When I switch on my Saturn, my Model 1 Genesis draws Power through the SCART cable???

[Phantar]

Okay, I have a really curious issue here!

My Saturn had a busted PMC. I've managed to replace it and it works fine now, but I've noticed another, rather curious problem.

(I live in a PAL region country btw, so most of my consoles use SCART cables for the TV and audio signal)

Due to space restraints, both my Model 1 Genesis and my Saturn are hooked up to my CRT by way of a simple, 5-port passive SCART splitter box. When I tried switching the Saturn on the other day, I got a distorted picture, as if there was some sort of signal interference going on. When I checked, I noticed that the power indicator of my Model 1 Genesis (PAL Mega Drive) was burning - even though the console itself was switched off. The problem remained even after I disconnected the power supply from the Genesis. The problem was only resolved when I unplugged the video connection to the Genesis. If I leave the Saturn off and only turn on the Genesis, there are no issues. And none of the other platforms hooked up to the same SCART splitter (a SNES, an XBOX classic and a Commodore Amiga) seem to be affected when I turn on the Saturn, just the PAL Model 1 Mega Drive.

For the moment I just leave the Genesis video cable disconnected whenever I want to use the Saturn, but this issue is puzzling the heck out of me - why is the Genesis (allegedly) drawing power, and where is it drawing the power from? How can the Saturn and the Genesis interfere with one another through a SCART cable/splitter box when one of the consoles is turned off? (I guess I could try hooking up the Genesis to the RGB-in of my CRT TV instead, but I would need an SCART-to-RGB-adabter to try that first, since I only have RF- and SCART-Connectors for the console. And no, I don't want to use the RF-cable for my Genesis when I have a better video option available - besides, the antenna in is already in use by two other computer platforms hooked up to the TV).

[CrossBow]

The same thing will happen if you use one the more modern Genesis to 32x video patch cables. In that instance just having the 32x plugged in causes the Genesis to be powered on and the on/off switch has no effect. This is because the 32x AV in apparently has the +5 active on it and it backfeeds into the Genesis AV port (which also has a +5 on it). These ports were originally designed to be used to provide +5 out of the AV ports but they will work in reverse as well.

My guess here is that your passive SCART switcher has the +5 line tied across to all the inputs. When you switch on the Saturn it is providing +5 out of the AV out into the SCART switcher, that in turn is backfeeding the +5 into the Genesis through the SCART switcher and back into the AV out port of your Genesis.

In the case of the 32x causing this, the simple fix is to remove the pin on the cable that plugs into the 32x that provides the +5. I'm sure something similar could be done here although it is worth noting that the +5 is needed with some AV devices to provide them with power. I have an auto SCART switcher and it uses that +5 to know the signal is active from that device and switch over to it. The +5 is also needed by some of the modern cable adapters like the RAD2x etc.

So again, the Saturn AV out is providing +5 output and that is backfeeding into the Genesis and causing it to remain powered on. I've not looked into this but I would imagine that a simple diode installed in-line of the +5 outputs from the AV out port of the Genesis would be enough to ensure that the +5 will only go out of the AV port and not backfeed into the Genesis. Would require cutting the +5 trace just before the AV out port and then install the diode to bridge that trace but only allowing the +5 to flow out of the Genesis and not back into it.

[gamevet]

A diode will stop that problem.

*Editt* I didn't see that you had suggested a Diode too, Crossbow.

[Phantar]

Thanks for the thorough explanation. 😁

[GohanX]

I had a Bandridge 5 port scart switch a while back that did this from one of the ports. I don't remember the specifics, but that one port was supposed to be dedicated to a VCR and needed to be wired differently for some reason. I discovered it when I turned on my SNES and heard the Dreamcast fan come to life. I never bothered to mod the switch, I just used it as a 4 port from then on.

[Phantar]

Hm, interesting. Changing the plugs to different ports doesn't resolve the problem on my end though, so it could be that all the Scart ports on my splitter are wired the same way. So I will either go the diode route, or circumvent the issue altogether by getting an Rgb cable or adapter and plug one of the consoles into the TV's Rgb in directly, circumventing the splitter issue (of course, I have plenty of Rgb to Scart adapters but can't seem to find one going the other way lying around, so I would need to buy one. They're not really expensive though, do maybe I'll just do that if I feel lazy about it ).

[cleeg]

I had a Bandridge 5 port scart switch a while back that did this from one of the ports. I don't remember the specifics, but that one port was supposed to be dedicated to a VCR and needed to be wired differently for some reason. I discovered it when I turned on my SNES and heard the Dreamcast fan come to life. I never bothered to mod the switch, I just used it as a 4 port from then on.

This for me too. I found a vid that told me to cut a trace which completely solved the issue.

EDIT - I have PM'd you Phantar.