Image shift w/ HD Retrovision cables on Genesis Model 2

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SitarH
Posts: 2
Joined: Sat Mar 25, 2023 1:51 am

Image shift w/ HD Retrovision cables on Genesis Model 2

Post by SitarH »

I’ve asked this elsewhere, but figured I’d try here too:

I got the HD Retrovision YPbPr cables for my stock Model 2, VA1/1.8 genesis. The image quality is much improved over RF, but the image itself is now off-center and cut off on the left side. The image over RF input does not have this problem. I've tested this on two TVs - one CRT, one LCD (both capable of YPbPr and RF input) - and I have the same issue on both.

Image over Component

Image over RF

Has anyone else had this issue? I’m the only owner of this Genesis so I know it hasn’t been modified. Based on what I’ve read online, it might be due to the sync-on-composite the HD Retrovision uses - the CVBS has a time delay compared to the RGB signals used to generate the YPbPr signal.

could this be fixed by rewiring/soldering the mini-DIN on thegenesis to put CSYNC on the pin that normally hosts composite signal? If so, will I have to put a resistor/cap on the CSYNC pin - or can the Retrovision cable handle TTL sync? Additionally, could this be a capacitor issue? The console has never been recapped, but I don’t see any leaks on the motherboard and everything plays fine. I suppose it’s also possible I have a busted cable and need to exchange it?

Thanks for the help.
KPackratt2k
Posts: 211
Joined: Sun Apr 04, 2021 11:02 pm
Location: Seattle, WA, USA

Re: Image shift w/ HD Retrovision cables on Genesis Model 2

Post by KPackratt2k »

SitarH wrote:could this be fixed by rewiring/soldering the mini-DIN on thegenesis to put CSYNC on the pin that normally hosts composite signal? If so, will I have to put a resistor/cap on the CSYNC pin - or can the Retrovision cable handle TTL sync?
If you install a Triple Bypass Mod on your Genesis to bypass the video encoder, it can route attenuated (75 ohm level) CSYNC to the Composite video pin of the Multi-out.

I doubt capacitors could be the culprit of the issue. The time delay between Composite and RGB is a common problem with any video game console that outputs both signals, and is usually corrected by using CSYNC instead of Composite video for sync. Unfortunately, due to the HD Retrovision cables internally using Composite video for sync, your options are to either do the Triple Bypass Mod (and lose Composite video output in the process) or figure out how to rewire the HD Retrovision cable to use CSYNC instead, which is easier said than done because you would have to disassemble the Mini-DIN connector on the cable to reroute the pin and (more than likely) somehow manage to fit a 470 ohm resistor and a 220uF capacitor inside, both of which are extremely difficult to manage.

If Composite video and RF output aren't important to you, I'd suggest Triple Bypass modding your Genesis. Considering the revision you have, it would greatly improve the AV output quality of your console, mainly on the audio side of things due to the lossy amplification that the audio goes through on the stock circuit on early Model 2 consoles.
SitarH
Posts: 2
Joined: Sat Mar 25, 2023 1:51 am

Re: Image shift w/ HD Retrovision cables on Genesis Model 2

Post by SitarH »

I actually went ahead and wired the CVBS av out pin directly to the CSYNC output from the VDP (tested by attaching a 68 ohm resistor as load to ensure to ensure voltage wasn’t too high). This reduced the shift by maybe 25% or so. It’s still fairly significant.

I think this means I either have a busted VDP or busted cables. I’m going to test the cables on another model 2, and if that also has shift - I’ll just return/exchange the cables.

I also just received the 3BP board. I plan to install it once I get to the bottom of this issue!”.

Thanks for the help!
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