The same for me, my picture is near perfect. So near that for me it don't need to be better, and i'm a perfectionnist.
Yeah, at this point I'm more interested in what exactly causes the interference, than how to fix it.
VRAM is too close to the encoder
And I was not sure about the chroma carrier but it seems like the chroma carrier clock on the MD is too strong. On other machines using the CXA1145 the image is perfect or near perfect.
On my own personal designs using the CXA1145 (SUPERGUN), I have dot crawl problem but that's caused by thermal fluctuations on the quartz oscillator crystal.
If I change the circuit for an square wave generator (just like the square wave signal the MD sends to the CXA chip) I'll get rid of the dot crawl but I'll get JAGGIES and crappy RGB output on the buffer ....
Nice, huh ? :shrug:
You need a RC filter to cut down the corners of the square wave. There actually should be one in MD, but the capacitor is on the weak side.
VRAM too close to video is one thing to consider, but then again, MDs in same board version have it and don't have it so there's more to it...
Mida sa loed ? Nagunii aru ei saa ;)
It's impossible to completely get rid of the jailbars because all Yamaha VDPs are based on the Texas Instruments TMS9918 and that chip do suffer of the jailbars effect too ... :lol:
The MSX2/2+ (V9938/V9958) is also plagged with the jailbars stuff. Even the V9990 chip (does not have anything from the TMS9918 in it) has some issues with these jailbars.
Oh well. Glad to know you guys could figure out means of making it acceptable. :thumbsup:
Checking the schematics: Pin 50 on the VDP is the same line that C28 sits on, so removing that resistor is the same thing as disconnecting pin 50 on the VDP. I think it's safer to do that then trying to pull the chips leg off...
Yeah, that's far better. I slightly warped pin 49, and I was very careful. I've been looking for a way to get rid of the jailbars for a year now, and nothing was going to stop me.
What you're saying would suggest all standard MD based devices have identical RGB artifacts under equal conditions. (proper cables, no outside interference like TV settings, etc). No matter its model and revision. Whether or not 32X, Sega CD, SMS mode, or other upgrades are involved. Given those still must use the console's VDP. I don't recall any significant VDP improvements being done in MD's life. Perhaps it may have messed with game compatibility too much?
Which leads me to another question I never even considered to ask. Do the Pico, MegaPlay, or MegaTech also experience these bars? They're just different enough it might be fun to look into.
Last edited by Lum; 11-21-2011 at 12:48 PM.
Ok with my offical rgb cable for my model one it reduces the lines aka jail bars.
I can post a nice picture of the board of my rgb cable and what chips are one there.
This awful image is output from a Yamaha YM2302C chip (V9938) composite output pin.
Board layout is pretty poor. The computer in question is an NMS-8020 that was converted (by myself) into an MSX2. I used leftover parts and the VDP was salvaged from an 80 columns expansion cartridge which was meant to be used on MSX1 computers (what a waste of a great VDP chip lol :lol:).
There's a LOT of room for improvement but I would need to use RGB instead.
Edit: If you look at the picture closely you will notice that along with the usual jailbars from the VDP DRAM refresh cycle you see fuzzy noise. That's noise coming from the Z80 bus. ^_^
(oh and also there's a bit of fuzziness from JPEG compression too) ;)
Last edited by l_oliveira; 11-22-2011 at 08:40 PM.
Without pin 50 connected no more jailbars on my plasma.
thanks for the tips guys :)
(japanese megadrive (haa-2510 ic bd m5 VA1 837-6832)
original ac adaptator 9v/1.2a +step-down converter 220/110
Last edited by sdekaar; 04-08-2012 at 12:30 PM.
can the same workaround be applied on the SMS2? I added an rgb-out on my console and I get those lines, IIRC the sms2 uses the same sony chip... has anyone looked at this by any chance?
Last edited by keropi; 05-03-2012 at 06:44 PM.
Try a crt tv and there are no jailbars on a crt tv with scart rgb.
Pin 4 of the encoder chip is the blue input ... Guess what, pins 5 and 6 are the CHROMA carrier input pins. :)
Last edited by l_oliveira; 05-12-2012 at 06:05 PM. Reason: typo
Hardware engineers missed that back in the 80s and we're only now discovering the problem... Geez.
I wish we had documents, notes, diaries of the design process of early Sega hardware. Reading that kind of stuff is very, very interesting, there are many of them from the old Commodore staff (the C128 one is insane).