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Japanese Mega Drive not outputting RGB/component

Posted: Tue May 28, 2019 11:42 am
by Nemoide
So earlier this year I got a Japanese (model 1) Mega Drive to expand my collecting into the world of Japanese games. It seems to work perfectly with composite video, but when I use my HD Retrovision component cables, it doesn't seem to work. When I hook it up, it sends a nice crisp image for a few seconds and then cuts out to nothing.

The HD Retrovision website mentions that sometimes it doesn't work properly because one of the pins in the AV port isn't sending the right signal and that reflowing the solder should fix it. I got a friend to help with the solder and... it's still not working.

Does anyone have any ideas as to what the problem might be and how it fixable it is? Or does anyone know of a repair service that would be willing to work with a Japanese retro console?
I can live with composite video if I have to but I'd really prefer to use my component cables.

Re: Japanese Mega Drive not outputting RGB/component

Posted: Tue May 28, 2019 9:18 pm
by Ziggy587
Are the HD Retrovision cables confirmed working? Can you use the RGB output of the Mega Drive in any way for testing?

Re: Japanese Mega Drive not outputting RGB/component

Posted: Tue May 28, 2019 10:18 pm
by pierrot
Is it an early revision of the Model 1 Mega Drive? I have a pretty early revision (not the earliest, but still non-TMSS), and it has always had an interesting quirk where it locks up after a time with Landstalker, Ragnacenty, and Legend of Heroes 1 and 2. It would not surprise me if early JP Mega Drives have some slightly different specs in places. The video output should be standardized, but it could be doing something to throw off the Retrovision cables.

What pin specifically did you reflow? What kind of solder was used? Specifically, was it lead-free? Is there any audio when the video drops out?

My guess is that there's potentially an issue with the sync signal, 5v line, or a grounding issue. All of these things can be tested, but you won't be able to tell much about the integrity of the sync signal without an oscilloscope. If you have a multimeter, it might be worth checking the voltage on the 5v pin (depends a little on what kind of devices the cable is using, but if it's out by more than +/- 5%, it could be an issue), as well as the resistance from the ground pin to the ground plane (should be very small).

Re: Japanese Mega Drive not outputting RGB/component

Posted: Wed May 29, 2019 8:54 am
by Nemoide
I've used the cables with my American model 2 Genesis, so they work. Although thinking about it, even though I've used the adapter for model 1/SMS with my SMS, I wonder if that might be the culprit; I'll test it with a multimeter. There is still audio output when the video cuts out, which makes me think it's MOSTLY working fine.
The unit is currently at a friend's house who has more soldering/electronics skills than I have; they did the work and while I'm not sure what solder they used I trust it was something appropriate.

I'll also try checking the AC adapter; I feel like this is a long shot, but maybe my American model 1 AC adapter will provide better results for some reason.

Re: Japanese Mega Drive not outputting RGB/component

Posted: Wed May 29, 2019 7:03 pm
by pierrot
Nemoide wrote:There is still audio output when the video cuts out, which makes me think it's MOSTLY working fine.

Yeah, so I would have said that potentially increases the probability that it's a sync issue, but it occurred to me that some of the component signals are going to be superpositions of the RGB signals, and the circuitry might actually lose video output with a problem on one of the RGB signals, if it's a mixed signal process. It's probably not going to be an issue with 5v or ground, but you could test it anyway, just to be sure. The RGB and sync outputs would really require an oscilloscope to verify any sort of serious signal distortion, or external coupling from other noisy sources.

Nemoide wrote:The unit is currently at a friend's house who has more soldering/electronics skills than I have; they did the work and while I'm not sure what solder they used I trust it was something appropriate.

Yeah, the only potential issue here is that mixing alloys can potentially alter the heat profile, and might reduce the integrity of any rework. It's probably not a concern in general, but lead solder mixed with unleaded solder would be a pretty dramatic mixture, and I know some people who just refuse to use lead solder.

Nemoide wrote:I'll also try checking the AC adapter; I feel like this is a long shot, but maybe my American model 1 AC adapter will provide better results for some reason.

US power supply would technically be better, but Japanese power is nominally ~17% out of US specifications, and most of the critical components in the Mega Drive are given a regulated voltage, internally. That said, the unregulated DC off the power supply is used for the rails on a lot of the analog audio and video circuitry. The only real concern is that the rails might be reduced enough by the difference in transformer winding ratio that the signals would start to clip, but I doubt it because those signals probably aren't greater than 3.25 V in peak magnitude. You may as well use the US adapter, anyway, though. There's at least a possibility that it would solve the issue.