes odd to remove the sync but the MD/Genesis seems to sync on composite just fine and my TV must have gotten confused with the two sync lines. I don't see any downgrade in the picture so it seems that the composite sync is just fine.
Yeah, it produces vertical lines on model 1's (image is absolutely clean with model 2's) but that has more to do with the encoder in those than the general shittiness of composite (as a sync) I think.
I'll put the vertical lines aside for now. The cable is working and I had enough trouble for a while. When there's a way to get rid of them with just the right cable pinout, I'll get to it again. If it's just possible to remove the lines with internal mods (I read that this is the only way somewhere on this board), then I'll pass.
EDIT: Ah man I should've tested some other games than just GFII all the time. Phantasy Star IV has a little bit of jumping at the SEGA Logo and at the very beginning of the intro, before the text fades in. Guess I have to pop in some games and look around if I get this at certain points.
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