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Sega Genesis AC Adapter Compatibility


Stevie Goodwin
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Hi all. I'm in the process of testing power adapters for a Model 1 Genesis
and what I got was a strange flickering screen with buzzing noise.
Pictures of the screen are here:

Why does a Genesis do this?
The VA2 to VA6 will do this but would Japanese Mega Drive VA0 or VA1 do this?

Edited by Stevie Goodwin
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I already explained this to you in a PM...

 

You used a NES power supply in the Genesis. And the NES power adapter is an AC to AC adapter...not an AC to DC adapters like most of the rest of the console world used back then. As I also told you, you are lucky you didn't fry the Genesis in the process of doing this because the current from the AC could easily have smoked it.

 

You shouldn't just try any adapter in a Genesis... you need to make sure the adapter puts out at least 9v with a 1amp current and center tip negative on the model 1 Genesis. Anything not meeting those specs is trouble and I'm not sure why you would risk it?

Edited by -^Cro§Bow^-
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You are missing the point, I believe Stevie is doing this out of curiosity vs need. He sent me links for two videos he did showing the use of other power supplies. In them he also has a legit power supply and simply wants to know why the others do not function proper. I tried to explain to him in a reply to a PM he sent me explaining this.

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I already explained this to you in a PM...

 

You used a NES power supply in the Genesis. And the NES power adapter is an AC to AC adapter...not an AC to DC adapters like most of the rest of the console world used back then. As I also told you, you are lucky you didn't fry the Genesis in the process of doing this because the current from the AC could easily have smoked it.

 

You shouldn't just try any adapter in a Genesis... you need to make sure the adapter puts out at least 9v with a 1amp current and center tip negative on the model 1 Genesis. Anything not meeting those specs is trouble and I'm not sure why you would risk it?

I can verify an NES PS definitely will fry a Sega Genesis. I fried my brothers Genesis back in the early 90s by doing just that. Luckily we were able to exchange it for another unit.

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  • 5 weeks later...

Alright, I found a Power Adapter that is compatible with Genesis.

But i changed the polartiy on it so the Genesis would power up and it works and no buzzing noise or the screen from the video: https://www.youtube.com/watch?v=ZDLx8ggRz4Q&t=12s

 

The new adapter specs are:

Input 120VAC 60Hz 32W

Output 12VDC 1200ma

 

and the original 1602 is

Input 120V 60Hz 17W

Output 9V DC 1.2A.

 

Is this new adapter a safe substitute to use on my Model 1?

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Personally I think the 12 volt adapter is fine. The Genesis comes standard with 7805c regulators. From the spec sheets I've seen, that means they put out 5 volts at up to 1.5 amps. And they have a minimum required voltage of 7v and can take a max of 25v input. Now, the more volts you put into the regulator the more has to be shed off as heat for the drop back to +5. But the heatsink assembly in the genesis is fairly large and if you still attach the EMF shield it acts as a secondary or sorts when screwed down flush against the top portion of the heatsink. To make sure of this, you need to measure what the actual input voltage is going into the regulators with the 12v supply attached. My guess is that it would be somewhere around 16v and an empty load reading of about 17 - 18v. Just guesstimates.

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Personally I think the 12 volt adapter is fine. The Genesis comes standard with 7805c regulators. From the spec sheets I've seen, that means they put out 5 volts at up to 1.5 amps. And they have a minimum required voltage of 7v and can take a max of 25v input. Now, the more volts you put into the regulator the more has to be shed off as heat for the drop back to +5. But the heatsink assembly in the genesis is fairly large and if you still attach the EMF shield it acts as a secondary or sorts when screwed down flush against the top portion of the heatsink. To make sure of this, you need to measure what the actual input voltage is going into the regulators with the 12v supply attached. My guess is that it would be somewhere around 16v and an empty load reading of about 17 - 18v. Just guesstimates.

Volts go through several other components before even reaching the 7805.

Edited by chilicheesefried
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Volts go through several other components before even reaching the 7805.

 

Such as? Cause when I was tracing the power adapter plug wires back to the main PCB on my Model 1, they pretty much just traced straight to the 7805s and then everything else fed off from there... I'm sure there is a cap or two in there for filtering, but they are likely rated at much higher than 12v. Schems on the va3 and va2 essentially, show the same. Each 7805 controlling different aspects of the system. As seen below..

 

https://console5.com/techwiki/images/6/63/Mega_Drive_1_-_VA3_-_CPUs%2C_RAM_%28Sheet_1%29.png

 

VCC1 essentially provides power to the 68k, Expansion ports both back and side, cartridge connector, & video ram.

VCC2 seems to power the system ram and other subsystems like Bios, but primarily provides the power to the audio circuits and video out subsystems like the encoder and RF modulator.

 

Interesting... I think I need to give the DC/DC conversion another try but only change out VCC1 and leave the 7805 in place for VCC2.

Edited by -^Cro§Bow^-
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Let me see if I can find the diagram.

 

Started a thread looking for my schematic.

 

I believe this to be a correct schematic of an early version.

 

All of these components are aging.

 

Power_Section_Several.png

 

Yeap good points there. The diodes I'm not sure what their ratings are nor the caps located at c2, c89, c3,c73,c83, and c84 as they aren't part of a standard cap replacement process it appears. But the other caps in line at c1 and c79 appear to be 16v and sure enough c4 and c74 are only 10v. But that seems crazy because even my standard genny 1 wall wart puts out 14v without a load and well over 12v under load to the inputs on the 7805. so it would seem the caps are already being over voltage along the way before the 7805s get involved. Might be why the replacements are usualy 25v and 16v in most places of the 10v originals?

 

But yes there are several passive components there in the mix before the 7805s. Still given the ratings of those components and what the standard PS are putting out...seems they handle it all quite well?

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I already explained this to you in a PM...

 

You used a NES power supply in the Genesis. And the NES power adapter is an AC to AC adapter...not an AC to DC adapters like most of the rest of the console world used back then. As I also told you, you are lucky you didn't fry the Genesis in the process of doing this because the current from the AC could easily have smoked it.

 

You shouldn't just try any adapter in a Genesis... you need to make sure the adapter puts out at least 9v with a 1amp current and center tip negative on the model 1 Genesis. Anything not meeting those specs is trouble and I'm not sure why you would risk it?

I stopped doing that now and what does smoked mean?

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Okay i'm sorry i didn't mean to make you lose your patience but what Atari system can a screen happen like this. I'm still using a Sega 1602 adapter as i should and it doesn't make this screen. The Genesis i used was a Model 1 VA2.

 

https://www.youtube.com/watch?v=ZDLx8ggRz4Q&t=12s

 

So this is what happens if you use a wrong power adapter? I get it now.

 

What is this screen in the video called.

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  • 2 weeks later...

That is because the 850ma isn't strong enough to give a good signal through the system. Again, the model 1 requires a 1amp current. Now, oddly enough, the model 2 power supply I've seen rated at only about 850ma. It is hard to keep track because it seems all the various add-ons for Genesis each had their own power supply and each of those usually had slightly different specs. Gets worse when you start talking about the x'eye and CDX systems.

 

It is because of this that when I'm looking for a replacement power adapter for my Sega systems, I always make sure to get at least these specs:

 

10v output

1.2 - 1.5 amp

 

Polarity:

Center tip - (Model 1 HDG Genesis and Model 1 SegaCD)

Center tip + (Model 2/3 Genesis systems and 32x)

 

The polarity will change depending on if you are getting a power adapter for the model 1 or model 2 systems. But pretty much as long as you stick to those specs in regards to the output voltage and amperage...you have the Sega line covered from SMS to a Genesis with all attachments.

Edited by -^Cro§Bow^-
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