Sync problems with NTSC Sega Genesis

[marqs]

@dead_screem Yes, there seems to be a resistor (maybe 470ohm?) as well.

@coderkind I’ve tested 2 custom-made cables. The first was a typical one with composite video wired as sync. Second one was made for a MD which had internal mod that extracted video level c-sync from CXA1145.

I can build a test firmware next week which has some additional settings that could help sync.

[afangus]

Hi, for me the MD1 in Av1 input is fixed : I’ve changed the two TTL values to 3, and baboom I’ve got a stable signal
So it’s working on AV1 with a perfect pictures, and on AV3 with some artefact on certains colours see my video on YouTube (av3 input) :

[coderkind]

@afangus; will hopefully return to try some tweaked settings later on today. The line triple mode looks awesome by the way; shame my TV doesn’t support it :'(

[coderkind]

@marqs; thanks. Going to try some of the tweaked settings suggested later hopefully too. In the absence of a cable or knowing which one I could buy off-the-shelf to definitely work with the OSSC I’m waiting to see if tweaking the settings will help (and after that, a firmware update).

By the way; what programming language is the OSSC Github repo in?

[afangus]

Hi
Some shmups over OSSC AV1 rgbs megadrive ^^

[marqs]

I built a small test circuit (500ohm resistor and 220uF cap in series) which should mimic that “clean sync” cable connected to DIN c-sync pin. I scoped the output of the that circuit vs a standard cable with composite video as sync – pictures here. While the c-sync output is cleaner (no chroma burst or video content), leading sync edges are less sharp and sync tips are narrower which are both bad for digitization. OSSC still synced fine with the MD1 I had for testing, so there may be some differences between models. I’d also like to know the resistor value used in that cable which can lead to different results. Anyway, I’d recommend normal composite as sync cable over a passive c-sync cable like that.

[coderkind]

I got my Genesis working with the OSSC; setting “analog sync LPF” to max sorted it, but the image is a bit flickery. Going to see if there’s any additional tweaks I can make to improve the picture.

[marqs]

Reducing “analog sync Vth” might mitigate jitter with such cable.

[Lukemcc]

I’e been having an email convo with Bucko and he asked me to post about my Megadrive setup in this thread. So i have a PAL Megadrive 1, Mega CD 1 and 32x Tower of Power! All 3 were modified with a switchless mod at the same time by videogameperfection (Ray). I tend to keep it all configured as NTSC US. I don’t recall where i bought the Megadrive to 32x stereo patch lead and 32x RGB scart cable. I normally buy all my cables from retro gaming cables but in this instance i didn’t and i can’t remember why, maybe he didn’t have any in stock. Any way if i change my Video LPF setting to 2.5mhz (High) i get a really good strong stable picture. So far I’ve only played 30 mins on Streets or Rage 2 and 20 – 30 mins on Mortal Kombat 2 (32x) but i don’t seem to get any artifacts or flicker at all. Not sure if this info is useful to anyone, or if anyone wants anymore info about my setup just let me know.

[Damianiw]

Hi

I have been using my OSSC with various consoles and recently acquired a ntsc genesis off eBay, I purchased an RGB cable as well but think it’s a poor cable and giving me problems with my ossc, using av1 it displays sync on the LCD display which looks correct but just black no picture – I did see the Briefist glimpse of a picture one time when sonic 2 did its interlaced demo section.

I connected the scart cable direct to my Sony LCD tv and get a picture but there is a lot of noise (hence my thoughts on the cable).

I opened up the scart socket and discover its mess with some capacitors hit glued not shrink wrapped, some resistors as well:

Basically I’m sure this is the problem but are there any tweaks I can do and what cable should I buy, preferably not a £50 one 🙂

I think I’m on latest firmware, will confirm version on here and provide a picture of cable inside.

[BuckoA51]

https://www.retrogamingcables.co.uk/sega/mega-drive-1/sega-mega-drive-1-sega-genesis-1-stereo-rgb-av-scart-cable-tv-lead

His standard cable works just fine for me, will be checking out his uprated one later too.

[eric90000]

I can also confirm that the RetroGamingCables.co.uk Sega Mega Drive 1 cable works fine with my Japanese MegaDrive. It’s the standard version, which has a 470ohm resistor and 220uF capacitor on the Csync line. It’s also got 75ohm resistors and caps on the RGB lines too. No sync LPF is needed to get a good image. Although on my TV (Samsung KS7000) I have to set “Allow TVP HPLL2x” to OFF, and “H-PLL Pre-Coast” AND “H-PLL Post-Coast” to 3.

On the topic of those “Packapunch” cables, I’m thinking of getting a few….do you guys think there’d be much of a difference in image/sound quality? I believe the only difference is he uses individually shielded conductors, rather than just one overall shield.

[Author]

Posts